SPECIFICATIONMonitoring means for testing electrical/ electronic circuitry or componentsWe, Argos Alarms and Security Products Ltd., a British Company of 10 Baldwin Street,Hawcoat, Barrow-in-Furness, Cumbria, LA 14 4HP, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement:This invention relates to methods of testing alarm systems, such as burglar alarms, fire alarms and the like, to determine whether the system is operating correctly and if there are any actual or inherent faults present. The invention may also be used diagnostically to determine the cause of 'false alarms', i.e. instances when the alarm has been triggered, but the condition which should have caused the alarm to be activated, is absent.
When a 'false alarm' occurs, i.e. when the alarm is activated for no apparent reason, such as a burglar alarm sounding in the absence of a break-in or a fire alarm sounding in the absence of a fire etc., then the reliability of the alarm system will be questioned. If 'false alarms' are very rare occurrences, then each one is likely to be treated as a genuine emergency. If, however, 'false alarms' are frequent, then the alarm system will lose its credibility and the warnings will be treated less urgently, or even ignored altogether; in such cases, a genuine alarm could easily be missed with serious consequences resulting.
In addition to the loss of credibility caused by 'false alarms', there is a further problem.
When an alarm on a shop or business sounds, say at night, when few people are about, the matter is likely to be brought to the attention of the local Police. They will send an Officer to investigate and contact theManager/Proprietor, who will have to go to the premises with the utmost haste. Should the alarm have been a false one, both Police and Manager/Proprietor will have been troubled unnecessarily. The Manager/Proprietor will reset the alarm using his 'security key' and then return home.
One type of fault in alarms, which causes much anxiety, is the 'intermittent fault', where a condition exists which occasionally activates the alarm, (or renders it useless, depending on the circuitry). With such a fault, it is not unknown for an alarm to be checked by a service engineer one day, give a 'false alarm' that night, and yet still be found to be operating correctly the next day. One of the most common causes of this type of fault is a break in the wiring under the cable sheath allowing contact to be broken (or made) on an intermittent basis. The reasons for the contact being broken (or made) may be random, e.g. wind pressure on the structure to which the wire is attached, or regular, e.g. thermal expansion/ contraction due to when the central heating comes on/goes off.When 'intermittent faults' occur, there are two methods of curing the problem:i) Replace all the wiring, which is time consuming and expensive.
ii) Check the wiring manually.
In the second method, a small current is passed through each wiring loop at a time; this is done using a suitable multimeter where a needle will indicate the magnitude of current flowing. While one person watches the needle, another would manipulate the whole wiring run. If there was a break in the wiring, the needle would return to zero indicating an open circuit. Unfortunately, this is not a foolproof method of checking. Some breaks in the wiring can be so transient that the inertia in the movement of the needle or a moment's lapse of concentration by the observer may fail to detect the break.
According to a first-embodiment of the invention, there is provided an electrical circuit monitoring means for the purpose of checking the continuity of electric/electronic circuitry and/or component parts thereof, said monitoring means consisting of;i) means for electrically connecting said electric/electronic circuitry and/or component parts thereof to said monitoring means;ii) a source of electrical power;iii) a means of measuring an electrical property directly relevant to the electric/electronic circuitry and/or component parts thereof when said electric/electronic circuitry and/or component parts thereof are connected to said monitoring means;iv) a programmable memory, the value of which may be set in relation to the reading given by said means of measuring;;v) a comparator able to compare continuously said reading given by said means of measuring with said value stored in said programmable memory and producing an output signal only when said reading is equal to, or greater than, said value stored in said programmable memory;vi) a warning means capable of reacting to said output signal from said comparator and alerting the person using said monitoring means.
