GB2349971A

GB2349971A - Intruder detection system

Info

Publication number: GB2349971A
Application number: GB9912208A
Authority: GB
Inventors: Craig Leivers; Peter Lancaster Bell; Richard Gary Wood
Original assignee: Pyronix Ltd
Current assignee: Pyronix Ltd
Priority date: 1999-05-10
Filing date: 1999-05-10
Publication date: 2000-11-15
Anticipated expiration: 2019-05-10
Also published as: GB2349971B; GB9912208D0

Abstract

To obtain NACOSS approval, an intruder detection system must pass various stringent tests. For example, the voltage and current of the signal generated by an intruder detection device must fall within specific criteria so as to be interpreted correctly by an interface panel. The use of conventional relays interferes with the correct operational voltages and currents, which can lead to a failure to obtain NACOSS approval and may also lead to an incorrect interpretation of the signals by the interface panel. Accordingly, the present invention provides an intruder detection system comprising an intruder detection device 104, at least one interface panel 102 for controlling the operation of the intruder detection and for monitoring receiving signals from the intruder detection device and at least one relay board 112 (Fig.2) comprising means operable in response to the signals from the intruder detection device to produce at least one output signal via a relay without interfering with the signals between the intruder detection device and the interface panel. As described, the relay board comprises a differential amplifier (206) having a very high input impedance, a rectifier (212), a comparator (214) and a relay (216).

Description

2349971 RELAY BOARD The present invention relates to a relay board and

more particularly to such a board suitable for use in an intruder 5 detection/security system.

Intruder detection systems typically comprise a central interface panel coupled to a number of microwave/ inf ra -red detectors, that is, combined technology detection devices, a number of output devices, such as audio/visual devices. and at least one keypad. Each detector is located so as to cover a protected space. The signal generated by a detector is transmitted to the central interface panel, which interprets the signal and takes appropriate action, for example, producing an audible alarm. It will be appreciated that the signal is carried typically by two wires connecting to the interface panel.

often, an intruder detection system will comprise, in addition to the interface panel, a further panel, conventionally known as a mimic panel, that mimics central interface panel or at least shows the states of various detection devices constituting the system. These further panels conventionally take as inputs, signals derived from the detection devices. Wires leading to the further panel are connected in parallel with the wires that connect the detection device to the central interface panel. A relay is often used to realise such a connection of the detection device to the further panel. The relay is actuated by a change in the state of the signal being output from the intruder detection device.

To obtain NACOSS or other Police approved inspectorate approval an intruder detection system must pass various stringent tests in accordance with BS4737. For example, the voltage and current of the signals used by the panels and 2 intruder detection devices must fall within specific criteria. It has been found that the use of conventional relays interferes with the correct operational levels of such voltages and currents, which can lead to a failure to obtain NACOSS approval. Furthermore, any such interference may also lead to an increase risk of false alarm, which is clearly undesirable.

It is an object of the present invention to at least mitigate some of the problems of the prior art.

Accordingly, a first aspect of the present invention provides an intruder detection system comprising an intruder detection device, at least one interface panel for controlling is the operation of the intruder detection system including monitoring signals derived from the intruder detection device and at least one relay board comprising means operable in response to the signals from the intruder detection device to produce at least one output signal via a relay without interfering with the signals between the intruder detection device and the interface panel.

Preferably, an embodiment of the present invention provides an intruder detection system in which the relay board comprises an input stage for receiving the signals, the input stage being arranged to draw sufficient current for correct operation of the relay board without adversely affecting the operation of the intruder detection system, that is, the relay does not draw that much current as to cause the intruder detection system to fail the NACOSS approval procedure and/or does not cause the interface panel to misinterpret the signals derived from the intruder detection device.

It can be appreciated that the present invention allows the detection of an alarm condition and allows the alarm condition to be reflected on, for example, a mimic panel, or 3 allows the alarm signal to actuate, via the relay board, some other device.

Advantageously, due to the very high input impedance of the relay board, the voltage and current signals generated by the intruder detection devices are not adversely affected by the presence of the relay thereby improving the prospect of a successful NACOSS approval and reducing the risk of incorrect operation of the intruder detection system.

A second aspect of the present invention provides a relay board for an intruder detection system, the relay board comprising means operable in response to input signals derived from an intruder detection device to produce at least one output signal via a relay without interfering with the input signals.

