US20090112336A1 - System and method for implementing time synchronization monitoring and detection in a safety instrumented system - Google Patents

Abstract

An apparatus, system and process is provided from communicating safety-related data, over an open system, from a sender to a receiver. Safety-related components, including function blocks, flexible function blocks, resource blocks and transducer blocks, as well as, safety-related objects are provided. Also, a time synchronization monitor is provided for monitoring timing distributions and determining when such distributions have drifted beyond an acceptable limit.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a continuation of U.S. patent application Ser. No. 11/642,498, filed Dec. 19, 2006, which claims the benefit of U.S. Provisional Application No. 60/752,272, filed Dec. 20, 2005, and U.S. Provisional Application No. 60/752,476, filed Dec. 20, 2005, which are incorporated herein by reference.
• This application incorporates by reference, in their entirety, the disclosures in the following U.S. patent and patent applications: (a) U.S. patent application Ser. No. 10/826,576, filed on Apr. 16, 2004 and entitled “System and Method for Implementing Safety Instrumented Systems in a Fieldbus Architecture”; (b) U.S. provisional patent application No. 60/463,334, filed on Apr. 17, 2003 and entitled “Safety Instrumented Systems Function Blocks”; (c) U.S. patent application Ser. No. 10/453,596, filed Jun. 4, 2003 and entitled “Flexible Function Blocks”; (d) U.S. patent application Ser. No. 10/160,094, filed Jun. 4, 2002 and entitled “Block-oriented Control System”, now U.S. Pat. No. 6,594,530; and (e) U.S. patent application Ser. No. 08/916,178, filed Aug. 21, 1997 and entitled “Block-oriented Control System”, now U.S. Pat. No. 6,424,872.
• The present application also incorporates by reference the disclosures set forth, in their entirety, in the following patents and/or patent applications:
• • U.S. Provisional Patent No. 60/024,346, entitled “A Block-Oriented Control System,” filed Aug. 21, 1997;
  • U.S. patent application Ser. No. 09/598,697, entitled “Block-Oriented Control System On High Speed Ethernet,” filed Jun. 21, 2000;
  • U.S. Provisional Patent Application No. 60/139,814, entitled “Foundation Fieldbus on HSE,” filed on Jun. 21, 1999;
  • U.S. Provisional Application No. 60/384,846, entitled “Flexible Function Blocks,” filed Jun. 4, 2002; and
  • U.S. patent application Ser. No. 10/226,282, entitled “Integrated Fieldbus Data Server Architecture,” filed Aug. 23, 2002.
TECHNICAL FIELD
• The technical field, to which the various embodiments relate is control system architecture. More particularly, the technical field relates to systems and methods for controlling the functions and operation of safety instrumented systems in automatic control systems. Even more particularly, certain embodiments relate to systems and methods for controlling safety instrumented systems in the context of an automatic control system which links device controllers via a control network to facilitate control of industrial, manufacturing and other processes.
BACKGROUND
• Industrial, manufacturing, petrochemical and other “automation industries” implementing complex processes and systems have been migrating from proprietary, centralized architectures to open, decentralized architectures to facilitate automation of such processes and systems. Decentralized architectures commonly implement fieldbus control systems and networks wherein control is distributed amongst the various devices within the network and/or system. Examples of open, interoperable and decentralized fieldbus architectures include the FOUNDATION™ fieldbus from the Fieldbus Foundation (Austin, Tex.), PROFIBUS from PROFIBUS International (Karlsruhe, Germany); LonWorks from Echelon Corporation (San Jose, Calif.), industrial Ethernet, high speed Ethernet and other types of network architectures. Such networks, regardless of actual configuration, data transmission speeds supported thereby or the like are hereafter, collectively referred to as “fieldbus Architectures”.
• The demand for open and interoperable, distributed control fieldbus systems is often driven by equipment suppliers and users. Suppliers commonly prefer fieldbus Architectures because it allows them to sell their products and/or services to more users, instead of only to users operating a specific proprietary system. Users desire to utilize fieldbus Architectures, for example, because it often enables them to select the fieldbus devices and/or services from multiple suppliers instead of only devices specifically designed for a proprietary system.
• Many sectors of the automation industry also have a need for special “safety” systems to ensure the safety of plant personnel and to prevent damage to equipment due to unexpected events. These special “safety” systems are collectively called “Safety Instrumented Systems” (SIS). Users and suppliers often require SIS systems to comply with international safety standards such as International Ebctotechnical Committee (IEC) 61508 (functional safety of electrical/electronic/programmable electronic safety-related systems), and IEC 61511 (functional safety: safety instrumented systems for the process industry sector). Currently available SIS control solutions are commonly proprietary and are not compatible with fieldbus Architectures.
• Thus, users and suppliers of SIS devices and systems have a need for an open, interoperable SIS fieldbus Architecture (hereafter, an “SIS fieldbus”) that enable users to support and/or provide SIS control using existing fieldbus Architectures. Desirably, a SIS fieldbus is directly compatible with existing fieldbus Architectures and do not require modification to existing communication protocols, function blocks and/or other network aspects.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
• FIG. 1 is an overview of an extended control system which may be utilized in conjunction with one or more embodiments to support a SIS fieldbus.
• FIG. 2 shows the Open Systems Interconnect layered communication model as compared to the communication model described herein.
• FIG. 3 illustrates a hardware embodiment of a field device.
• FIG. 4 summarizes the virtual communication relationships provided by the Fieldbus Access Sublayer.
• FIG. 5 illustrates two devices interconnected via the communication services one with safety-related components and one without safety-related components.
• FIG. 6 illustrates an object dictionary.
• FIGS. 7A and 7B illustrate the virtual communication devices within the communication model for use in safety and non-safety devices.
• FIGS. 8A and 8B illustrate a function block application structure within a field device containing safety and non-safety related components.
• FIGS. 9A and 9B illustrate external devices interconnected on a bus with field devices for safety and non-safety implementations.
• FIG. 10 illustrates the layout of an object dictionary directory object.
• FIG. 11 illustrates examples of parameters interconnected for a single loop for safety and non-safety related components.
• FIG. 12 illustrates one embodiment of a system architecture.
• FIG. 13 illustrates a safety-related function block with user configurable inputs, user configurable outputs, and a user configurable algorithm.
• FIG. 14 illustrates an application using standardized safety and non-safety related function blocks and flexible function blocks.
• FIG. 15 is a block diagram illustrating an example of an application using standardized, flexible function blocks and FFBS.
• FIGS. 16A,16B and16C are a flow diagram illustrating one methodology by which data may be communicated, using a publisher-subscriber topology, and authenticated for safety-related function blocks and safety-related flexible function blocks.
• FIGS. 16D,16E and16F are a flow diagram illustrating another methodology by which data may be communicated, using a publisher-subscriber topology, and authenticated for safety-related function blocks and safety-related flexible function blocks.
• FIGS. 17A,17B and17C are a flow diagram illustrating one methodology by which data may be communicated, using a client-server topology, and authenticated for safety-related function blocks and safety-related flexible function blocks.
• FIGS. 17D,17E and17F are a flow diagram illustrating another methodology by which data may be communicated, using a client-server topology, and authenticated for safety-related function blocks and safety-related flexible function blocks.
DETAILED DESCRIPTION
• As described herein, various exemplary systems, components and methods (hereafter, collectively “systems”) are described for utilizing SIS devices in fieldbus Architectures. The various systems set forth herein may be utilized in various types and forms of SIS devices as well as in various types of fieldbus Architectures. Further, the various systems may desirably be utilized in various fieldbus Architectures without significant, and preferably no, changes to the protocols, methodologies or other processes currently utilized in fieldbus Architectures to communicate non-SIS information across the network for notification to and/or utilization by network compatible fieldbus devices.
• More particularly, a SIS implementation may include an apparatus configured for operating in an open control system that includes: a memory, which includes system management data; one or more SIS elements; a processor, operably connected to the memory; a medium attachment unit, which translates input messages and output messages between the processor and a transmission medium; and an extended safety or safety-related protocol (“SISRP”), which provides the desired level of security needed for a particular SIS implementation. The system management data may include system schedule information which the processor desirably executes as specified by the system schedule.
• A SIS implementation in a fieldbus Architecture can permit, for example, interoperability between a plurality of devices, at least one of which includes a SIS component (“SISC”), such as a resource block, a function block, a transducer block or a link object, and a medium attachment unit, operably connected to the SISC. In such an embodiment, the resource blocks uniquely identify each device, the function block processes parameters to produce an output message, and the medium attachment unit translates input message(s) received, for example, from a transmission medium to the SIS device and output messages from the SIS device to the transmission medium. Such an embodiment may be considered to be a function block implementation.
• An apparatus can be used which desirably includes: a user layer, that includes an encapsulated SISC to provide functionality; a physical layer, which translates messages from a transmission medium into a suitable format for use by the user layer and from the user layer into a signal for transmission on the transmission medium; and a communications stack, connected to the user layer and the physical layer. The communication stack may include a data link layer and an application layer. The data link layer controls the transmission of messages onto the transmission medium. The application layer allows the user layer to communicate over the transmission medium.
• Similarly, a SIS implementation in a fieldbus Architecture can permit interoperability between a plurality of devices, wherein at least one device includes a resource block, a link object, and a medium attachment unit, operably connected to the link object. The resource blocks can be adapted to uniquely identify each device, the link object can be adapted to receive processed parameters and produce an output message, and the medium attachment unit can translate an input message from a transmission medium to the link object and the output message from the link object to the transmission medium.
• An apparatus can be utilized that includes: a user layer, which includes one or more encapsulated SISC(s) to provide functionality; a physical layer, which translates messages from a transmission medium into a suitable format for the user layer and from the user layer into a signal for transmission on the transmission medium; and a communications stack, connected to the user layer and the physical layer. The communication stack includes a data link layer and an application layer. The data link layer controls the transmission of messages onto the transmission medium. The application layer allows the user layer to communicate over the transmission medium.
• Likewise, a memory can be used to store data for access by an application framework operating in a device within a control system. The memory includes a data structure stored in the memory, the data structure including one or more SISCs, such as a resource block, which makes hardware specific characteristics of the device electronically readable, an encapsulated function block, and/or at least one transducer block. The function block includes end-user configured program and parameters and the at least one transducer block controls access to the function block.
• Thus, it is to be appreciated that various devices and systems can be used and that such devices and systems can utilize SISCs and/or a SISRP to incorporate SIS devices into fieldbus Architectures. For purpose of clarity and simplicity, however, the following description relates primarily to one embodiment of a fieldbus Architecture, namely, one which utilizes function blocks to provide a general structure for specifying different types of device functions while utilizing a common fieldbus communications network. Other architectures and embodiments, however, may be used in conjunction with the systems described herein.
• As is commonly known and appreciated, a function block implementation of a fieldbus Architecture defines the internal components of an application, or portion thereof, implemented by a device to provide for system operation. Function block applications specify how each application, or portion thereof, interfaces with each other application in the system so as to provide for standardized inter-operability between devices.
• One implementation of a function block implementation of a fieldbus Architecture has been specified as the FOUNDATION™ fieldbus specifications as provided by the Fieldbus Foundation of Austin, Tex. As is commonly known and appreciated, the FOUNDATION™ fieldbus specifies a lower speed fieldbus (H1) optimized for process control, and a High Speed Ethernet (HSE) fieldbus backbone for high performance control, subsystem integration, and management information systems integration. The control system can support a variety of field devices, including sensors and actuators, or high speed field devices, such as cell control, motors, drives and remote input/output (I/O). Since FOUNDATION™ fieldbus is open and interoperable, distributed control architecture, control devices from by different vendors interoperate on the H1 or HSE fieldbus and share the control functions (e.g., control is distributed into the fieldbus devices). Distribution of control into the fieldbus devices often reduces system installation cost because the need for centralized control computers and I/O subsystems are reduced or eliminated. Further, distribution of control into fieldbus devices often reduces system operating and maintenance costs because standard function blocks in the devices provide more information about process measurements and device status. It is in this context, that one embodiment for providing for fieldbus control of SIS devices is set forth herein. It is to be appreciated, however, that other implementations may be used, including those compatible with and/or incorporated into other fieldbus Architectures.
• In particular, a FOUNDATION™ fieldbus Architecture is provided with a control system architecture with extended and additional communication security. Such communication security is provided in addition to and/or “above” the security provided by existing communication systems while utilizing new, security related, function blocks which are compatible with an existing function block framework, such as the framework provided in the FOUNDATION™ fieldbus specifications. It is to be appreciated that the new system commonly eliminates and/or significantly reduces, the need for expensive and difficult to maintain custom control software and special input/output “I/O” devices for SIS applications. The safety-related function blocks described herein, with reference to this and similar embodiments, are collectively referred to herein as Safety Instrumented System Functions Blocks (“SISFB”)—one embodiment of a SISC.