Preferably the means of measuring would be a digital voltmeter calibrated in ohms so that the property directly relevant to the electric/ electronic circuitry and/or component parts thereof would be 'electrical resistance'. Ideally the memory could be programmed by the use of a rheostat(s) on the monitoring means which the operator could adjust, and the value selected could be displayed on the voltmeter read out at the time of programming. The warning means could be either one, or more, of a light, an audible device, e.g. a buzzer, or a radio transmitter communicating with a bleeper carried by the operator. Preferably a timer is incorporated to cancel automatically the warning means after a predetermined time.
According to a second embodiment of the monitoring means;i) said comparator may be set to produce an output signal when the reading given by said means of measuring is equal to or less than said value stored in said programmable memory.
According to a third embodiment of the monitoring means, a pulse generator may be used to send a continuous series of regularly timed pulses via the electric/electronic circuitry and/or component parts thereof, to a pulse detector which is used to detect said regularly timed pulses, said pulse detector having the capacity to produce an output signal to activate a warning means should the regularly timed flow of pulses be interrupted.
Preferably, a series of pulse detectors could be used each having preset circuitry to detect interruption of the pulse flow lasting for different intervals of time. A multiposition switch would be used to select the appropriate pulse detector.
A specific embodiment of the invention will now be described by way of example, with reference to the accompanying drawings, in which:Figure 1 is a block diagram of the first and second embodiments of the electrical/electronic circuit monitoring means.
Figure 2 is a block diagram of the third embodiment of the electrical/electronic circuit monitoring means.
Alarm systems usually consist of a central unit which reacts to incoming signals from any one of a plurality of sensors. These sensors are usually remote from the central unit and each sensor communicates with the central unit via electrically conducting wires. The purpose of the monitoring means in this disclosure is to prove the integrity, or otherwise, of each and every circuit comprising a sensor and the electrically conducting wires through which it communicates with the central unit.
Referring to Fig. 1, a sensor 1 communicates via electrically conducting wires 2 to terminals 3 on the central unit of an alarm system (not shown). Jump leads 4 connect the terminals 3 on the alarm to terminals 5, 6 on the monitoring means. There is thus an electrically conducting circuit from terminal 5 via jump lead 4, terminal 3, wiring 2, sensor 1, wiring 2, terminal 3, jump lead 4 to terminal 6. Depending on the electrical/electronic nature of the alarm system control unit (not shown), it may be necessary to disconnect wiring 2 from the terminals 3, before monitoring the condition of the circuit comprising components 1 and 2.
When the sensor circuit 1, 2 is connected to the monitoring means, the checking for electrical continuity may be commenced.
Switch 7 would be moved to a first position, which would complete the circuit from terminal 6, via switch 7, measurement means 8, power source 9 to terminal 5. As the sensor circuit 1, 2 is also connected to terminals 5 and 6, current will flow from power source 9 via wiring 2 and sensor 1 to measuring means 8 where the resistance of sensor circuit 1, 2 would be measured and displayed.
Though in this description, the 'resistance' of sensor circuit 1, 2 is used as an example, it will be apparent to those skilled in the art that the current (I) or voltage drop (V) could equally well be used as the measured property. As resistance (R) is defined by Ohm'sLaw (V/I=R), measuring means 8 will actually measure the current flowing in the sensor circuit 1, 2; depending on the calibration and circuitry within measuring means 8, the reading could be displayed either as resistance (ohms), current (amps) or potential difference (volts).
Sensor 1 may be one of two types. It will either open or close when the alarm condition is detected. This part of the description will be written on the basis that sensor 1 is of the first type, i.e. it opens in the alarm condition and is thus normally closed, i.e. electrically conducting in its passive state. Such a sensor 1 could be the thin wires on the inside of a window in a burglar alarm.
When the resistance of sensor circuit 1, 2 has been determined by measurement means 8, its value will be noted. The operator will then move switch 7 to its second position which would connect presetting means 10 into the circuit. Presetting means 10 would contain electronic components, such as rheostats, etc., which could be varied to allow a particular reference value to be set in a memory 11. Presetting means 10 would be adjusted to give a reference value in memory 11 slightly different to that measured previously 8. For example, if the value measured 8 was, say, 80 ohms, then the value in memory 11 could be set slightly in excess of this figure, e.g. 81-88 ohms, depending on the sensitivity required.