Preferably, an embodiment provides a relay board in which the relay board comprises an input stage for receiving the signals, the input stage being arranged to draw sufficient current for correct operation of the relay board without adversely affecting the correct functioning of the intruder detection system.

Furthermore, it is often the case that the mimic panel comprises a respective power supply that is distinct from the power supply of the main interface panel.

Advantageously, the relay board according to the present invention does not adversely affect the proper functioning of the alarm system.

Accordingly, a further aspect of the present invention provides a relay board comprising means for compensating for differences between the voltage levels of the power supplies of the interface panel and the relay board.

4 Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

figure 1 shows schematically an intruder detection system; and f igure 2 illustrates a circuit diagram of a relay board according to an embodiment of the present invention Referring to figure I there is shown an intruder detection system 100 comprising an central interface panel 102, a plurality of intruder detection devices 104 and, for example, a mimic panel 110. Such an intruder detection system is available from Pyronix Limited under the trade name X, model number Y. The interface panel comprises a display 106 which reflects the status of the system, that is, it shows which alarms are activate or inactive and which havebeen tripped. The interface panel also comprises a keypad 108 for controlling or setting the alarm system. The interface panel 102 allows a user to control the alarm system 100 by changing various settings. Changing various settings is well known within the art and may relate to, for example, activating or deactivating selected intruder detection devices 104, that is, determining whether or not the interface panel will respond to a change in the signals from the selected intruder detection devices 104. The intruder detection devices 104 may be combined technology event detection devices that use two or more technologies, such as, for example, microwaves and infrared technologies, in determining whether or not an intruder has been detected within a protected volume. The interface panel 102 is operable to detect a change in state of a signal received or derived from an intruder detection device 104. The mimic panel 110 can be arranged to reflect, for example, information displayed on the main interface panel 102. Typically, a mimic panel has independent connections to the various intruder detection devices 104. The wires to the mimic panel are connected to relays 112 that are actuated in response to the presence, absence and/or a change in the signals output from the intruder detection devices.

Referring to figure 2, there is shown a circuit diagram of a relay board 200 according to an embodiment of the present invention. The relay board is used in place of the conventional relay 112 described above in relation to figure 1. The inputs 202 and 204 to the relay board receive signals from the wires that connect an intruder detection device to the central or main interface panel. A differential amplifier 206 provides a very high input impedance for the relay board.

The very high input impedance allows the relay board to be connected to the wires of the intruder detection device without, or at least mitigating, the risk of interfering with the correct operation of the alarm system and, in particular, does not interfere with the correct interaction between the intruder detection device and the interface panel.

The differential amplifier 206 is arranged is have a non zero output, that is, Voffsetl in response to no difference between the input signals. The offset is achieved using a reference circuit 208. The reference circuit comprises a configurable potential divider having four resistors R3 to R6 and three connection or jumper pins 210. The resistors used to form the potential divider are selected by appropriate coupling between the connection pins 210. For example, providing no connection between the pins results in the parallel combination of resistors R3 and R6 in series with resistor R5. In contrast, shorting connections pins 1 and 3 merely provides the parallel combination of R3 and R6.

Further, providing a header between pins 1 and 2 results in the combination parallel combinations of resistors R3 and R6 in series with the parallel combination of resistors R4 and R5. It will be appreciated that a further resistance could be used to bridge the pins rather than a using a mere short.

6 This leads to a increased flexibility in configuring the reference circuit.

Any relay board having a respective power supply that it added to the intruder detection system will that power supply referenced to the same earth or Ov as that of the power supply for the intruder detection system.

It will be appreciated that the use of the offset allows the relay board to functional correctly notwithstanding the inputs to the relay board being connected in the opposite sense, that is, being reversed, and notwithstanding the power supply used for the main interface panel and intruder detection devices being different to the power supply of the relay board, in the sense of having slightly different output levels.

The output of the differential amplifier 206 is coupled to a fullwave rectifier 212 that is arranged to produce a rectified version of the output of the differential amplifier, in effect, the offset, Voffset, is removed leaving a rectified version of the signals derived from the intruder detection device. The output of the rectifier is a signal having a positive voltage.

Preferably, the output of the rectifier is compared to a reference voltage derived the reference circuit 208 using a comparator 214. The comparator 214 is arranged via the positive feedback resistor R12 to have a some hysteresis.

Typically, a 45 mV hysteresis is provided.

