MONITORING SYSTEMThis invention relates to a monitoring and location system and more particularly but not exclusively to monitoring equipment to signal an alarm, or distress condition of one or more individuals enabling an individual to be located and subsequently rescued.
It is known to use equipment to signal when a person falls overboard from a waterborne vessel or an offshore platform. However, these existing equipments do not indicate the location or direction of the man overboard to the parent vessel or platform and there is a time delay in notifying rescue teams such as the Coastguard. In addition, if the missing person was lost from sight, or if lost overboard without anyone observing them, for example, at night or while on deck alone, there would be the added problem of how far the vessel had travelled since the person fell overboard resulting in a greatly increased area which requires to be searched.
More recently sophisticated monitoring systems have been marketed which bounce distress signals from a person or vessel in distress via a satellite to a rescue organisation. The signal enables the rescuers to compute the current position of the vessel in distress and to calculate its course until the transmitted signal is cancelled.
An aim of the present invention is to overcome the above mentioned disadvantages and provide an improved system which signals the presence or absence of a number of individuals or objects within a given distance of the monitoring equipment.
According to the invention there is provided a monitoring system comprising a receiver, one or more transmitters which incorporate an identity code and a preprogrammable microprocessor, wherein the microprocessor monitors the receiver which in turn monitors a signal of the/or each transmitter over a selected channel or over a discrete channel for each transmitter within a given period of time.
Preferably, the microprocessor detects either the presence or absence of a signal from the/or each transmitter and triggers an alarm or other signal.
Conveniently, the transmitter transmits an encoded signal, comprising a short burst of an encoded carrier wave and ceases transmitting for a pre-set period of time after which the cycle is repeated. Each transmitter is set to a different encoded signal and for a different quiescent period.
In the preferred construction, the monitoring system is constructed to receive predetermined coded signals from individual ones of the/or each transmitter in both a normal and an alarm condition.
Conveniently, the monitoring system is constructed to provide both audible and visual alarms as well as interfacing with associated equipment. One such item of associated equipment comprises a radio direction finding equipment.
Preferably, the microprocessor monitors the codes received by the receiver and times the duration between consecutive receipts of each coded signal. Should the time extend beyond a preprogrammed value, an alarm identiying the individual transmitter will be initiated.
An embodiment of the monitoring system, according to the invention will now be described by way of example only, with reference to the accompanying drawings in which:Figure 1 is a block diagram of a receiver and microprocessor system according to the invention;Figure 2 is a diagrammatic block diagram of a microprocessor for use with the system shown in Figure 1;and Figure 3 is a diagrammatic block diagram of an individual transmitter.
The monitoring system comprises a receiver for receiving signals via an aerial 1 to a monitor channel receiver e.g.
(205KHz) 2 for monitoring the frequency of the received signals which are transmitted to a monitor decoder 3 and passed to an input port 4a of a microprocessor 5.
Signals received by the aerial 1 are also passed to an alarm channel receiver e.g. (410KHz) 6 which monitors the alarm frequency, which signals are then transmitted to an alarm decoder 6a and passed to the input port 4k of the microprocessor.
The frequencies indicated above are given by way of example only and would be dependant on channel allocation by the D.T.I.
The microprocessor 5 includes an input port 7 for a set of controls 8 and two output ports 9 and 10 leading to an optional display 11 and alarm outputs 12 respectively.
The microprocessor and decoders are shown in more detail in Figure 2 and comprise a monitor channel decoders 13 for codes 1 to 15 and 16 to 31 leading to an 8 bit 2:1 multiplexer 14.
Second alarm channel decoders 15 for codes 1 to 15 and 16 to 31 leads to the multiplexer 14. The output of the multiplexer 14 leads to an input port 16 and to the microprocesor 5. Connected to the microprocessor are a programmable memory 17 and a variable memory 18. The program is stored in the programmable memory and defines the exact method of operation of the microprocessor. The program may be changed for different applications or for particular requirements of an application. The variable memory is used to store temporary values of variables associated with a program for an application. An 15 input port- 19 with a series of switches 20 is connected to the microprocessor.
Leading from the microprocessor 5 is an output port 23 which in turn leads to an alarm driver 24 illustrated as a relay. An output port 25 is also connected to the microprocessor 5 and is connected to the optional display 11.
The multiplexer 14 is connected via 26 to the output port 25.
The monitoring system may include between one and thirty one transmitters, one of which is illustrated in Figure 3.
The individual transmitter has a crystal oscillator 27 connected to a divide by nl network 28 which is connected to a modulator 31 by switch 30a in the normal mode of operation. The crystal oscillator is also connected to the quiescent period encoder 35 which is connected to the PPM encoder 36 by switch 30b in the normal mode of operation.
The PPM encoder is also connected to the modulator 31. The switches 37 and 38 preset the coding of the individual transmitter.
The output of the modulator is connected to a low power network 32 and by switch 30c to the output amplifier 39.
The output signal from 39 is then fed to an aerial 40.
Switches 30a, 30b and 30c are linked.
In the alarm mode of operation, switches 30a, 30b and 30c are moved to their alternative positions. The crystal osscillator is now connected to a divide by n2 a network 41 and thence to the modulator thus changing the transmitted frequency.
The crystal oscillator is also connected to an AlarmMessage' encoder 34 and thence to the PPM encoder thus providing a different message but with the same transmitter number encoding. The output of the modulator is connected to a high power network 33 and thence to the output amplifier 39 thus providing a higher signal level in the alarm state.
The microprocessor system monitors the codes received from all the transmitters and will time the duration between consecutive receipts of each code. If the time extends beyond a preprogrammed value, eg. 30 seconds, an alarm output will be initiated.