SISFB System Overview
• As shown inFIG. 1, a field device (which may contain one or more SISCs) is one which operates on a fieldbus Architecture control system and is generally categorized as a non-SIS compatible linkactive scheduler100, a SIS compatible linkactive scheduler100′, a (non)-SIScompatible link master105/105′, or a (non)-SIS compatiblebasic device110/110′. As is discussed in greater detail below, SIS and non-SIS components in SIS devices (i.e., link active schedulers, link masters and basic devices) are substantially similar, but, SIS components utilize an additional extended safety or SISRP to ensure communications between SISCs are secure and have not been corrupted, modified or otherwise degraded. Thus, when SIS devices are included in a fieldbus Architecture control system, such SIS field devices may be further categorized as a SIS linkactive scheduler100′, aSIS link master105′, or a SISbasic device110′. SISCs may communicate with other SISCs and/or non-SISCs (for example, for purposes of reporting and other uses) using existing fieldbus Architectures such asbus120 and/or120′.
• Regardless of whether a field device includes a SISC, a field device is categorized based upon its control capabilities and responsibilities. For example, a field device is categorized as a linkactive scheduler100/100′ if it is acting as network controller of abus120/120′. A field device is categorized as alink master105/105′ if it is capable of acting as the network controller or link active scheduler, but has not assumed that responsibility. Abasic device110/110′ is not capable of acting as the network controller.
• The field devices are electronically coupled or connected by atransmission medium120/120′, which can be individual input and output wires or a variety of bus configurations. As shown inFIG. 1, a bus configuration can be used by which both field devices with SISCs and non-SISCs may be connected. The throughput rate of the bus may vary. A few of exemplary buses are the 31.25 kbit/s H1 bus and the 100 Mbit/s HSE bus. However, other bus data transfer rates and configurations may be suitably utilized. Such embodiments may utilize other high speed or low speed network configurations and may or may not use function blocks.
• Bus data transfer rates are generally independent of whether SISC and/or non-SISC field devices are connected to the control system. The bridges130 (FIG. 1) andbuses120/120′ may be suitably replaced by other system configurations. For example, one embodiment may utilize HSE devices which are connected in a star topology by Ethernet switches. Other system and/or network embodiments may also be utilized.
• In one embodiment, however, the H1 bus is generally used for process control applications, such as temperature, level, and flow control. The HSE bus is generally used for high speed applications. Devices operating on HSE buses are usually self-powered or draw power from a separate power bus in the fieldbus cable (i.e.,4 wire cable), however, they can also be powered directly from the fieldbus.
• As shown inFIG. 1, severallink master devices105/105′ can operate on the bus(es)120/120′. When theselink master devices105/105′ are activated, these (SIS) linkmaster devices105/105′ bid for the responsibility of becoming the linkactive scheduler100/100′. Thelink master device105/105′ which becomes the linkactive scheduler100/105′ is the device with the lowest network address. Alternatively, a particular device may be the “preferred” link master. In which case, when the system is activated thelink master105/105′ with the lowest network address would assume the responsibilities of the linkactive scheduler100/100′. Then, the “preferred”link master105/105′ would send a message to the linkactive scheduler100/100′ directing it to transfer control. Upon receipt of the message, the linkactive scheduler100/100′ would transfer control to thepreferred link master105/105′.
• Further, when SIS devices are connected to the control system, for example, onbus120 or120′, the link master designated as the link active scheduler is desirably SIS compatible. As shown inFIG. 1, thebus120′ is suitably controlled by a SIS linkactive scheduler100′ because of the existence of the SISbasic device110′ on thenetwork120′. As is discussed in greater detail hereinbelow, SISCs inSIS field devices110′ are commonly configured to accept inputs and instructions from SISCs in other SIS devices and not from non-SISCs in SIS or non-SIS devices. Non-SISCs in SIS or non-SIS devices, however, commonly can accept inputs and instructions from SISC or non-SISC components. Thus, when SISCs are included in a network, desirably the designated link master scheduler includes any necessary SISCs.
• Whenmultiple link masters105/105′ exist on abus120/120′, there are a variety of ways to conduct the bidding process. For example, one type of bidding process is shown in U.S. Pat. No. 5,526,358, issued Jun. 11, 1996, which is hereby incorporated by reference in its entirety. The bidding process may also be conducted if the linkactive scheduler100/100′ controlling abus120/120′ malfunctions or is removed. Yet, whenSIS devices105′ are on a bus, the link active scheduler should be selected from an availableSIS link master105′.
• The control system can also include abridge130 to interconnect individual buses and create larger networks. Communication between the individual buses can be monitored by one ormore operator stations150. Further, in a SIS embodiment, the operator stations are desirably SIS compatible.
• Further, alink master105/105′ desirably contains the same control capabilities as a linkactive scheduler100/100′. Thus, the capabilities of both are discussed further herein with reference to a link master. More particularly, alink master105/105′ incorporates a program interface comprising the following three layers: (1) a physical layer, (2) a communications stack, and (3) a user layer. When SISCs are utilized in field devices, the user layer further includes and utilizes a SISRP or interface, as is discussed in greater detail hereinbelow. Otherwise, SIS and non-SIS compatible components utilize common physical layers, communications stacks and user layers.
• Referring now toFIG. 2, the physical layer (PHY)200 and the communications stack205 are derived from the Open Systems Interconnect (OSI) model. The physical layer (PHY)200 is desirably the same asOSI layer1, and the communications stack205 generally corresponds toOSI layers2 and7. Theuser layer235 is not defined by the OSI model. Alternatively, thephysical layer200 and communications stack205 may be derived from a variety of different networking standards, such as Transmission Control Protocol/Internet Protocol (TCP/IP), UNIX and others. A detailed description of each of these layers follows. Desirably, for both non-SIS and SIS implementations, thePHY200 and the communications stack are the same. The commonality in these layers enables SIS devices to be connected to existing fieldbus Architectures without requiring changes to communications protocols currently utilized by non-SIS devices. As such thephysical layer200 and communications stack205 are described herein with regards to a common or generic (i.e., non-SIS) fieldbus Architecture.
Physical Layer
• As shown inFIGS. 1 and 2, thephysical layer200 receives messages from thecommunication stack205 and converts the messages into physical signals on thetransmission medium120/120′ and vice versa. Thephysical layer200 may be defined by approved standards from the International Electrotechnical Commission (IEC) and the International Society of Measurement and Control (ISA). For more information about thephysical layer200, see ISA document S50.02-1992 and IEC document 1158-2, both of which are hereby incorporated by reference in their entirety. It is to be appreciated, however, that the physical layer may also be defined by other standards commonly known in the art.
• Messages can be encoded using, for example, the well known Manchester Biphase-L technique and the clock signal can be embedded in the serial data stream. Again, other encoding schemes may be utilized, as desired and/or specified by the implementation and networking standards being utilized in any particular embodiment. The hardware required to translate inbound messages from thebus120/120′ and outbound messages from a processor within the device is generally called the medium attachment unit, such as a network adapter. After thephysical layer200 translates an inbound message from thebus120/120′, it forwards it to thecommunications stack205. Thecommunication stack205 is described below.
Communications Stack
• FIG. 2 shows acommunications stack205 which includes thedata link layer210, thefieldbus access sublayer220 and thefieldbus message specification230. These layers (205,210,220 and230) are desirably common to both SISCs and non-SISCs. Also, for at least one embodiment, the data link layer is the same asOSI layer2, while thefieldbus access sublayer220 andfieldbus message specification230 are sublayers within the OSI application layer, OSI layer7. The communications stack205 does not use layers3-6. The layers of the communications stack205 are described below.
Data Link Layer
• Thedata link layer210 controls transmission of messages onto thebus120/120′ from a linkactive scheduler100/100′,link master device105/105′ orbasic device110/110′ based on the instructions received from a network controller or the linkactive scheduler100/100′. Thedata link layer210 can be a subset of the IEC and ISA data link layer standards.
• The linkactive scheduler100/100′ controls thedata link layer210 according to a network schedule stored in a memory. The network schedule is a list of transmit times for data buffers within the system. The data buffers store data collected by the field devices. For example, if the field device is a thermometer, the data buffer stores the temperature, and upon command, publishes the temperature reading onto thebus120/120′. Additionally, the linkactive scheduler100/100′ maintains a “live list” by periodically transmitting a pass token message. Using the “live list,” the link active scheduler can identify all the field devices operating on the system. Any field device properly responding to the pass token is kept on the live list. If a field device fails to respond to the pass token after a predetermined number of attempts, the device is removed from the live list. Since multiple networks may be connected by bridges and otherwise, in one embodiment, each linkactive schedule100/100′ desirably keeps a “live list” for those components on each respective network.
• New devices can also be added to the live list. The linkactive scheduler100/100′ periodically sends probe node messages to network addresses not listed in the live list. If a field device is present at the network address and receives a probe node message, the field device immediately returns a probe response message. If the field device answers with a probe response message, the linkactive scheduler100/100′ adds the field device to the live list and confirms the field device's addition by sending the field device a node activation message.
• Whenever a field device is added or removed from the live list, the linkactive scheduler100/100′ broadcasts the changes to the live list to all field devices. This allows each field device to maintain a current copy of the live list.
• The linkactive scheduler100/100′ also schedules the communications from other field devices operating in the system. The linkactive scheduler100/100′ coordinates the timing of each communication by issuing compel data messages at the scheduled times. Upon receipt of the compel data message, the requested field device broadcasts or publishes its data to the other field devices operating in the system. To assure proper synchronization, the linkactive scheduler100/100′ also periodically broadcasts a time distribution message on thebus120/120′ so that all field devices have exactly the same data link time. The time distribution message is a message which includes the data link time. The data link time is the system time of the linkactive scheduler100/100′. When the time distribution message is received by thelink masters105/105′ on a given bus, thelink masters105/105′ reset or recalibrate their individual system times to the data link time.
• The remaining operations are performed between scheduled messages or data exchanges. The linkactive scheduler100/100′ grants permission to other field devices to use thebus120/120′ by issuing a pass token message to an individual device. When the individual field device receives the pass token, the field device is allowed to send messages until the field device is finished sending messages or until the maximum token hold time has expired, whichever is shorter. The token hold time is the amount of time the device can send messages after receiving the pass token. This method of control management is commonly called token passing control. A variety of techniques for implementing token passing control are well-known to those skilled in the art.
• To control the data exchanges each device/component preferably includes aninput snap240,processor250,memory255, containedparameters257 andoutput snap260, and amedium attachment unit612, as shown inFIGS. 3 and 8. Theinput snap240 andoutput snap260 protect parameter values from write access or other external interferences during execution of a block. Theprocessor250 processes the execution of stored blocks as well as the algorithms and programs within the blocks. The snapped parameters and containedparameters257 are stored in thememory255. The memory is preferably EEPROM or FLASHROM to permit programming of the device without the danger of losing data due to power loss. In alternative embodiments, thememory255 may be ROM, RAM, or EPROM.
Fieldbus Access Sub-Layer
• Referring again toFIG. 2, the next layer in the communications stack205 is thefieldbus access sublayer220. Thefieldbus access sublayer220 uses the scheduled and unscheduled data exchanges of thedata link layer210 to provide a service for afieldbus message specification230. Again, thissublayer220 is desirably the same in both SIS and non-SIS compatible devices. The service provided by thefieldbus access sublayer220 is the efficient addressing of commonly sent messages. Some examples of fieldbus access sublayer services are called virtual communication relationships (VCRs).FIG. 4 shows three types of VCRs: client/server251,report distribution252, and publisher/subscriber254. Other VCRs may exist, however, in other implementations.
• The client/server VCRs251 are used for operator messages, such as the types of messages listed inFIG. 4. Specifically, client/server VCRs251 are queued, unscheduled, user-initiated, one-to-one communications between field devices and/or components within field devices, including SISCs. Queued means that the messages are sent and received in the order the messages were submitted for transmission without overwriting the previous message. A field device can send a message requesting a data exchange when the field device receives a pass token message from the linkactive scheduler100/100′. The requesting device is called the client. The device that receives the request is called the server. The server responds when it receives a pass token message from the linkactive scheduler100/100′. As is discussed in greater detail hereinbelow, when SISCs are involved in client/server data exchanges, additional message and sender verification techniques, such as those set forth in the SISRP, are used to ensure the proper Safety Integrity Level (“SIL”) is achieved.
• Thereport distribution VCRs252 are used for event notification, such as alarm notifications to operator consoles and trend reports. Specifically, the report distribution VCRs are queued, unscheduled, user-initiated, one-to-many communications. Thereport distribution VCRs252 allow a device to send a message to a common address, such as “ALL OPERATOR CONSOLES.” Desirably, report distribution VCRs for SISCs and non-SISCs are identical. It is to be appreciated that SIL considerations commonly do not arise with respect to reporting events because of the built-in safeguards present in SIL compatible components, namely, their pre-programming to accomplish certain “safety” functions or actions when an erroneous condition is detected.
• The publisher/subscriber VCRs254 are used for publishing data. Specifically, the publisher/subscriber VCRs254 are buffered, one-to-many communications. Buffered means that only the latest version of the data is maintained within the network. New data overwrites previous data. For example, a field device can publish or broadcast messages to other field devices on thebus120/120′ when the field device receives a compel data message from the linkactive scheduler100/100′. The publisher/subscriber VCR254 is used by the field devices for scheduled publishing of user layer function block inputs and outputs. The publishing of user layer function block inputs and outputs is discussed in more detail later. As is discussed in greater detail hereinbelow, when SISCs are involved in publisher/subscriber data exchanges, utilize additional message and publisher verification techniques, such as those provided in the SISRP, are used to ensure the proper Safety Integrity Level (“SIL”) is achieved.
