GB2226418A

GB2226418A - Testing alarm circuits

Info

Publication number: GB2226418A
Application number: GB8926669A
Authority: GB
Inventors: John Corkan
Original assignee: Argos Alarms & Security Produc
Current assignee: Argos Alarms & Security Produc
Priority date: 1986-04-24
Filing date: 1989-11-24
Publication date: 1990-06-27
Anticipated expiration: 2006-04-24
Also published as: GB8609969D0; GB2189613A; GB2189613B; GB8926669D0; GB2226418B

Abstract

A monitoring means comprises a pulse generator (7) which sends pulses through a sensor (1) and a wiring loop (2) of an alarm system. A pulse detector (9) senses any interruption in the regular flow of pulses if a fault exists and then activates a warning unit (12). A plurality of detectors (9), each reacting to an interruption of a different length of time, may be selectively engaged (8) to diagnose the fault. <IMAGE>

Description

MONITORING XSANS FOR TESTING Rt-sCTBICAIt ELECTRONIC CIRCUITRY OR COMPONENTS We, Argos Alarms and Security Products Ltd., a British Company of 10 Baldwin Street, Hawcoat, Barrow-in- Furness, Cumbria, IA14 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 loan of credibility caused by 'false alarms', there is a further problem. When an alarm on a shop or business sounds, say at night, then 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 the Manager/Proprietor, who will have to go to the premises with thi utmost haste.

Should the alarm have been -a-false one, both Police and Msnager/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 one method of checking the wiring, 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 zer- 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 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 monit oring means; ii) a source of electrical power; iii) a pulse generator capable of generating a series of regularly timed pulses of electricity; iv) a pulse detector capable of detecting said series of regularly timed pulses of electricity and having the capacity to produce an output signal should the series of regularly timed pulses of electricity be interrupted;; v) a warning means capable of- reacting to said output signal to alert the person using said monitoring means.

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 figure which is a block diagram of the electrical/ electronic circuit monitoring means.

Alarm systems usually consist of s 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. A further purpose is, in the case of intermittent faults, to ascertain the approx sate duration for which the fault persists and thereby provide diagnostic evidence to help to identify the fault.

Referring to the Figure, a sensor I 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 alma a system control unit (rot shown), it may be necessary to disconnect wiring 2 aroz the terminals 3, before monitoring tne 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 cottenced. Sensor 1 may be one of two types. It will either open or close wrien the alarm condition is detected. This psrt 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.

A pulse generator 7 sends a regular stream of electrical pulses via wiring 2 and sensor 1 to a selector switch 8, and thence to one of a plurality of pulse detectors 9. As the pulses from generator 7 are even in magnitude and produced regularly - say I 000 per second - it is known how to produce a s detector to react to the presence, or absence of such pulses. The detectors 9, of which four are shown in this example, are designed.to react only to the absence of a pulse or pulses. To test wiring 2 and sensor I for the presence of a fault, the operator will leave the monitoring means circulating regular pulses of electricity around the circuit shown in the figure. He/she will then proceed to "manipulate" every part of the whole length of wiring run 2.

I- an internittent break is discovered, the regular flow of pulses will be interrupted, causing that one of detectors 9 which is it the circuit to react to the absence of regular pulse$) and produce an output signal in one of wires 10 activating warning unit 12.

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 I 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 huzzer 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.

Where there were no breaks in the wiring 2; pulse detector(s) 9 would not react and the pulses would travel via one connection 13 back to power source 14 (or 16).

Four pulse detectors 9 are shown in the figure.

Each would react to a different number of 'missing' pulses.

For example, in the caae of a pulse generator 7 producing 1 000 pulses per second, i.e. one pulse per millisecond (ms), one detector 9 could register an alarm if only one pulse was missing-, i.e. a break in electrical continuity of only I ms.

Another detector 9 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 8 would be set to the detector 9 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 9 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 9.

A timer 11 may advantageously be incorporated between the detector 9 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 11. Firstly, it would save power - particularly useful if power source 14 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. The power source 14 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 15 , powered from the mains 16 would be better.

The optimum would be rechargeable cells with a built-in mains charger 15 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 16; at the same time the cells 14 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 14 could supply the powder. 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 14 to be~~displayed on a meter.

The description so far has been written for the testing of s-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 fA. Similarly, sensor 1 could be checked by itself if jump leads 4 were connected to terminals IA instead of to terminals 3.

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.

In this case, the sensor I would be shorted out of the circuit by connecting a jump lead across terminalsiA. The wiring 2 would then be tested as previously described.

Sensor I would be tested separately.

Claims

'::hat we claim is:

1) Apparatus for monitoring the integrity of electrical/electronic circuits or compnn^ts thereof comprising: a means for electrically connecting the monitoring means to the circuit, or parts of that circuit, to be tested; a source of electrical power; a pulse generator; a pulse detector, capable of producing an output signal if the regular flow of pulses is interrupted; a warning means, capable of redacting to the output signal from said pulse detector.

2) Apparatus for monitoring the integrity of electrical/ electronic circuits, as claimed in claim 1, in which a plurality of pulse detectors may be used selectively, each of said plurality of pulse detectors capable of producing an output signal only if the regular flow of pulses has been interrupted for more than a specific period of time.

3) ApparatuS for monitoring the integrity of electrical/ electronic circuits as claimed in claim 2 wherein the warning means may be one, or more of, a light, an audible device and/or a transmitter communicating with a receiver carried by the operator.

4) Apparatus for monitoring the integrity of electrical/ electronic circuits as claimed in claim 3 wherein a timing device is used simultaneously to switch off the warning means after a predetermined period.

5) Apparatus for monitoring the integrity of electrical/ electronic circuits as claimed in claim 4 wherein the power source may be batteries or rechargeable cells.

6) Apparatus for monitoring the integrity of electri.sl/electronic circuits as claimed in claim 4 wherein the power source may be mains electricity.

7) Apparatus for monitoring the integrity of electrical/electronic circuits as claimed in claims 5 or 6 wherein the power source may be either mains electricity or.rechargeable cells, with said rechargeable cells being rechargeable by said mains electricity when said mains electricity is being used as the power source.

8) A method of monitoring sensor circuits, and parts thereof, wherein a continuous flow of regular pulses are caused to flow through said sensor circuit and subsequently be detected by a pulse detector such that if, while said sensor circuit is being examined, the flow of pulses is interrupted, said pulse detector will cause a warning to be registered.

9) A method of monitoring sensor circuits, or parts thereof, as claimed in claim~8, wherein a series of pulse detectors, each capable of responding to an interruption in the flow of pulses lasting for more than a specific period of time, may be used to provide a diagnostic indication of the type of fault present in said sensor circuit.

Referenced C omoonents 1. Sensor IA. Terminals 2. Electrically conducting wires 3. Terminals on alarm system 4. Jump leads 5. Terminal on monitoring means 6. Terminal on monitoring means 7. Pulse Generator 8. Multiposition Switch 9. Pulse Detectors

10. Connections

II. Timer

12. Warning Unit

1 3. Connections

14. Bsttety/rechargesble cells

15. Battery charger and/or transformer and rectifier

16. Mains Electricity