The operator would then return switch 7 to its first position as shown and proceed to examine the whole of the wiring run 2 from terminals 3 to terminals 1A. This would involve a visual examination for damage and manipulation of the conductors to check for breaks. In the event that there was a break in the wiring 2, the resistance of wiring 2 would suddenly increase as that part of the conductor was manipulated. When this occurred, measuring means 8 would register a value much in excess of 81-88 ohms. The value registered by means 8 would be continuously compared by comparator 13 with the value 11 in the memory and if the value 8 equalled or exceeded the value 11, a signal would be sent via connection 15 to warning unit 12 to alert the operator to the presence of a fault.
In the case just described, the method of checking would prove the reliability (or otherwise) of both wiring 2 and sensor 1. Thus the wiring 2 and sensors 1 of each sensor circuit may be checked in turn, until all sensor circuits have been proved.
The nature of warning unit 12 may be either a light, e.g. continuous or flashing, an audible alarm, e.g. a buzzer, or a radio transmitter to activate a bleeper carried by the operator. To conserve battery power, a switch (not shown) would be used to select the appropriate means of warning. For example, if the operator was testing sensor 1 with the monitoring means at his side, a light may be a suitable warning 12. If, however, the monitoring means had to be placed behind him, the buzzer would be most appropriate. When checking wiring runs 2, which may extend a considerable distance from the central unit of the alarm, e.g. through several rooms, or outside the building, the radio transmitter would be the most suitable.
The description above has been written on the basis of sensors of the first type which are electrically conducting in the normal passive state. Circuits containing sensors of the second type which are open in the passive state, e.g. a pressure switch under a mat in a burglar alarm, have to be treated with a slightly different procedure.
If sensor 1 is normally open in its passive state, the reference value in memory 11 would be set to a high figure, e.g. 30 000 ohms, and comparator 13 set to react to values of resistance 8 lower than this figure.
The wiring 2 would then be manipulated and the sensor 1 checked in the same way as before for the presence of any intermittent short circuits. The monitoring means would be provided with switchabie options (not shown) in the circuitry of comparator 13 to allow it to react to values either higher or lower than that stored in memory 11.
When the reference value is set in memory 11, the value of 81-88 ohms was quoted in the description above for the closed-circuit type of sensor 1. When checking for intermittent open circuits, any value greater than the 80 ohms measured 8 could be used. However, if too low a reference value 11 was set, e.g. 81 ohms, minor variations in the resistance of wiring 2 caused when it was manipulated might result in warning unit 12 being activated when no fault existed. If, on the other hand, the value 11 was set to too high a figure, e.g. 1 000 ohms, it is possible that a potential failure could be missed.For example, if each wire 2 consisted of several strands and all but one strand was broken at one point, manipulation of the wire might separate the broken ends but still leave a circuit through the unbroken strand; this would cause the resistance 8 to rise to, say, 500 ohmsnot enough to activate warning unit 12 via comparator 13. In this example, the monitoring means would fail to detect the partial break. Depending on the sensitivity of the circuitry in the alarm system (not shown), such a partial break could activate the alarm on an 'intermittent' basis. In practice, the reference value 11 should be set to a value about 10% greater than that measured 8, i.e. to 88 ohms in this instance.
A timer 14 may advantageously be incorporated between the comparator 13 and warning unit 12. The purpose of this would be to switch off the warning unit 12 after a predetermined time interval, e.g. 5-10 seconds. There would be two advantages of a timer 14. Firstly, it would save power-parti- cularly useful if power source 9 was a battery.
Secondly, it would relieve the operator of the task of having to reset the monitoring means.
This could be particularly useful when trying to identify the exact point of an intermittent fault in a wiring run, especially if the operator was remote from the monitoring means and using the transmitter as the warning 12.