Fieldbus Message Specification (“FMS”)
• Another layer in the communications stack205 is the fieldbus message specification (“FMS”)230. TheFMS230 allows function block applications to send messages to each other using a standard set of message formats. TheFMS230 describescommunication services270, message formats and protocol behavior needed to build a message for theuser layer240, as illustrated inFIG. 5. The formatting of FMSs is defined by a formal syntax description language calledAbstract Syntax Notation1 developed by International Telegraph and Telephone Consultive Committee. Otherwise, the format of FMSs are defined using commonly known message descriptive languages.
• Data that is communicated over thebus120/120′ can be described by an object description. As illustrated inFIG. 6, objectdescriptions280 are collected together in a structure called anobject dictionary281. Theobject descriptions280 are identified by anindex number285. An index number is a cross reference to the location where a particular object description is stored in memory. Index zero287, called the object dictionary header, provides a description of the dictionary itself and defines the first index for the object descriptions of thefunction block application440.
• For example, index numbers1-255 can define standard data types, such as Boolean, integer, floating point, bit string, and data structures, that are used to build allother object descriptions280. The index numbers aboveindex number255 cross reference user layer objectdescriptions280.
• Thecommunication services270, shown inFIG. 5, provide a standardized way foruser layers235/235′, both SIS and non-SIS compatible, to communicate over the fieldbus. Some examples ofcommunication services270 are context management service, object dictionary service, and variable access. The context management services are used to establish and release virtual communication relationships with a virtual field device. The object dictionary service allows theuser layer235/235′ to access and change the object descriptions in a virtual field device. The variable access services allow theuser layer235/235′ to access and change variables associated with an object description.
• In addition, thecommunication services270 enable thefieldbus message specification230 to communicate with thevirtual field devices310,400 in theuser layer235/235′. As shown inFIG. 7A, a field device will have at least two virtual field devices, a network and system managementvirtual field device310 and a uservirtual field device400.
• The network and system managementvirtual field device310 typically storesnetwork management data320 andsystem management data330. The network management data includes a network management information base (NMIB) objectdescriptions portion322 and a NMIBobject data portion325. Thesystem management data330 includes a system management information base (SMIB) objectdescriptions portion332, and a SMIBobject data portion335. The uservirtual field device400 includesblock object data327 includingblock object description326.
• The system and network management informationbase object descriptions322,335 describe the system and network format for the system and network management informationbase object data325,332.
• Standard communication profiles can also be used to allow field devices to communicate and work together on thesame transmission medium120/120′. The communication profiles used infunction block applications440 can be defined dependent on the field devices category or class. Also, to configure and maintain field devices and their function block application, a common file format is often utilized.
• As shown inFIG. 7B, the combination of thebus120/120′, medium attachment unit612 (FIGS. 8A and 8B),physical layer200,data link layer210 and the communications stack205 are considered to form a “black channel” (as illustrated by the hashed blocks)207. Theblack channel207 provides for a standardized communications network and interconnections between SISCs and non-SISCs without requiring additions, deletions or modifications to the communications protocols and configurations currently being utilized to support communications between non-SISCs in one or more field devices using a fieldbus Architecture.
User Layer
• Theuser layer235 processes the information gathered by the field device operating in the system. As shown inFIG. 2, theuser layer235 is an additional layer added to the OSI model. As shown inFIG. 7A, the user layer is generally composed of a network andsystem management application430 and at least onefunction block application440. Each with its own virtual field device described above.
• Thefunction block application440 defines the field device's functionality. Afunction block application440 includes one ormore resources500/500′, as shown inFIG. 8A for a field device having one or more non-SISCs and as shown inFIG. 8B for a field device having one or more SISCs. A field device may contain resources that include SISCs and non-SISCs. Aresource500/500′ is a logical subdivision within the software and/or hardware structure of a device. Aresource500/500′ has independent control of its operation, and its definition may be modified without affecting related resources.
• Additionally, in SIS components, a SIS sublayer, which provides the SISRP,328, as shown inFIG. 7A, is included in thefunction block application440. This sublayer/protocol328 is discussed in greater detail hereinbelow.
• Referring now toFIGS. 8A and 8B, both non-SISC relatedresources500 and SISC relatedresources500′ can be built of blocks and objects, such as: aresource block510 or SIS resource block (“SISRB”)510′,transducer block520 or SIS transducer block (“SISTB”)520′,function block530 or SIS function block (“SISFB”)530′, trend objects560, view objects565,link object570 and/orSIS link object570′,alert objects585,system time601, function block schedules602, and network traffic. Network traffic includes scheduled and unscheduled traffic. In a SIS device, the resource should contain one or more SISFBs and SISTBs. It is to be appreciated that SISRBs, SISTBs and SISFBs are a few examples of SISCs. Additionally, the SIS resource should be designed to detect faults that occur outside of the resource. A brief description of the blocks and objects used in at least one embodiment is provided below.
• Afunction block530 represents the basic automation functions performed by a resource, such as an analog input, analog output, or proportional/derivative (PD), or any other function required for process or manufacturing control devices. Function blocks530 are designed to be as independent as possible of the specifics of input/output devices and the network.
• In SIS devices, theSISFB530′ is commonly used to publish data to another SISFB as well as non-SIS function blocks designed for use in process applications. However, a SISFB can subscribe to data published by another SISFB in order to ensure compliance with a given SIL. Each SISFB can be identified by a unique profile number. In one embodiment, such profile number is specified by the Fieldbus Foundation. Further, a SISFB enables the distribution of SIS control into and among fieldbus components connected to a fieldbus Architecture. In certain embodiments, SISFBs are limited to a defined set. One such set of SISFBs may include analog input, analog output, discrete input, discrete output, analog voting, discrete voting, lock change, and logic. Similarly, other embodiments may provide for SISFBs being provided in one or all of three classifications such as input function blocks, output function blocks and control function blocks.
• Eachfunction block530/530′ uses input parameters according to a specific algorithm and internal set of contained parameters. Input parameters are structured parameters composed of a value field and a status field. The data type specified for input parameters is dependent on the data type of its value field. The status field is identical for all input parameters. Contained parameters may be used to provide values to the block algorithm. The values of the contained parameters may be set by the manufacturer or as part of the configuration. Generally, the contained parameters may also be set during operation. The input parameters and contained parameters are processed according to the specific algorithm to produce output parameters. The output parameters are available for use within thesame function block530/530′ or by other function blocks530/530′.
• Transducer blocks520/520′ can preprocess and post-process data between the function blocks530/530′ and field devices, such as sensors, actuators, and switches. Transducer blocks520/520′ can control access to the input/output devices through a device independent interface used byfunction blocks530/530′. Transducer blocks520/520′ can also perform functions, such as calibration and linearization. SISTBs are desirably designated by a unique profile number, such as one assigned by the Fieldbus Foundation. Further, transducer blocks520 may receive inputs from non-SISFBs and/or SISFBs. However,SISTBs520′ desirably may only receive inputs from other SISCs, such as SISFBs, SIS resource blocks, and/or other SIS compatible blocks.
• Also, since a SISFB can not assume that an underlying system management kernel (“SMK”) is fault free, since the SMK is part of the black channel, the SISFB may include a parameter which functions as a watchdog timer. Such watchdog timer suitably aids in the detection of errors in the scheduling of blocks, such as errors arising from the black channel erroneously scheduling a function block. For example, a “period of execution” parameter can be utilized as a watchdog timer. Such parameter desirably can be written by SIS compatible configuration devices. Additionally, each output SISFB can monitor its execution and reset the watchdog timer (period of execution parameter) each time the block executes. More particularly, if the watchdog timer expires or is updated at too fast of a rate, some or all of the outputs for the affected SISC(s) can be set to a safe state. It is to be appreciated that a “safe state” is commonly component and implementation specific.
• As further shown inFIGS. 8A and 8B, aresource500/500′ also commonly includes one or more link objects570/570′. In a non-SIS device, alink object570 exchanges data between function blocks530 within aresource500 or between resources. The data exchanged by thelink object570 can include process data or events. In addition, thelink object570 can exchange trend report data or alert notification data.
• In a SIS device, SIS link objects (“SISLO”) are utilized. In addition to providing the before mentioned functions and capabilities, SISLOs are extended link objects that utilize an extended safety-related protocol, such as the SISRP, which include parameters that specify the mapping between two SISCs, for example, between a SISFB, a SISRB or a SISTB and a host, regardless of whether the SISFBs are located in a host or another field device or component. It is to be appreciated that other mapping between SISFBS, SISTBs, SISRBs, hosts, and non-SISCs may be provided as needed. Such link object mapping parameters enable a subscriber to detect errors that may be induced by an underlying black channel. SISCs can communicate with each other using the SISRP. The SISRP is described in greater detail hereinbelow.
• Aresource block510 enables the hardware specific characteristics of a device to be accessible to the network. The resource blocks510 insulate the function blocks530 from the resource hardware by including a set of implementation independent hardware parameters. In components which contain one or more SISCs, the resource block should be a SIS resource block (“SISRB”)510′ because, as mentioned above, SISCs can be configured (as desired or necessary) to subscribe to information provided only by other SISCs. SISRBs can be designated by a unique profile number, such as one assigned by the Fieldbus Foundation. Also, SISRBs can include a parameter, for example “SIL_LEVEL_SUPPORTED,” that specifies the maximum SIL level of an application in which the component may be utilized.
• View objects565 and trend objects560 provide efficient access to parameter data within afunction block application440. View objects565 allow groups of parameters to be accessed by executing a single communication request. Trend objects560 allow a collection of parameter samples to be reported in a single communications transfer. For example, view and trend objects associated with SISCs may be communicated using normal or “SIS” client-server, publisher-subscriber or other communication mechanisms.
• Alert objects585 support the reporting of events to an interface device and other field devices. Upon detection of a significant event, afunction block530/530′ may send an alert message using analert object585. For example, a significant event can be an event that affects system operation. Function blocks can report their own errors, alerting operators to problems on a “real-time” basis, as desired.
• System time601 is provided by system management to function block applications (i.e., one or more resources)440 for use in synchronizing operations between field devices. Eachdevice100/100′,105/105′,110/110′ keeps itsown system time601. Eachdevice100/100′,105/105′,110/110′ uses its system time to control the execution of its internal function blocks. Time stamping of alarms, events, and trend information can be based onsystem time601 maintained by each device.
• System management coordinates the execution of the function blocks530/530′ according to a system schedule. The system schedule is a list of execution times for function blocks within a device. Additionally, the execution of afunction block530/530′ may also be invoked by the completion of the execution of anotherfunction block530/530′. System management is described in more detail later.
Application Framework
• Once the components (i.e., the blocks and objects) are implemented, they are completed or connected by an application framework. The application framework coordinates the communication between components internally and externally. Internal communication means communication between function blocks530/530′, regardless of whether they are in the same field device. External communication means communication between field devices withfunction blocks530/530′ and field devices without function blocks. Ideally, the connection of these blocks by the application framework results in a modular system allowing the functionality of an application to be more extensible and portable. The functionality is extensible in the sense additional functionality can easily be added to an existing function or component. The functionality is portable in the sense that functionality can easily be moved from one location, device or component in a system to another or even from one system to another.
• FIG. 9 shows some examples of external communications. Specifically,FIG. 9A shows the communication offield devices620 and amonitor device650, atemporary device660, and aninterface device670. Unlike thefield device620, theother devices650,660,670 contain applications which are not implemented as function blocks. Themonitor device650 is connected to the application framework but does not have a network address. A monitor device monitors communications on the network (e.g., a diagnostic tool may be a monitor device). Atemporary device660 supports diagnostics and adjustment of parameter values. Aninterface device670 provides an operator interface, control applications, and/or configuration and diagnostic support.
• Similarly,FIG. 9B shows an example of external communications which may be supported between aSIS control subsystem910, such as one which might exist onbus120′, and anon-SIS control subsystem920, such as one which might exist onbus120. In this illustrative example, SIS control subsystem includes two SIS devices,SIS Device A930 andSIS Device B940, andnon-SIS control subsystem920 includes two non-SIS devices,Device C950 andDevice D960. ASIS Application A970 is implemented between Devices A and B,930/940, using SISCs. Additionally, anon-SIS Application B980 is implemented between Devices C andD950/960, using, among other things, non-SISCs such as standard function blocks, transducer blocks, resource blocks and link objects. Communications between SIS Devices A andB930/940 and non-SIS Devices C andD950/960 are also supported using common function, transducer and resource blocks, link objects, view objects, alert objects and otherwise. As mentioned previously above, SIS Device A (or B) may publish information to SIS Device B (or A) and to non-SIS Devices C and D. However, non-SIS Devices may only publish information to non-SIS Devices. Desirably, when an implementation such as the one shown inFIG. 9B is first implemented, SISCs in the fieldbus devices/components are tested and registered with a suitable testing facility, such as one provided by the Fieldbus Foundation, to ensure interoperability between SIS and non-SIS fieldbus devices using standard function blocks and/or SISCs.