Because the predetermined gaps for each transmitter are different, no transmitter will continuously interfere with any other transmitter. By appropriate selection of the time gap variations for each transmitter, the maximum time required to receive a clear transmission from any transmitter can be limited to a reasonable time for this application.
The fail safe system of the present invention monitors the presence or absence of a signal from individuals or objects carrying a transmitter within a given distance via a single transmission channel. The system also incorporates manual and/or automatic means for signalling an alarm or distress condition of an individual to the receiver. While the distress signal is activated, radio direction finding equipment may be used to locate the individual or object being monitored.
Each transmitter sends a predetermined code consisting of a short burst of a digitally encoded carrier wave after which it shuts down for a pre-set period. Individual transmitters are set to different codes and for different quiescent periods. The choice of a suitable range of quiescent periods, enables all transmitters to be correctly received over a single channel within a given period of time. If the transmitter is switched either automatically or manually to the distress state, then the transmitter changes its transmission channel, and increases its rate and power of transmission to incorporate an alarm message which also contains its identity (P.P.M.)The receiver monitoring equipment. has means to provide both audible and visual alarms as well as the capability of interfacing with other equipment.The most suitable transmission medium for this application would be by radio, with the transmitter power in milliwatts giving a range of approximately 100 metres during normal operation, increasing to approximately 1 kilometre in the alarm/distress condition.
The transmitters may be fitted with a manual and/or automatic water activated alarm/distress switch, a visual indicator of operation and a rechargeable battery as a power source.
The receiver is configured to monitor the transmitters carried by personnel on board the vessel or on the offshore platform or other locations. In the event of the receiver failing to detect the signal from an individual transmittereither because the transmitter has failed or because it has moved out of range, e.g. ' when a person has fallen overboard, an alarm will be issued.
Alternatively, should the manual or automatic switch be operated, then the receiver will again raise an alarm.
Should the receiver detect an alarm from a transmitter, it will display the number assigned to that transmitter, it is possible that the alarm state of a transmitter not assigned to the particular receiver, eg. from another vessel may be detected. In this event, the receiver will issue an alarm and identify this as an alternative source, thus allowing the vessel to render assistance as required under maritime law.
When setting up the monitoring unit it will display each transmitter it is monitoring for absence of a signal as that transmitter is selected.
On receipt of an alarm condition, or detection of loss of signal from a transmitter, the monitoring unit will issue an alarm as follows:(i) Display the number of the transmitter;(ii) Indicate whether the alarm is a distress signalor loss of signal;(iii) Operate an internal audible buzzer;(iv) Operate an output to drive a Klaxon or otherdevice;(v) Operate other outputs to initiate actions onany other equipment interfaced to this unit(e.g. a Decca Navigator).
The 'mecca Navigator' has the facility to store its current position and to display the course and distance back to a previous location, until this function is cancelled.
This is known as the man overboard function.
The monitoring system according to the invention monitors all crew members within a given area around the receiver.
This may be achieved using several different methods all using radio emission.
1. Pulse code modulation (PCM) in which a carrier wave is transmitted in- very short bursts to form a code.
This code can then be received and monitored.
2. Frequency monitoring where the absence of amonitored frequency causes alarm to be raised.
3. By a master station transmitting an interrogationpulse (coded or not) to which each transmitterresponds in turn, the absence of a reply causes analarm to be issued.
4. Encoding of identifing signals into thecarrier wave from the transmitters could beby any one of the following:1. Digitaly [PPM or PCM or both]2. Analog by [Selective tone, Multitone,phase, frequency or amplitude modulation.
For illustrative purposes only Digital iePPM has been used in the system describedherein.
To limit the detection of what are termed normal signals to the area of the vessel or platform or other location and to reduce the distance that the 'person overboard' must be from the vessel before the alarm is raised the signal strength must of necessity be low. In addition, by transmitting in short bursts, the battery life of the transmitters is extended.
The quiescent time between transmission bursts should be of different lengths for each individual transmitter, the difference in length of quiescent time prevent two or more transmitters transmitting together each time they transmit and thereby continuously interfering with each others signals. However, this is not necessary where multiple frequencies are used. These methods all provide protection against failure of a transmitter or transmitters.
In another application of the monitoring system, according to the invention, means are provided to locate a person or object by radio direction finding. This radio location method requires changes to the transmitters to overcome the following inherent parameters of the above system, when an alarm is raised.
1. Interference from other transmitters monitored bythe vessel or platform receiver.
2. The transmitter is out of detection range.
3. The duration of the quiescent period is too long foreasy direction finding.
These inherent problems are overcome by causing a substantial increase in transmitted signal power, pulse repetition rate and a change in transmitter frequency, which can be 5 initiated as follows:1. Manually operated switch.
2. Water/pressure activated switch (automatic).
3. Temperature activated (sudden cooling on immersionautomatic).
4. Failure to receiver interrogation pulse from thevessel or platform receiver.
An additional benefit of the monitoring system of the present invention is that location of the 'person or object overboard' is not limited to the transmitter being preprogrammed into the monitoring unit, i.e. any vessel fitted with the monitoring unit will be alerted and able to obtain a location bearing on the transmitter which has triggered its alarm, whilst still monitoring its own transmitters.
Although the invention has been described with reference to a monitoring system for individuals on waterborne vessels and offsore platform or other locations, various modifications can be made to the invention, for example, the transmitters can be fitted to objects or to personnel moving in a secure environment, so that the presence or absence of these transmitters and thereby the persons or objects can be monitored.
A specific application would be to incorporate a transmtter into a Dan buoy which could in turn be attached e.g. to a life buoy or raft, because of the nature and construction of the Dan Buoy this would give considerably increased range.
The Dan buoy could when used with a suitable radio direction finding receiver be considered to be a stand alone device. However, its PPM encoding would initiate an alarm state in any monitoring system within range.