If required a timing means, not shown, may be used to determine the length of time for which intermittent faults last. For example, when the fault position has been located, the timing means could be set so that warning unit 12 would react only to interruptions lasting longer than, say, 100 ms (milli seconds). If no warning 12 occurred, the time interval could be reduced to 50 ms and so on, until warning unit 12 was activated.
The power-source 9 would be of a low voltage and able to maintain a small current for a long period. Conventional disposable batteries could be used, but rechargeable cells with a built-in charger 16, powered from the mains 17, would be better. The optimum would be rechargeable cells with a built-in mains charger 16 and a system which could transform and rectify mains power down to the voltage required. In such a case, the monitoring means could be plugged into the mains near the central unit of the alarm system (not shown) and use mains power 17; at the same time the cells 9 would be recharged. If it was then necessary to remove the monitoring means to a remote location to check a sensor 1, the rechargeable cells 9 could supply the power.
In a practical design, a warning light (not shown) would indicate when mains power was being used. A switch (not shown) would allow the state of the cells 9 to be displayed on measuring means 8.
The description so far has been written for the testing of a complete sensor circuit, i.e.
wiring 2 and sensor 1. It is equally possible to test only a part of a sensor circuit. For example, wiring 2 could be tested by itself if a jump lead (not shown) were used to short terminals 1A. Similarly, sensor 1 could be checked by itself if jump leads 4 were connected to terminals 1 A instead of to terminals 3.
Fig. 2 shows a variation of the monitoring means. Where components are the same as those used in Fig. 1 and described above, the same reference numerals have been used.
Components not hitherto described bear the prefix "2". e.g. 20, 21 etc.
Referring to Fig. 2, a pulse generator 20 sends a regular stream of pulses via wiring 2 and sensor 1 to a selector switch 21, and thence to one of a plurality of pulse detectors 22. As the pulses from generator 20 are even in magnitude and produced regularly-say 1000 per second-it is known how to produce a detector to react to the presence, or absence of such pulses. The detectors 22, of which four are shown in this example, are designed to react only to the absence of a pulse or pulses.Thus, when the monitoring means is being used, as described above, with the operator manipulating wiring 2 and an intermittent break in the wiring is discovered, the break in the circuit will cause the flow of pulses to cease momentarily; under these circumstances, an output signal will be generated in one of connections 24 which will pass via reset timer 14 and connection 15 to activate warning unit 12. Where there were no breaks in the wiring 2, pulse detector(s) 22 would not react and the pulses would travel via one connection 23 back to power source 9 (or 16).
Four pulse detectors 22 are shown in the example in Fig. 2. Each would react to a different number of 'missing' pulses. For example, in the case of a pulse generator 20 producing 1 000 pulses per second, i.e. one pulse per millisecond (ms), one detector 22 could register an alarm if only one pulse was missing, i.e. a break in electrical continuity of only 1 ms. Another detector 22 could react only if 100 pulses were missing, i.e. a break of 100 ms. The other detectors could react to, say, 200 and 500 missing pulses. Such a feature would be a useful diagnostic tool as, to a skilled operator, the duration of the intermittent break could indicate which component was likely to be faulty.
In practice, selector switch 21 would be set to the detector 22 with the shortest time interval, e.g. 1 ms until an intermittent fault was found.
Then, having located the fault, the test would be repeated using detectors 22 with longer response times, until the fault could no longer be detected, i.e. the fault existed for a shorter time than the response time of that particular detector 22.
The skilled man should have no difficulty constructing a monitoring means according to the above disclosure. However, the following components from "Farnell Electronic Components" (October 1985 Catalogue) could form the basis of a monitoring means:Alarm Control P.C.B. (Ref. No. P41 144100) could form the basis of the Comparator13 and memory 11. Digital Panel Meter (Ref.
No. Q7 175-809) could be used as the display for measuring means 8.