• Further, write access to SISCs (e.g., SISFBs, SISTBs, and SISRBs) may be restricted to a list of interface devices. The list is desirably pre-configured in the device by a configuration system. The SISCs only grant write access to this list of devices. The write access for SISCs may also be “locked” or similarly configured to prevent the changing of any safety related parameters while the SIS device or SISC is online or in an otherwise undesirable condition (for example, during certain potentially human or equipment hazardous maintenance procedures). Desirably, an alert is generated to an operator whenever a write status is changed. Also, each connection between SISCs is identified by a Connection Key (“CK”). CKs are described in greater detail hereinbelow. Further, the Protocol Data Unit (“PDU”) containing the data written or read to a given SISC is extended to include an authenticator, such as a Cyclic Redundancy Check (“CRC”). A 32 bit CRC can be used to authenticate the validity of data communicated over a black channel by calculating the CRC using the transmitted data, a connection key and other information, as is described in greater detail hereinbelow. CRCs and the calculation of CRCs are well known in the art. Further, it is to be appreciated that CRCs equal to or greater than 32 bits may be utilized in conjunction with the various embodiments to authenticate data transfers atSIL 1,SIL 2,SIL 3 and/or higher levels.
• CRC-32 can be used to detect and protect against corrupted messages, addressing failures, such as masquerading, and expansion of a message. The CRC-32 may also be utilized to protect other commonly known in the art errors or invalid messaging conditions.
• In addition to external and internal interactions, a variety of other possible interactions are well known to one of ordinary skill in the art. For example, there may be interactions with configuration applications, interactions with a human interface application, interactions with other control applications, interactions for the establishment of function block links, interactions with other resources, interactions with system management, and many more.
Function Block Application Structure
• As stated above, afunction block application440, for both SIS and non-SIS devices, defines the functionality of the field device, and includes one ormore resources500/500′. A resource is a logical subdivision within the software and/or hardware structure of the device. Although not shown,function block applications440 are generally implemented using multiple resources. As shown inFIGS. 8A and 8B, theresources500/500′ which make up afunction block application440 may be modeled as a set of SISCs (i.e., blocks or objects) coordinated to execute a related set of operations.
• A block is a logical processing unit of software comprising a named copy of the block and parameter data structure specified by function type. A named copy of the block is an encapsulated software processing unit, such as an algorithm or computer program. The block is encapsulated to create a modular system with the flexibility for upgrades or improvements. The software processing unit can include a computer program and parameters. The software unit is designed to be independent of other blocks and perform a function which can be used in many different function block applications.
• A block is identifiable by its class or subclass. The class of a block indicates its parameters, and how the parameters affect the execution of the software processing unit. A block class specifies the common attributes shared by all instances of the class, including block elements (e.g., input and output events, contained parameters, and common function) and association with resource function (e.g., alarm notifier and function block services). Each block subclass assumes all the parameters specified by the class, as well as the additional parameters attributed to the subclass.
• Block classes can be classified as elementary or composite. A composite block class is one whose algorithm requires the invocation of functions and/or component blocks of the composite block. An elementary block has a fixed algorithm and does not require the use of component functions or function blocks. Specific examples of elementary and composite blocks are described in detail later.
Function Block Application Hardware
• Each device can contain at least onefunction block application440. To execute thefunction block application440, a device usually contains aninput snap240,processor250,memory255,output snap260, andexecution control265, as shown inFIG. 3, as well as the communications stack205 andmedium attachment unit612, as shown inFIGS. 8A and 8B.
• Themedium attachment unit612, such as a network adapter, receives signals from other devices over thetransmission medium120/120′ and translates the signals into a message for theprocessor250. For example, themedium attachment unit612 converts or translates a message from theprocessor250 into a signal for transmission over thetransmission medium120/120′, or a signal from thetransmission medium120/120′ into a message for theprocessor250.
• Theinput snap240,processor250,memory255, andoutput snap260 are for executing the transducer blocks, function blocks, and resource block within a function block application. Specifically, theinput snap240 receives and holds input parameters. These input parameters may be constant or received from other function blocks. Theprocessor250 executes or processes a software program or algorithm based on these input parameters and any contained or stored parameters. These parameters are discussed in more detail below. Theprocessor250 can be, for example, a microprocessor or programmable logic array. Any software programs or parameters used by theprocessor250 can be stored in thememory255, which is preferably EEPROM or FLASHROM. The functionality of thefunction block application440 can be limited, however, by the size of thememory255 and the processing speed of theprocessor250. The output of theprocessor250 is sent to anoutput snap260.
• Theinput snap240 andoutput snap260 are responsible for protecting parameter values from external interferences, such as write access, while theprocessor250 is executing. In other words, once theprocessor250 begins processing the inputs, theinput snap240 andoutput snap260 hold the inputs and outputs constant until the processing is complete.
Parameters
• Parameters define the inputs, outputs, and data used to control block operation. The parameters are accessible over the network.
• An input parameter obtains its value from a source external to the block. An input parameter may be linked to an output parameter of another block within itsresource500/500′ or within another device. An input parameter is an input variable or constant which is processed by the algorithm or program of afunction block530/530′.
• An output parameter is a parameter which may be linked to an input parameter of one or more blocks. Output parameters contain both value and status attributes. The output status attribute indicates the quality of the parameter value generated.
• A contained parameter is a parameter whose value is configured, calculated, or set by an operator or higher level device. In one embodiment, a contained parameter cannot be linked to another function block input or output, and therefore may not contain status attribute.
Parameter Identifiers
• Each parameter can be characterized by its identifiers, storage, usage, and relationship to other parameters. Each parameter can be characterized by more than one identifier. For example, a parameter within a block is uniquely identified by its parameter device identification, and a parameter within a system is uniquely identified by its device identification and tag. Tags can provide a unique symbolic reference to each block within the system.
• The data type for a parameter is specified by its data type index. The data type index is the object dictionary index of the data type. The data type index specifies the machine independent syntax of the parameter. Commonly, the machine independent syntax of the parameter is an abstract syntax. Theuser layer235 encodes/decodes the data according to the transfer syntax rules in thefieldbus message specification230. Additionally, a variety of other parameters may also be stored in theobject dictionary281 and referenced by its object dictionary index number.
Parameter Storage
• Parameter attributes can be classified as dynamic, static, or nonvolatile. Dynamic parameters are values calculated by the block algorithm and, therefore, do not need to be restored after power failure.
• Static attributes are a specific, configured value that must be restored after a power failure. Aninterface device670 ortemporary device660 may write to static parameter attributes on an infrequent basis. Static parameter attributes can be tracked by a configuration device.
• Non-volatile parameter attributes are written on a frequent basis and the last saved value must be restored by a device after power failure. Since the values of these parameter attributes are constantly changing, the values can be tracked by a configuration device.
Parameter Relationships
• The execution of a block involves input parameters, output parameters, contain parameters, and the algorithm or computer program stored within the block. The execution time for a block's algorithm is defined as an attribute of the block. The length of execution time is dependent on the hardware and software implementation.
• In simple blocks, input parameters are received before block execution. When the block begins execution, the input values are snapped to prevent them from being updated while they are used by the algorithm.
• However, before these input parameters are processed, the input parameters are used to determine if the algorithm can achieve the desired mode. A function block application can achieve a variety of modes, such as out of service (O/S), initialization manual (IMan), local override (LO) manual (Man), automatic (Auto), cascade (Cas), remote-cascade (RCas) and remote output (ROut) mode. The out of service, initialization manual, and local override modes are described below. For SISFBs, desirably, input function blocks, such as analog input or discrete input, support modes O/S and Auto. Similarly, for output function blocks, modes O/S, Cas and LO can be supported.
• When a block is in OS mode, the block is not being evaluated, and the output is maintained at the last value.
• When a block is in the IMan mode, the block output is being set in response to the back calculation input parameter status. When the status indicates there is no path to the final output element, then the control blocks initialize to provide for bumpless transfer when the condition clears. A back-calculation output parameter is supported by all output and control class function blocks. The set point may be maintained or, optionally, initialized to the process variable parameter value.
• The LO mode applies to control and output blocks that support a track input parameter. The LO mode may be enabled by a local lock-out switch on the device or a variety of other ways. In the LO mode, the block output is being set to track the value of the track input parameter. The set point may be maintained or, optionally, be initialized to the process variable parameter value.
• The determination of whether the block is able to achieve the desired mode is made by comparing the actual mode attribute and the target mode attribute. The actual mode attribute reflects the mode of operation which the block is able to achieve. The target mode attribute indicates what mode of operation is desired for the block. The target mode is usually set by a control application or by an operator through a human interface application.
• Once the actual mode is determined, the block execution progresses and the outputs are generated. If alert conditions are detected, alarm and event output parameters are updated for reporting by an alert object. When the execution is complete, the outputs are snapped making them available for external access. Prior to being snapped only the previous values are available for external access.
Resource Components
• As stated above, afunction block application440 contains one or more resources, and aresource500/500′ includes one or more blocks. A block is identifiable by its class or subclass. The class of a block indicates its parameters, and how these parameters affect the execution of its algorithm or program. The Resource Components Section provides the formal models for the preferred classes. Preferred classes include a resource class, directory object class, block object class, parameter object class, link object class, alert object class, trend object class, view object class, domain object class, program invocation object class, and an action object class. In alternative embodiments, someone skilled in the art could define a system with more, less, or different classes. Again, domain object, program-invocation objects and action objects are not supported in SISC.
Resource Class
• The resource class defined in a preferred embodiment specifies the descriptive attributes of the resource. The object dictionary of each resource contains a description of the components contained within the resource. The resource class includes the following attributes: resource name, vendor name, model name, revision, logical status, physical status, object dictionary and, in SIS devices, the SIL level supported by the device.
• The vendor name identifies the vendor of the software and/or hardware associated with the resource. The model name specifies the model of the software and/or hardware associated with the resource. The revision attribute is the revision level of the software and/or hardware associated with the resource. The logical status attribute contains information about the communication functionality associated with the resource. The physical status attribute gives a coarse summary of the hardware component associated with the resource. The object dictionary contains the attributes of an object dictionary directory object, resource block, and other objects specific to thefunction block application440 process. Each of these attributes are accessible through thefieldbus message specification230.
• These attributes and the attributes defined for any class or subclass are only illustrative of the attributes that could be used. In alternative embodiments, the resource class or any other class or subclass could include more, less, or different attributes. This concept applies to all of the classes and subclasses described in this specification.
Directory Object
• A directory object acts as a guide to other blocks and objects within a resource orfunction block application440. The directory object contains a list of references to the other blocks and objects making up a resource orfunction block application440. This information may be read by an interface device or temporary device desiring to access objects in the object dictionary. The directory object class is defined as including the following attributes: member identification; starting index of the static object dictionary; data type; sub-index entries; data length; usage; storage; list of valid values; initial value; and item identification.
• The member identification attribute is the unique number which identifies the function of the directory. The index is the index of the directory object in the object dictionary. The various data types include meta type or type name. Meta type indicates the object type. Type name specifies the name of the data type of the object. The sub index entries allow the attributes of a directory object to be accessed individually through the read and write service. The data length attribute specifies the number of bytes reserved to represent the sub index values in the directory. The usage attribute indicates that this is a contained object and may not be referenced by link objects for connection to function block parameters. The storage attribute indicates whether the parameter is stored in static memory. The list of valid values specifies the values permitted for the sub index attributes of the directory object. The initial value specifies the initial value assigned to the sub index attributes of the object directory, and the item identification identifies the description of the object.
Block Object
• The block object class specifies the characteristics common to the function blocks, transducer blocks, and resource blocks. In the object dictionary, parameters follow continuously after the block object, each having an index. The block object class is defined by the following attributes: member identification; block index; data type; sub index; data length; usage; storage; list of parameters; list of valid values; and item identification. The member identification identifies the function of the block. The block index is the index of the block object in the object dictionary. The data type includes the meta type and type name. The meta type indicates the object type. The type name specifies the name of the data structure of the block. The sub index includes attributes, such as block tag, member identification, item identification, revision, profile, profile revision, execution time, period of execution, number of parameters, next block to execute, starting views, number ofview 3 objects, and number ofview 4 objects. The data length attribute equals 62. The list of parameters includes static revision, tag description, strategy, alert key, mode, and block error. The remaining attributes were described above.
• The three sub-classes of the block object class used in a preferred embodiment are resource block objects, transducer block objects, and function block objects.
Resource Block Object
• The resource block object defines hardware specific characteristics of its associated resource. Because the resource block object is a sub-class of the block object model, the resource block object assumes the list of parameters attributed to the block object, as well as its own additional attributes. The additional attributes in the resource block subclass are: resource state, test, resource, additional contained parameters; execution time=0, period of execution=0, and the next block to execute=0.
• A resource block insulates the function blocks from the physical hardware by containing a set of implementation independent hardware parameters. The resource block is manufacturer specific; and all its parameters are defined as contained.
Transducer Block Objects
• Transducer block objects are defined to decouple function blocks from the local I/O functions required to read sensor hardware and command hardware. The transducer block can execute as frequently as necessary to obtain data from sensors without burdening the function blocks that use the data. The transducer block also insulates the function block from the manufacturer specific characteristics of an I/O device.
• The transducer block object is a subclass of the block object and assumes all the attributes of the block class. The additional attributes of the transducer block subclass are: additional contained parameters; execution time=0; period of execution=0; and next block to execute=0.
Function Blocks Objects
• Function blocks represent the basic automation functions performed by a resource, such as an analog input or discrete output. Function blocks are the primary means of defining monitoring and control in a function block application. They are designed to be as independent as possible of the specifics of I/O devices and the network. Function blocks work by processing input parameters and inputs from transducer blocks (or other function blocks) according to a specified algorithm and an internal set of contained parameters. They also produce output parameters and output to transducer blocks or the input of other function blocks.
• Based on the processing algorithm, a desired monitoring, calculation or control function may be provided. The results from function block execution may be reflected in the output to a transducer block or to one or more output parameters that may be linked to other function blocks or directly to the device hardware.
• Function blocks are a subclass of the object class. The additional attributes defined in the function block subclass are the sub-index of execution time, period execution, number of parameters, next block to execute, and additional parameters.
• The sub-index attribute defines the attributes of an object which may be individuals accessed through read and write services by using the sub-index number with the object index number. Sub-index numbers are defined based on Meta type.
• The execution time parameter of the function block object denotes the time required for a function block to execute. The execution time may be divided into three components: pre-processing (i.e., snap of parameter values); execution; and post-processing (i.e., block output values, alarm, and associated trend parameters are updated).
• To provide consistent behavior, the block algorithm executed during the execution component is broken down into the following steps. First, the algorithm determines the actual mode attribute of the mode parameter. This calculation will be based on the target mode and the status of attributes of the inputs as described above. Second, the algorithm calculates the set point, if the set point is defined for the function block. The calculation of the set point will be based on the actual mode, set point input parameters, such as cascade and remote-cascade, and any backward path input status. Also, the value of the controlled parameter, process variable, may be used for set point tracking. The resulting set point is shown in a set point parameter. An example of a set point is the temperature setting of a thermostat (e.g., 72°). In other examples, the set point will change frequently.
• Third, the algorithm executes control or calculation of the algorithm to determine the value and status of the output parameters. The conditions which determine the status attribute of output parameters. The value attributes of the block's input parameters and contained parameters, the actual mode, and the working set point are used in this algorithm. Generally, the calculation of actual mode and the use of actual mode in the algorithm account for the status of critical inputs.
• Fourth, the execution phase calculates the output parameters. This step applies only to output blocks, control blocks, and calculation blocks designed to be used in the cascade path.
• The period of execution of a function block is typically scheduled on a periodic basis. The period of execution is user specified based on control or monitoring requirements specific to an application. The system management services coordinate the function block execution. The management information base, which includes the system schedule, is stored in its own resource in the device. The function block period of execution is specified for a block in data link layer time. Through the scheduling capability provided by system management, it is possible to phase or stagger the execution of blocks in a device where their periods of execution time are the same or are integer multiples of each other. System management is discussed in more detail below.
• The “number of parameters” attribute within the function block object is the total number of parameter objects associated with the function block, including the block object.
• The “next block to execute” attribute of the function block object specifies the next function block within a device to execute to achieve minimum delay in execution within a device. If there is no next function block, then the next block to execute is zero. Thus, where multiple function blocks need to execute in series within a device, a user can specify the first function block to execute in the chain. Through the next block to execute attribute, the order of execution can be predetermined.
• The “list of parameters” attribute of the function block object lists the input, output and contained parameters within a function block.
• Based on the common parameters and the behavior, a preferred embodiment also defines the following subclasses of the function block subclass, including: input function block; output function block; control function block; and calculation function block.
• The input function block subclass receives physical measurements or values from transducer block. The input function block subclass includes a simulation parameter by which the transducer value and status may be over-ridden. The input function block's other parameters preferably include: process variable; primary output; channel number; and additional parameters.
• The output function block subclass acts upon input from other function blocks and forwards its results to an output transducer block. The output function block subclass supports the back-calculation output parameter and simulate parameter. The additional output function block attributes are: set point, simulate parameter, cascade input; back-calculation output; remote cascade in; remote cascade out; and channel number.
• The control function block subclass acts upon inputs from other function blocks to produce values that are sent to other control or output function blocks. The additional attributes for the control function block are: primary output; back-calculation; process variable; set point; primary input; cascade input; remote-cascade in; remote-output in; back-calculation output; remote-cascade out; remote-output out; and additional parameters. The additional calculation function block parameters are: back calculation input; back calculation output; and additional parameters.
Parameter Objects
• Parameter objects are defined to allow the function block, transducer block and resource block attributes to be accessed over the bus. The attributes defined in the basic parameter object model are: member identification; parameter index; relative index data type; sub index; data length; units; usage; storage; list of valid values; initial value; and item identification. Not all the parameters listed are required in a particular block. Additionally, several subclasses from the parameter object class can be defined including output parameter objects, input parameter objects, and contained parameter objects.
Link Objects
• Link objects570/570′ provide mapping between resources and the information exchanged via a communication network as illustrated inFIGS. 8A and 8B. Process data and events to be exchanged between function blocks within a resource or between resources may be defined through link objects. In addition, the communication exchange for support of trends and alerts may be defined using link objects.
• Link objects570/570′ are defined in field devices associated with the function block applications process. Link objects570/570′, by referencing the appropriate VCR, may be used to access, distribute or exchange individual objects. In addition, the link objects define the association between input and output parameters, and trend reports, which interface devices must receive.
• In SIS implementations, an extended safety/SISRP is utilized. The SISRP provides for authentication of communications between SISCs such that SIL-3 and SIL-2 may be attained. In particular, the SISRP protects against errors that may arise during use of the black channel. Such errors may include: transmission bit failure, such as when a single or multiple bit(s) in a message changes state on the black channel; retransmission, where the black channel inadvertently retransmits a message; omission, where the black channel loses a message(s); insertion/expansion, where a message is erroneously generated and/or inserted or expanded on the black channel; wrong order, where the black channel delivers messages in the wrong order; delay, where the black channel delay transmission or reception of a message for a period of time; masquerading, where the black channel delivers messages to the wrong endpointor multiple devices have the same network address; queuing fault, where the black channel delays a message by more than the transmission rate but less than the time delay needed to cause a timeout; communication and function block scheduling errors; system and configuration management errors; and others.
• One mechanism by which the SISRP protects against the before mentioned errors is by utilizing a sequence number. A sixteen (16) bit number can be utilized for each VCR connection to identify a sequence of messages sent between a sending SISC and a receiving SISC. The receiving SISC maintains a corresponding index number. When operating properly, the index number updates at both the sender and receiver with each message sent. When the maximum number of messages is received, the numbers wrap and begin counting up from zero (0) again. Assuming a message transmission rate of a message every ten milliseconds, which is achievable using a High Speed Ethernet connection, the sequence numbers should wrap every 655 seconds. At lower message transmission rates, the sequence numbers will wrap less often.
• If the sent sequence number and the expected sequence number (i.e., the sequence number expected at the receiving component) do not match, then the data is considered “stale” or unusable. If such a stale data condition repeats itself a given, configurable, number of times, then a link between the components may be set as being bad. Such sequence numbers and the link generally, will then need to be reset before communications between the effected components are resumed. Further, in a publisher-subscriber relationship, the sequence number desirably is reset on both the sender and the receiver whenever two correct consecutive messages have been received. For a client-server relationship, if the sequence numbers are out of synchronization, then the connection is aborted and the sequence numbers are reset upon the connection being reestablished. However, in other embodiments, sequence numbers may be reset using other processes and techniques.
• Further, by utilizing a sequence number in the SISRP, protection is provided for retransmission, wrong order and insertion/expansion errors. Additionally, sequence keys are also used in conjunction with CKs in the SISRP to protect against masquerading errors.
• As mentioned above for SIS implementations, connection keys (“CKs”) are desirably utilized. Such CKs are a part of the SISRP and are commonly provided as a parameter in SISLOs. The CK is a unique key that is assigned by a configuration system for connection between an interface device and SISCs (i.e., SISFBs, SISTBs and SISRBs) for client-server connection. Also, a unique CK is assigned for each publisher-subscriber connection, wherein all subscribers to a given publisher are desirably configured to use the publisher's key. The utilization of CKs and sequence numbers in client-server and publisher-subscriber connections is further described in greater detail hereinbelow.
• Also, for SIS implementations the SISLOs can include a SIS Access parameter. This parameter, when set, specifies that read and write requests are processed using the extended SISRP.
Alert Objects
• Alert objects are used to communicate notification messages when alarms or events are detected. An event is an instantaneous occurrence that is significant to scheduling block execution and to the operational view of afunction block application440. An alarm is the detection of a block leaving a particular state. The alert object class allows alarms and events to be reported to a device responsible for alarm management.
• Based on the type of alarm and event information which may be reported by blocks, the preferred embodiment designates three subclasses of alarm objects. They are analog alerts, discrete alerts, and update alerts. Analog alerts are used to report alarms or events whose values are associated with a floating point. Discrete alerts are used to report alarms or events whose associated value is discrete. Update alerts are used to report a change in the static data of a block.
Trend Objects
• Trend objects support management and control of function blocks by providing visibility into history information for reviewing their behavior. Based on the type of information collected, a preferred embodiment defines three subclasses of trend objects. These subclasses are the trend float subclass, the trend discrete subclass, and the trend bit string subclass. The trend float class collects the values and status of floating point input and output parameters. The trend discrete subclass collects the values and status of discrete input and output parameters. The trend bit string subclass collects the values and status of bit string input and output parameters.
View Objects
• View objects support management and control of function blocks by providing “visibility” into their configuration and operation. In other words, view objects allow the user to monitor or “view” data associated with operation, diagnostic, and configuration of the system, functionsblock application440 orresource500. In one embodiment, there are four sub-classes of the view object class. These subclasses areview 1,view 2,view 3, andview 4.View 1 allows access to dynamic operation parameter values.View 2 allows access to static operation parameter values.View 3 allows access to all dynamic parameter values.View 4 allows access to other static parameter values.
Domain Objects
• For a non-SIS device, adomain object580 supports download services that may be used to load data from a client into the server's domain. Data from the server's domain may be transmitted to a client through domain upload services. The domain objects are part of memory. They may contain programs or data. Domains with code and data are combined into an executable program using a program invocation object.
Other Objects
• For a non-SIS device, aprogram invocation object590 provides services to link domains to a program, to start this program, to stop, and to delete it. Action objects may optionally be supported by a resource in a non-SIS device. Through an action object, an individual block or object within a resource may be deleted in the non-SIS device. For SIS devices, action objects commonly are not supported because it is commonly undesirable to delete safety critical or important blocks or objects.
Function Block—Mapping
• For implementation of afunction block application440, thefunction block application440 is mapped into the virtual field device of thefieldbus message specification230, as shown inFIG. 7A. The virtual field objects which are the preferred tools in describing afunction block application440 are: variable objects; event management objects; domain objects (in non-SIS devices only); and program invocation objects (in non-SIS devices only).
• Variable objects are a type of block parameter. Other types of block parameters are simple, array, or record. Record objects support trend, action, and link objects. Grouping of information for access may be done using variable list objects.
• Event notification objects are used for alarm and event notification. Domain objects, which preferably are not available in SIS devices, are a computer program that may be loaded into memory using the domain download services. Program invocation services, which preferably are not available in SIS devices, may control function block application initialization. Such services include: to start, to stop, and to reset.
• The table below is used to show how the function block application model may be mapped directly into the objects defined in the object dictionary.

• Function Block Model	Mapping to FMS

  Resource		VFD
  Directory		Directory Object	Array
  Block		Record
  	Parameters		Simple Variables,
  			Array &Records
  	Views		Variable Lists
  Link Object		Record
  Alert Object		Event
  Trend Object		Record
  Program Invocation		Program
  		Invocation
  Domain		Domain
  Action		Record

• To coordinate the mapping of the function block models into the object dictionary, the device description language (described in more detail later) can be used to describe the function block and support block parameters used by the configuration tool. Such a description is known as a “device description.” In many cases, the “device description” is used in the configuration and interface stations. However, in some cases, all or part of the device description may be stored in the field device. When the device description is stored in the field device, it may reside in its own object dictionary in a resource separate from that used for the function block application. To access the device description information, each block maintains an associated device description reference number.
• The virtual field device collects the blocks and objects discussed above into an object dictionary. Within the object dictionary, each block or object is addressed by an index number and identified by an object description. The object descriptions generally contain an index, object code, further object attributes, and system-specific references to the real object.
Index Numbers
• Index numbers can be grouped according to their data type or structure, or whether the object is static or dynamic. Object indices1-255 can be reserved for commonly used data types and data structures. As shown in the table below, indices1-14 and21 are defined data types in thefieldbus message specification230, and indices64-86 are commonly used data structures, which are referenced in the definition of record objects. These indices are the same as theindex numbers285 shown inFIG. 6.FIG. 10 illustrates how these index numbers can also be grouped by whether the object is static or dynamic.

• Index	Type	Nam

  1	Data	Boolean
  2	Data	Integer 8
  3	Data	Integer 16
  4	Data	Integer 32
  5	Data	Unsigned 8
  6	Data	Unsigned 16
  7	Data	Unsigned 32
  8	Data	Floating Point
  9	Data	Visible String
  10	Data	Octet String
  11	Data	Date
  12	Data	Time of Day
  13	Data	Time Difference
  14	Data	Bit String
  21	Data	Time Value
  64	Structure	Block
  65	Structure	Value &Status - Float
  66	Structure	Value &Status - Discrete
  67	Structure	Value &Status - BitString
  68	Structure	Scaling
  69	Structure	Mode
  70	Structure	Access Permissions
  71	Structure	Alarm - Float
  72	Structure	Alarm - Discrete
  73	Structure	Event - Update
  74	Structure	Alarm - Summary
  75	Structure	Alert - Analog
  76	Structure	Alert - Discrete
  77	Structure	Alert - Update
  78	Structure	Trend - Float
  79	Structure	Trend - Discrete
  80	Structure	Trend - BitString
  81	Structure	FB Link
  82	Structure	Simulate - Float
  83	Structure	Simulate - Discrete
  84	Structure	Simulate - BitString
  85	Structure	Test
  86	Structure	Action - Instantiate/Delete

• All the object descriptions in the object dictionary other than the data type and data structure descriptions may support extensions. For example, the index number of an object description other than a data type or structure may be changed without affecting the other objects. In addition, the object description may also be improved or upgraded without affecting the other objects.
Object Dictionary
• The object dictionary is defined to act as a guide to the information within afunction block application440. Theobject dictionary281 is a list of references to the objects making up that function block application. This information may be read by an interface device desiring to access objects in the object dictionary.
• The object dictionary directory object282 will be defined as the first index in the static object dictionary (S-OD)700, shown inFIG. 10. The starting point of the static object dictionary is defined by the object dictionary object description, which resides in Index Zero. In addition, the object dictionary description identifies the start index, the length of the dynamic list of variable list (DV-OD)710 and the dynamic list of program invocation (DP-OD)720 associated with view objects and program invocation objects.
• The directory can be logically constructed by concatenating the directory objects, and consists of a header followed by the directory entries. An array offset is specified from the start of the logical directory. The logical directory can be thought of as a single array composed of all the directory object instances. The header is commonly present in the first directory object.
• The blocks which reside in a resource are identified in the object dictionary by the directory object. Each instance of aresource block510,function block530, ortransducer block520 consists of a block object and associated parameters. The block object references its associatedview object565.
• The block object is the primary key used in referencing an instance of a block. It identifies the block tag, execution time, profile, and number of block parameters. Also, it identifies the starting location and number of view objects for this block. The parameters of a block are located continuously in the object dictionary following the block object. The block parameter values may be accessed through these parameter objects. Also, the block parameter objects are generally restricted to simple variable parameters, array parameters and record parameters.
• In one embodiment, several data structures have been standardized for the function block application process.
Common Sub-Functions
• This section contains descriptions of sub-functions common to many blocks. A process control function has the following elements: (1) one or more inputs; (2) one or more outputs; (3) scaling information; (4) a mode selector; (5) a selected algorithm; (6) a set of visible data parameters; and (7) a set of internal data. Each of these elements represents either static data or dynamic data. Static data is data which is seldom changed, while dynamic data may change with each block evaluation.
• Each instance of a block is processed according to the algorithm selection at a time determined by a combined block execution and communication scheduler. The scheduling information often contained in the parameters of a block is the period of execution and the maximum execution time.
Connections
• A block input contains the data read from outputs of other blocks. If a block does not receive an input from another block, a constant input can be entered. The permanence of the value depends on the kind of memory to store it. The type of memory used depends on the parameters. For example, volatile memory is sufficient for a frequently changing parameter. Nonvolatile memory can be used, for example, for set points. Block outputs contain the result of block evaluation, or an operator entry if the mode is manual.
• Both inputs and outputs comprise a value field and a status field. The status field contains quality, substatus, and limit attributes. It is the same for all inputs and outputs.
• The input and output function block classes must exchange data with the device hardware and this is completely under the control of the manufacturer who writes the device code, as this data never goes through the communication system. Alternatively, many blocks provide parameters which may be written and read by remote devices operating a proprietary control application. To conduct such an exchange, the remote device must execute a handshaking utilization algorithm before writing or the block may ignore the input.
Simulation
• Input and output class function blocks can have a simulation parameter, which has a pair of status values, and an enable switch. This parameter acts as a switch at the interface between a function block and the associated transducer block or hardware channel. For inputs, the transducer value and status are received from the transducer block or hardware channel if the switch is disabled. When the enable switch is on, the simulation parameter and status values are received from the function block, and the transducer block or input channel is ignored.
• For outputs, the simulate value and the status value become the readback value and status when the enable switch is on, and the transducer switch is ignored.
• Scaling information is used for two purposes. Display devices use the range for bar graphs and trending. Control blocks use the range as percent of span, so that the tuning constant remains dimensionless.
• Further in SISCs, when the write lock in a resource is activated, simulation capabilities are desirably disabled.
Modes
• Blocks can also have a mode parameter which determines the resource of the data to be used for the block's input and output. Blocks are desirably configured to permit the out-of-service (O/S) mode and can support at least one other mode.
• The permitted modes apply to the target mode. A write request to the target mode is rejected if it does not match the permitted list. A configuration device should not allow a mode to be permitted that is not supported. The actual mode is not constrained by the permitted mode, because some modes are acquired for initialization.
Parameter Access Table
• An access table commonly exists for each block. The purpose of that table is to define the relative position of the parameters within each block, and to define the contents of the standard views of the parameters.
• The block parameters which need to be communicated over the bus vary within the application. To allow communications among the various function blocks, predefined sets of variables can be selected for each function block. The parameters included in these predefined sets of function blocks are specified in the views in the parameter access table. If parameters are added to a block, these parameters are added after all the standard parameters.
• The parameter access table provides the following: (1) the order in which the parameters appear sequentially in the object dictionary relative to the location of the associated block object; (2) a list of parameters associated with the function block address in the table; and (3) predefined parameter sets. The predefined parameter sets includeview 1 throughview 4.
• View 1 is the operation dynamic parameter set. The operation dynamic parameter set includes information required by a plant operator to view process control, see alarm conditions, and adjust operating targets.
• View 2 is the operation static parameter set. The operation static parameter set includes information which may be required for display to an operator with dynamic information. This information is read once when the associated display is first caught up, and refreshed if the static update code changes.
• View 3 is the all dynamic parameter set. The all dynamic parameter set includes information which is changing in value and may need to be referenced in a detailed display.
• View 4 is the static parameter set. The static parameter set includes information which is normally referenced during the configuration or maintenance and has a specific value unless changed by an operator or instrument technician.
• The parameters associated with each block are listed in separate access tables. The first six indices are identical, which forms a standard header for all standard and extended function blocks. The remaining indices are for the core parameters of the function and the lesser used parameters. Finally, there are the parameters required for alarm processing, followed by the alarm records.
Other Common Sub-Functions
• In addition to the common functions discussed above, there are many others. These other subfunctions can include, for example: status; back calculation (BKCAL); cascade (CAS); output tracking (TRK); balancing bias or ratio (BIAS or SP); fail safe handling (FSAFE); bad cascade status handling; invalid values; parameters; alarms; and initialization and restart.
Resource Components
• As discussed above, a device commonly includes one or morefunction block applications440. Afunction block application440 includes one ormore resources500/500′, and aresource500/500′ includes one or more blocks/objects. Each resource has a resource block.
• Further, each resource block commonly contains data that is specific to the hardware that is associated with the resource. The data in the resource block is modeled as contained parameters, so there are no links to this block.
• Each function block application also commonly contains at least one function block. Generally, ten function blocks exist which, when combined, can provide the vast majority of functions for manufacturing equipment on a process control system. These blocks are: analog input; analog output; bias control selector; discrete input; discrete output; manual loader; proportional/derivative; proportional/integral/derivative; and ratio. In SIS devices, some but generally not all of these types of function blocks may or may not be supported. For example, available SISFBs can be limited to analog input, analog output, discrete input, and discrete output. Likewise, analog voting, digital voting and other function blocks can be supported. Thus, it is to be appreciated that some, all, none or others of the above identified function blocks can be used and that some of these function blocks may include SISFBs or non-SISFBs.
• In addition, nineteen standardized function blocks commonly are used to perform more complex functions, including advanced control blocks, calculation blocks, and auxiliary blocks. These nineteen function blocks commonly include: pulse input; complex analog output; complex discrete output; step output proportional/integral/derivative; device control; set point ramp generator; splitter; input selector; signal characterizer; lead lag; dead time; arithmetic; calculate; integrator; timer; analog alarm; discrete alarm; analog human interface; and discrete human interface. These blocks address additional requirements for both a low and high speed fieldbus.
• Standard transducer blocks can also be utilized, as desire and/or necessary.
• Examples of two target applications, amanual control760 and a safety-relatedfunction770, using the function blocks are shown inFIG. 11. Themanual control760 consist of an analoginput function block762, amanual loader764, and an analogoutput function block768. The safety-relatedfunction770 consists of a plurality of SIS analog inputs (“SISAI”)772, a SIS analog voter (“SISAVTR”)774, and a SIS digital output (“SISDO”)778.
Device Descriptions (DD)
• As shown inFIG. 12, the function block application processes may also store device descriptions (DD)860. To extend the network's interoperability, thedevice descriptions860 are used in addition to the standard function block parameters. Thedevice descriptions860 extend the descriptions of each object in the virtual field device.
• Thedevice descriptions860 provide information needed for a control system to interpret the meaning of the data in the virtual field device, including the human interface functions, such as calibration and diagnostics.
• The device description can be written in any standardized programming language, such as C, C++, or SmallTalk.
System Management
• In operation, function blocks execute in precisely defined intervals and in proper sequence for correct control system operation. System management synchronizes execution of the function blocks and a communication of function block parameters on the bus. System management also handles other important features such as publication of the time of day to all devices, automatic assignment of device addresses, and searching for parameter names or tags on the fieldbus.
• The configuration information needed by the system management, such as the system schedule, is described by object descriptions. The configuration information is stored in the network and system managementvirtual field device310, as shown inFIG. 7A. The network and system managementvirtual field device310 provides access to the system management information base (SMIB)330, and also to the network management information base (NMIB)320. The system schedules can be inputted manually or built using a schedule building tool. A schedule building tool is used to generate a function block and link active scheduler schedules are used to generate system and network schedules.
• Based on the system schedule, system management controls when the function blocks execute. This insures that each function block executes at the appropriate time in relationship to other function blocks in the system. For a true distributed control system, the activities of the devices and their function blocks also have to be synchronized with those of other devices on the network. The coordination of the execution of blocks in different devices is controlled by a network manager using a network schedule. Network Management is described in detail later.
• The system and network schedules contain the start time off-set from the beginning of the absolute link schedule start time. The absolute link schedule start time is known by all devices on the fieldbus.
• The system management also has a time publisher which, in a linkactive scheduler100, periodically sends application clock synchronization to all field devices. The data link scheduling time is sampled and sent with the application clock message so that the receiving devices can adjust their local application time. Between synchronization messages, the application or system clock time is independently maintained in each field device based on its own system clock. The system clock in each field device initiates the execution of the system schedule for that device, not the data link clock, unless the field device is the linkactive scheduler100. System clock synchronization allows the field devices to stamp data throughout a network. If there are backup system clock publishers on the bus, a backup publisher will become the data link clock if the currently active time publisher should fail.
• System management also automatically assign unique network addresses to each field device. Commonly, every field device, except a temporary device, should have a unique network address and physical tag. Temporary devices commonly are not assigned tags or permanent addresses. Temporary devices simply join the network at one of four data link visitor addresses reserved for them in the data link layer protocol specification.
• The system management function responsible for tag and data link address assignment is referred to as the configuration master. It is normally co-located with the linkactive scheduler100, although it is not required to be, so it can monitor the live list for the addition of new devices. When a device is added at a default network address, configuration master verifies that a system management kernel for the field device does not have a physical tag and assigns it one using system management kernel protocol810. Once assigned, the system management kernel moves to the initialized state. In this state, it is ready to be assigned a network address on the operational network. A system management kernel is described in detail later.
• The sequence for assigning a network address to a new field device is as follows: (1) a physical tag is assigned to a new device via configuration device; (2) system management asks the field device for its physical device tag default network address; (3) system management uses the physical device tag to look up the new network address in the configuration table; and (4) system management sends a special set-address message to the device which forces the device to assume the network address. The sequence of these steps is repeated for all devices that enter the network at a default address.
• FIG. 12 shows a representative relationship between certain system management and the other communication and application components. In particular,FIG. 12 shows the relationships between the system management andfunction block application440, function block objects850, device descriptions (DD)860, and object descriptions (OD)280. System management can use thefieldbus message specification230 to remotely access management information within a field device. System management can also access the communications stack205 to perform its other functions.
• A single system management entity commonly exists in eachlink master105/105′ or linkactive scheduler100. This entity comprises a system management information base830 (SMIB), anobject dictionary280, and asystem management kernel800.
• Thesystem management kernel800 provides a network coordinated and synchronized set of functions. To enforce the coordination and synchronization of these functions across the network, a manager/agent model is used. In a preferred embodiment, thesystem management kernel800 assumes the role of an agent and responds to the instructions received from the system management. A system management protocol is commonly used to define communications between managers and agents.
• Information which is used to control system management operation can be organized as objects stored in theSMIB830. TheSMIB830 is accessed by the network through the system and network managementvirtual field device310. TheSMIB830 contains configuration and operational parameters for a device. Examples of the objects included in theSMIB830 are: device identification, physical device tag, list of virtual field devices, time object, schedule object, and configuration status.
• The system management allows SMIB objects to be accessed using the fieldbus message specification application services, such as read, write, etc. Access to the SMIB allows remote applications to obtain management information from the device, either before or during network operation. The management virtual field device is shared with thenetwork management agent880 of the device and thereby also provides access to network management agent objects.
Network Management
• FIG. 12 also shows the architectural relationship between network management and the other communication and application components in a device. Each device contains a singlenetwork management agent880 and layer management entities (LME)875 for its protocols (one for each layer). Each network has at least one network manager which coordinates the network management of the whole system. Network management provides the capabilities of: loading a virtual communication relationship list; configuring thecommunication stack205; loading the network schedule; performance monitoring; and fault detection monitoring.
• The network manager is responsible for maintaining the operation of the network according to the policies defined for it by the system manager. The network manager enforces the system management policies by monitoring the status of thecommunication stack205 in each device, and taking action when necessary. The network manager performs these tasks by processing information and reports produced bynetwork management agents880, and recommending agents to perform services requested via thefieldbus message specification230.
• Thenetwork management agent880 is responsible for providing the network manager with afieldbus message specification230 interface to manage objects of thecommunication stack205. Internal to the device, thenetwork management agent880 maps fieldbus message specification service requests to objects that it maintains for thecommunication stack205 as a whole, an objects maintained by the LMEs.
• TheLMEs875 provide management capability of a layer protocol, such as the physical layer (PHY)200, the data link layer (DLL)210, fieldbus access sublayer (FAS)220 or fieldbus message specification (FMS)230 (as shown inFIG. 2). TheLMEs875 provide thenetwork management agent880 with a local interface to the managed objects of the protocol. All network access to the LMEs and their objects is provided by thenetwork management agent880.
• TheNMIB895 contains theNMIBs320 in the system and network management virtual field device (VFD)310. The NMIB also contains objects used to define configuration management, performance management and fault management. The objects are accessed by network managers using fieldbus message specifications services. The objects used for network management objects are designed similar to the function blocks described earlier.
Flexible Function Blocks
• For simplicity and illustrative purposes, flexible function blocks (“FFBs”) are described by referring mainly to exemplary embodiments. However, it is to be appreciated that FFBs and safety-related FFBs (“SIS-FFBs”) may be used in other implementations and designs using other distributed control architectures. Further, it is to be appreciated that that principles discussed herein as applying to FFBs and/or SIS-FFBs may also be applicable to other block-oriented implementations, fieldbus Architectures or other process control systems.
Function Block Framework
• With reference toFIGS. 8A and 8B, the open system described above provides a framework for and a detailed description of function blocks530/530′. With reference toFIG. 11, the open system described above provides a framework for and description of the interconnection of function block inputs and outputs to provide an application solution.
• With reference toFIG. 12, described above are device descriptions (DD)860 which may be utilized to describe the input and output parameters of a function block. TheDD860 provides information needed for a control system to interpret the meaning of the function block data, including the human interface functions, such as calibration and diagnostics. As stated above, the device description can be written in any standardized programming language, such as C, C++, or SmallTalk, or a custom designed device description language.
Flexible Function Block—End User Configured Input/Output and Algorithm/Program
• As shown inFIG. 13, one implementation of a SIS-FFB1350 may include end-user configurable SIS-FFB input(s)1351, end user configurable SIS-FFB output(s)1352 and an end user configurable SIS-FFB algorithm (program)1353. The end-user1300 creates the SIS-FFB1350, configuring the input(s)1351, output(s)1352 andalgorithm1353 according to the needs of a particular application and according to particular safety requirements. As described above for a SISFB, the SIS-FFB input parameter(s)1351 define the input(s) that are received by the SIS-FFB1350 and the SIS-FFB output parameter(s)1352 define the output(s) that are generated by the SIS-FFB1350 after the input(s) are processed by analgorithm1353, as specified by the SIS-FFB1350. The SIS-FFB Configuration Tool1301 creates a SIS-FFB device description (DD)1360 that matches the SIS-FFB1350 configured by the end-user. The SIS-FFB Configuration Tool1301 preferably creates the SIS-FFB1350 by generating data files and code files that define the SIS-FFB1350 based on the user-configured input(s)1351, output(s)1352 andalgorithm1353 and by generating a matching device description. Alternatively, the end-user1300 (or a programmer) may generate the data and code files that define the SIS-FFB1350 and the matching device description.
• The end-user creates SIS-FFB1350 and a matching SIS-FFB DD860 by running SIS-FFB Configuration Tool1301. SIS-FFB DD860 enables human interface applications such as operator interface, tuning, calibration and diagnostics to be used with SIS-FFB1350.
• Since the SIS-FFB1350 operates in a function block framework, the end-user configured SIS-FFB inputs and outputs can be interconnected to solve complex application-specific control problems such as discrete/hybrid/batch and PLC control. Any combination of blocks (standardized and flexible, SIS and non-SIS) may generally be used to solve any particular application problem. It is also apparent that interconnection of standardized and flexible blocks applies to high speed connections, such as HSE, and lesser speed connections. As such FFBs and/or SIS-FFBs are generally communications protocol and configuration independent and may operate on any variety of communications channels.
• With reference toFIG. 14, twofield devices620 on abus120′ controlling a process are illustrated. As shown, there are two applications, Application A and Application B, being run by the twofield devices620. The first application, Application A, is a non-distributed application run by the first of thefield devices620. Application A is built by a combination of interconnected SISFB and SIS-FFBs (e.g., SIS-FFB1350). The second application, Application B, is a distributed application run by both of thefield devices620. Application B is also built by a combination of interconnected SISFBs and SIS-FFBs (e.g., SIS-FFB1350). As illustrated byFIG. 14, the SIS-FFB overcomes the limitation of non end-user configurable input/output and non end-user configurable of standardized function blocks. Distributed andnon-distributed applications1360 infield devices620 onbus120 can built using any combination of SISFBs and SIS-FFBs1350. It is to be appreciated that in certain embodiments, significant reductions in plant control system installation, operating and maintenance costs may be achieved using FFBs and/or SIS-FFBs.
• FIG. 15 is a block diagram illustrating an example of a complex application built using a combination of standardized function blocks and FFBs.FIG. 15 is an example of multivariable matrix control for a gas processing plant implemented using FFB-MVMC954.
• The field devices/components (e.g.,PI1,TI1,TI2, TI-3,AI1,AI2,FIC1,FIC2, LIC1) shown inFIG. 15 preferably include standard function blocks. It is to be appreciated, while not shown inFIG. 15, that SISFBs and/or SIS-FFBs may be utilized in such an implementation as particular safety related needs may require.
Extended Safety-Related Protocol
• As discussed above, a SISRP can be used to authenticate and ensure that communications between SISCs have not been corrupted. In one embodiment, the SISRP utilizes sequence numbers and CKs to validate or authenticate messages.
Publisher-Subscriber Communications
• When publisher-subscriber communications are being accomplished, at least one of the various embodiments facilitate secure communications by the process shown inFIG. 16. However, before describing the illustrated embodiment in detail it is to be appreciated that, in general, a CK is associated with each link between SISFBs and/or SIS-FFBs. As discussed above, these CKs are generated by the configuration system and are desirably stored in the resource as part of the publisher-subscriber linkage objects. When data is to be published to a subscriber, desirably the communications include the output parameters (i.e., the data), including value and status information, a sequence number (as described above) and an authenticators (for example, a CRC-32). One embodiment of a process for generating the authenticator is shown inFIG. 16A.
• As shown inFIG. 16A, the process for generating an authenticator for one embodiment that includes obtaining the information utilized to generate the authenticator (Operation1602). This operation includes identifying the publisher and the subscriber so as to specify the connection over which the data is to be communicated (Operation1604). This operation also entails obtaining the data (Operation1606), obtaining the next sequence number used over the identified connection (Operation1608), obtaining the CK associated with the specified connection (Operation1610), and obtaining the object index used to identify the parameter in an FBAP to which the data to be communicated pertains (Operation1612). In one embodiment, the connection key includes four (4) bytes of information, the sequence number includes two (2) bytes, the object index includes two (2) bytes and the data includes anywhere from two (2) to one hundred and twenty (120) bytes of information. Yet, it is to be appreciated that in other embodiments, other lengths for data and/or information may be utilized.
• Once the desired and necessary information is obtained and suitably stored (e.g., in RAM or otherwise) for use by the processor in the publishing device, the process continues with arranging the obtained information into a desired sequence used to generate a Virtual Protocol Data Unit (“VPDU”), which may be subsequently used to generate the authenticator. As shown inOperation1614, one sequence that may be utilized to generate a VPDU is shown. It is to be appreciated that other sequences may be utilized, as particular implementations require or specify. Commonly, however, the sequence utilized to arrange the information and generate the VPDU should be standardized so that any SISC (e.g., a SISFB or SIS-FFB) may authenticate data received from or provided to any other SISFB/SIS-FFB. Thus, the sequence shown inFIG. 16 is a preferred, but not mandatory, VPDU sequence. It is to be appreciated that this sequence is “virtual” because it is not communicated over the black channel to the subscribing device/component.
• Using the sequence of information generated inOperation1614, the process continues with generating the authenticator (“GA”) (Operation1616). It is to be appreciated that any of many well known authenticator generation processes may be utilized. Desirably, an authenticator chosen complies with SIL-3 and/or SIL-2 safety requirements. In one embodiment, CRC-32 algorithms are utilized to generate a CRC-32 authenticator. In other embodiments, CRC-64 or other algorithms may be utilized to generate the authenticator.
• Referring now toFIG. 16B, the process shown inFIG. 16A continues with generating or assembling the Actual PDU (“APDU”), i.e., the data and information that is to be communicated over the black channel from the publisher to the subscriber (Operation1618). As shown inFIG. 16B, the APDU is assembled in the following sequence: thedata1606, thesequence number1608 and the authenticator (GA)1620 (i.e., the result generated in Operation1616). It is to be appreciated, that other sequences may be utilized in other embodiments. However, for purposes of standardized communications on an open fieldbus Architecture or similar architecture, it is desirable for all APDUs to utilize the same data sequences. The APDU is then communicated over the black channel to the subscriber (Operation1622).
• Upon receiving the APDU, the subscriber suitably extracts and stores the received authenticator (“RA”)1620′. It is to be appreciated that theGA1620, as well as thedata1606 and/orsequence number1608 may be corrupted during transmission over the black channel. The subscriber then proceeds with authenticating the received or actual protocol data unit (“APDU”) and determines whether the data in the APDU has been corrupted or is otherwise erroneous due to any of the before mentioned safety considerations (e.g., retransmissions, omissions, bit falsifying, masquerading, and the like). APDU authentication proceeds in the subscriber by generating an expected protocol data unit (“EPDU”) (Operation1623). As shown, to generate the EPDU, the subscriber arranges expected information and received data and information into the same sequence as was used inOperation1614 to generate the VPDU. More specifically, the subscriber obtains, from its memory or otherwise, an expectedconnection key1624 and an expectedobject index1626. These are combined, as shown, with the received sequence number (“RSN”)1608′ and the receiveddata1606′. InOperation1628, the subscriber than calculates the expected authenticator value (“EA”) using, preferably, the same algorithms (e.g., CRC-32) as were utilized by the publisher inOperation1616 to generate the GA (1620).
• Referring now toFIG. 16C, inoperation1630, the EA is then compared to the RA.
• If the EA is not the same as the RA, then the data was somehow corrupted during transmission over the black channel, was sent erroneously by the publisher, or processed erroneously by the subscriber. The APDU is rejected by the subscriber and processing of the APDU is stopped (Operation1632). Further, if a successive number of authenticator verifications fails more than a threshold maximum number of times, then the link between the publisher and subscriber is desirably identified as “bad” and future PDUs are not processed using the “bad” publisher-subscriber link until the “bad” condition is resolved.
• Referring again toOperation1630, if the EA is the same as the RA, then the data and information communicated in the APDU is considered to be authenticated. However, since it is possible for data to be sent from a publisher, without corruption over the black channel, in an incorrect sequence, desirably, the process continues with the subscriber verifying that the data received from the publisher is in the expected and correct sequence. This sequence verification can be accomplished, for example, by the subscriber obtaining the expected sequence number from its VCR (Operation1634) and comparing the received sequence number (“RSN”) to the expected sequence number (“ESN”) (Operation1636). If the RSN is not equal to the ESN, then processing of the APDU stops (Operation1632) and the data is discarded. If the sequence numbers are the same, then message/data processing continues using routine non-SIS message processing routines and procedures. Additionally, the subscriber sets a parameter, the last received sequence number (“LRSN”) variable, equal to the RSN and desirably resets a “stalecount” parameter to a value of zero.
• As mentioned previously, if sequence numbers are incorrect a given number of times (i.e., a “stalecount” exceeds a preset threshold), then the status of the connection between the associated publisher and subscriber is set to “bad” and no future PDUs between the publisher and the subscriber will be accepted until the connection status is reset. In order to recover or restore a “bad” connection between a publisher and a subscriber due to an exceeding of the “stalecount” threshold, for one embodiment, the process continues, commonly after a pause and manual or automatic resetting of the link, when a valid authenticator is received. Since the sequence number sent by the publisher, the RSN, and the LRSN in the subscriber are most likely different, the difference between the RSN and the LRSN is calculated. If this difference exceeds the threshold for the stalecount, then the LRSN is set to the RSN, the stalecount is set to zero (0) and the PDU is discarded. The next PDU received is again processed according to the procedures described inFIGS. 16A-C and normal data processing resumes provided the authenticator and sequence numbers are less than the stalecount threshold.
• While the operations shown inFIGS. 16A-16C set forth one embodiment for authenticating data communicated over a black channel meets certain safety requirements, it is to be appreciated that the operations, data sequences, authentication algorithms and the like may be changed, added to and/or deleted. For example, Operations1630-1636 may be deleted from the processing. Such Operations may be considered to be optional if the RSN utilized to generate the EPDU inOperation1623 is replaced with an ESN. Using such a process flow, it is anticipated that the EA would not equal the RA if any of the bits in the received information were corrupted or otherwise erroneous. However, such a process flow may not be capable of more precisely identifying which types of errors are occurring over the black channel, for example, whether the error due to sequence number problems, corruption of the actual data received, connection key problems or otherwise. As such it is to be appreciated that various process flows, algorithms, operations, PDUs and the like may be utilized to authenticate data communicated between a publisher and a subscriber over a black channel.
• FIGS. 16D,16E and16F show the flow diagram for another embodiment that can be used to secure publisher-subscriber communications. This embodiment utilizes replicated data to provide a further assurance of data integrity. Referring toFIG. 16D, operations1650-1666 are substantially the same as those of Operations1600-1616 (shown inFIG. 16A) and proceed as described above. Once the authentication generation process (Operation1666) is complete, the process continues with generating or assembling an Extended Actual PDU (“EAPDU”) that is to be communicated over the black channel from the publisher to the subscriber (Operation1668). As shown inFIG. 16E, the EAPDU is assembled in the following sequence: thedata1656, thesequence number1658, theauthenticator1670, thedata1656, thesequence number1658 and theauthenticator1670. That is, the EAPDU sequence contains replicated data:RD11692 consisting of thedata1656, thesequence number1658 and theauthenticator1670 andRD21694 consisting of thedata1656, thesequence number1658 and theauthenticator1670. The EAPDU is then communicated over the black channel to the subscriber (Operation1672 as described above).
• Upon receiving the EAPDU, the subscriber proceeds with authenticating the EAPDU and determines whether the data in the EAPDU has been corrupted or is otherwise erroneous due to any of the before mentioned safety considerations. As shown inFIG. 16E, the EAPDU authentication proceeds in the subscriber by comparing, on a bit-by-bit basis, the receivedRD11692 with the received RD21694 (Operation1696). If RD1 is not identical to RD2, then the data is invalid, the EAPDU is rejected by the subscriber, processing of the EAPDU is stopped (Operation1682) and the stale count is incremented. Otherwise, EAPDU authentication continues with the subscriber generating an expected extended protocol data unit (“EEPDU”) (Operation1673). The EEPDU is generated by the subscriber obtaining an expectedconnection key1674 and an expectedobject index1676 as previously described. These are combined, as shown, with the receivedsequence number1658′ and the receiveddata1656′ (which may be obtained from either RD1 or RD2. The subscriber then calculates the expected authenticator value (“EA”) (Operation1678) as previously described above. The EA is then compared to the received authenticator (“RA”) which has been suitably extracted from either RD1 or RD2. If the EA is not the same as the RA, the data is invalid. The EAPDU is rejected by the subscriber, processing of the EAPDU is stopped (Operation1682) and the stalecount in incremented.
• Referring again toOperation1680, if the EA is the same as the RA, then the authentication process continues with the subscriber verifying that the data received from the publisher is in the expected and correct sequence by comparing the received sequence number (“RSN”) to the expected sequence number (“ESN”) obtained from its VCR (Operation1684). If the RSN is not equal to the ESN, then processing of the EAPDU stops (Operation1682), the data is discarded and the stalecount is incremented. If the sequence numbers are the same, then message/data processing continues using routine non-SIS message processing routines and procedures. Additionally, the subscriber sets LRSN equal to the RSN and desirably resets the stalecount to a value of zero.
• If thedata1656, theauthenticator1670 or the sequence numbers are incorrect a given number of times (i.e., the stalecount exceeds a preset threshold), then the status of the connection between the associated publisher and subscriber is set to “bad” and no future PDUs between the publisher and the subscriber will be accepted until the connection status is reset as previously described above.
• Further, it is to be appreciated that by authenticating data communicated over the black channel for use by safety related components, the various embodiments of the invention described herein may also be utilized to verify the operational status of a black channel for non safety related devices. In particular, if repeated errors occur over a black channel between safety related devices, the probability of errors for non-safety related devices occurring is probably increased. As such, by monitoring the rate and number of authentication failures for safety related communications, one may also indirectly monitor the overall status of the black channel for all communications.
Client-Server Communications
• In addition to supporting publisher-subscriber communications, client-server communications between SISCs can be supported. As is commonly appreciated, client-server communications commonly involve read operations and write operations. Processes, systems and devices for implementing safety-related read and write processes are described hereinbelow.
Read
• In general, a read utilized to read data utilized in a SIS device (i.e., one with SISCs) is similar, and in certain embodiments identical, to the reads utilized in non-SIS devices (i.e., those without SISCs).
• As shown inFIG. 17A, the process by which a component responds to a read request commonly begins with a response by the server (i.e., the component providing the requested information to the requestor/client) of a request to obtain or “read” certain blocks (i.e., output values) provided by the device. Such blocks are commonly identified by an index number or other identifier (Operation1702). As is commonly appreciated, a device may be capable of outputting many blocks, some of which may be SISCs. As such, the process suitably continues with determining whether the read involves a safety related block (Operation1704).
• If the read does not involve a SISC, then processing desirably continues using standards non-SISRPs (Operation1706).
• Referring again toOperation1704, if the read involves a SISC, for example, one which includes a safety parameter such as SIS_Access or the like, then processing continues using the SISRP. As discussed previously with respect to publisher-subscriber communications, the SISRP, in at least one embodiment, provides for the calculation and transmission of an authenticator over a black channel. In client-server communications, which involve SISCs, an authenticator is used in transmitting the desired information. As shown in Operations1708-1744 (FIGS. 17A-C), the process for generating an authenticator, transmitting the requested read data, and authenticating the transmitted data is substantially the same as that used in transmitting data for publisher-subscriber communications. However, an optional andadditional sub-index1717 may be included in the information utilized to generate and verify the authenticator. Further, if the received sequence number is not equal to the expected sequence number then, for at least one embodiment, the PDU is discarded.
• FIGS. 17D-17F show the flow chart of another embodiment of the SISRP that provides for the replication of data transmitted over a black channel in client-server communications between SISCs. As shown in Operations1750-1799 (FIGS. 17D-F), the process for generating an authenticator, replicating the data, transmitting the requested read data, and authenticating the transmitted data is substantially the same as that used in transmitting the extended data for publisher-subscriber communications.
Write
• When write processes are desired for SISCs, desirably the SISRP, as discussed above, is utilized. To ensure that the receiver of the “write” data and information first verifies the received data and information, the SISRP includes an authenticator and sequence number in any communications. This process can be accomplished, for example, by comparing the length of the data to be written (as specified, for example, in the FMS) against the length of the actually received data string. If such data string does not have a valid length, the data string is discarded. If the data strength has a valid length, then the authenticator is validated, preferably using the processes previously discussed above with respect to publisher-subscriber communications. Further, once the authenticator is validated, the write operation then proceeds. However, if the resource block associated with the block receiving the write request (i.e., the server) is not in an OSS state or a Manual state, then desirably the write request is discarded. It is to be appreciated that it is generally undesirable to write to parameters utilized by SISCs when a safety related resource is being utilized.
• Additionally, under certain conditions, it may be desirable to write data into a SISLO. Since sequence numbers are not provided for SISLOs, the write to a SISLO suitably proceeds with calculating an authenticator without including a sequence number. Otherwise, processing of “writes” for SISLOs proceeds as discussed hereinabove for SISCs.
Additional Safety FeaturesAuthenticator Error Detection
• In addition to the use of the SISRP and the other features and functions discussed hereinabove, authenticator error detection may also be provided. For example, the number of authenticator errors that are generated over a period of time can be monitored. For components used in SIL-3 applications, desirably an error rate greater than one (1) in every 140 minutes results in the component being configured in a fail-safe state with respect to its output blocks. Similarly, in an SIL-2 application, a threshold of one (1) error in every fourteen (14) minutes results in configuring the component infail-safe state. Last, for SIL-1 applications, the error threshold is desirably one (1) every 1.4 minutes. Other error rates may be utilized for other safety implementations, as desired. Commonly, authenticator error detection is not need if the replicated data method described herein is used.
Diagnostics Transducer Block
• One or more diagnostic transducer blocks can be used in a function block fieldbus Architecture or similar architecture. However, commonly only one diagnostic transducer block exists per SIS device. The diagnostic transducer block generally includes a timer and set of counter tracks which monitor all communications to/from the device (i.e., VCRs) for errors. Counters may include those for: bad authenticators, the time at which the last bad authenticator was received, the number of bad sequence numbers, the time at which the last bad sequence number was received, and the time since the last error was communicated through the black channel.
Black Channel Integrity Monitor
• A black channel integrity monitor can also be utilized. This monitor verifies that the rate of undetected errors (i.e., errors which are not detected by black channel monitoring devices but are detected due to bad sequence numbers or invalid authenticators) from the black channel does not exceed a given limit (either predetermine or set real-time). If the number of errors exceed the threshold, desirably, this monitor terminates black channel connections on which the errors are arising. Desirably, such connections are reinitiated upon operator intervention, reconnects and restarts. Automated or semi-automated reconnects and restarts can also be accomplished.
• Further, the extended actual protocol data unit implementation discussed above with reference toFIGS. 16D-16F and17D-17F can be utilized with or without the black channel integrity monitor.
Queuing Delay Monitoring and Detection
• Sequence number monitoring can also be accomplished. For example, in a publisher-subscriber connection, a message can be published with each macro-cycle. To aid in the detection of the queuing delays, at the start of the publisher-subscriber connection, the publisher communicates a sequence number to the subscriber for the connection. Then the subscriber increments the sequence number locally with each macro-cycle and compares it to the received sequence number, if the difference exceeds the max tolerable variance, then fail-safe or other appropriate actions may be triggered by the subscriber or otherwise.
Time Synchronization Monitoring and Detection
• Time synchronization across the black channel can also be accomplished. For example, the various embodiments can include a SIS Layer Time Synchronization Monitor (the “Time Monitor”). Such monitor desirably includes a crystal with at least 100 ppm accuracy and a resolution of at least 100 micro seconds. Other accuracies and resolutions, however, may be used in other embodiments.
• The Time Monitor executes after the black channel has processed a received time distribution PDU. The Time Monitor determines whether the drift between a black channel time and a SIS Layer's time is greater than a predetermined amount. In one embodiment, the allowable drift can be calculated as follows:
• 
  Allowable Drift=(TLCTD_n−TLCTD_n-1)*2*10⁻⁴
• where TLCTD_nis the time of the SIS Layer Clock after processing of the current Time Distribution (“TD”); and TLCTD_n-1is the time of the SIS Layer Clock after processing of the previous TD.
• Further, the actual drift can be calculates as follows:
• 
  Actual Drift=(TTD_n−TTD_n-1)−(TLCTD_n−TLCTD_n-1)
• where TTD_nis the Data Link Time (“DL-Time”) after processing of the current TD and TTD_n-1is the DL-Time after processing of the previous TD.
• Additionally, the Time Monitor sets a flag indicating excessive drift when the actual drift is greater than the allowable drift. Such flag can be set in a Resource Block's black channel sync error parameter. Likewise, if a valid TD is not received within a given time period, for example, within six (6) consecutive time distribution periods, the Resource block can also set the black channel sync error parameter. When the black channel sync error parameter is set, the Time Monitor will instruct the black channel to periodically send compel time (“CT”) sequences so as to resynchronize the time once every TD period. When the black channel sync error parameter is set and a fault occurs in a resource block, the data link layer is sent a reset so that both the fault and the time sync errors can be cleared simultaneously. Thus, it is to be appreciated that each SIS layer can include a Time Monitor that monitors whether resources are in sync and, if not, instructs the data link layers to take appropriate actions.
• As discussed hereinabove, the various embodiments provide for systems and processes for communicating data amongst SIS devices providing one or more SISC using a fieldbus Architecture and similar architectures and systems. While the present invention has been discussed with reference to certain architectures, functional blocks, processes, data structures and the like it is to be appreciated that the present invention is not so limited and is to be construed in accordance with the spirit and scope, as set forth hereinabove, and/or as presently claimed herein or claimed at a later time.

Claims (2)

1. An apparatus comprising:

a processor configured to determine whether at least one message communicated over a transmission medium has not been queued by monitoring time synchronization by comparing an actual drift to an allowable drift, wherein the allowable drift is calculated by comparing a first black channel clock determined after processing of a previous time distribution to a second safety layer clock determined after processing of a current time distribution and multiplying the result by a constant; and

a medium attachment unit, which communicates the time distributions and output messages between the processor and a transmission medium.

2-19. (canceled)

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