The relay board further comprises a relay 216 that is actuable in response to a change in the signals input to the relay board. The relay 216 preferably uses a LS4148 diode available from, for example, RS Components, across the inputs to the relay 216. The outputs of the relay 216 are NC1,C1, 7 NO1 and NC2, C2 and N02 which represent. It will be appreciated that if the relay board is connected to a zone in its quiescent, none-active state, the NC (normally closed) terminals are connected to the C (common) terminals and the normally open (NO) terminals are left floating. As a zone changes into an alarm state, the C terminal connects to the NO terminal leaving the NC terminal floating. Both sets of contacts operate in an identical manner. Two sets of contacts are provided for cases in which the relay board is required to provide two independent circuits. The relay is latched in response to the output of the comparator. When the output of the comparator is high, the relay is switched on, when the output of the comparator is low, the relay is switched off.

is Optionally, an embodiment provides a programmable timer 218 that is used to control the period of time for which the relay is, for example, switched on. The timer is provided with header pins 220 that are used, in effect, to bring into operation or bypass the timer. When a header is not used, the pins are open circuit and the action of the relay closely follows the signal output from the comparator. When the header is in place, the capacitor C7 is charged. The charged capacitor slowly discharges via resistors R21 and R24 and transistor Q2. The RC time constant of the series combination of R21 and R24 and the value of the capacitor determines the duration of the discharge and in turn the time period for which the relay is latched on. The RC time constant is adjusted using the variable resistor R24. An LED 222 is used to provide an indication of the status of the relay.

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Claims

1. An intruder detection system comprising an intruder detection device, at least one interface panel for controlling the operation of the intruder detection system including monitoring signals derived from the intruder detection device and at least one relay board comprising means operable in response to the signals from the intruder detection device to produce at least one output signal via a relay without interfering with the signals between the intruder detection device and the interface panel is

2. An intruder detection system as claimed in claim 1 in which the relay board comprises an input stage for receiving the signals, the input stage being arranged to draw sufficient current for correct operation of the relay board.

3. An intruder detection system as claimed in claim 2 in which the input stage comprises a differential amplifier arranged to produce an output derived from the signals.

4. An intruder detection system as claimed in claim 3 in which the input stage has an input impedance greater than 1MQ and is, preferably, at least substantially 2MM

5. An intruder detection system as claimed in either of claims 3 and 4 in which differential amplifier is arranged to be operable with signals of any polarity.

6. An intruder detection system as claimed in any of claims 3 to 5 in which relay board and the intruder detection device comprise respective power supplies and the differential amplifier is arranged to be operable 9 notwithstanding differences in the supply voltages of the power supply.

7. An intruder detection system as claimed in any of claims 3 to 6 further comprising a first reference circuit for supplying a reference voltage to the differential amplifier.

8. An intruder detection system as claimed in any preceding claim wherein the relay is actuable in response detection of the signals.

9. An intruder detection system as claimed in any preceding claim in which the relay is actuable in response to a change in the signals.

10. An intruder detection system as claimed in any preceding claim further comprising rectifier for rectifying the output of input stage to produce a rectified signal.

11. An intruder detection system as claimed in any preceding claim further comprising a comparator arranged to produce an output signal related to the rectifier output signal and an offset signal.

12. An intruder detection system as claimed in claim 11 in which the offset signal is derived from a second reference circuit using the power supply of the relay board.

13. An intruder detection system as claimed in claim 12 in which the first and second reference circuits form part of a programmable reference circuit such that the resistance of the first and second reference circuits can be changed.

14. An intruder detection system as claimed in any preceding claim further comprising hysteresis means for introducing a hysteresis between the on/off states of the relay.

15. An intruder detection system as claimed in claim 14 in which the hysteresis means is arranged maintain a state of the relay for a predeterminable period of time.

16. An intruder detection system substantially as described herein with reference to and/or as illustrated in the accompanying drawings.

17. A relay board for an intruder detection system, the relay board comprising means operable in response to the input signals to produce at least one output signal via a relay without interfering with the input signals.

18. A relay board as claimed in claim 17 in which the relay board comprises an input stage for receiving the signals, the input stage being arranged to draw sufficient current for correct operation of the relay board.

19. A relay board as claimed in claim 18 in which the input stage comprises a differential amplifier arranged to produce an output derived from the signals.

20. A relay board as claimed in claim 16 in which the input stage has an input impedance greater than 1MK2 and is, preferably, at least substantially 2MO.

21. A relay board as claimed in either of claims 19 and 20 in which differential amplifier is arranged to be operable with signals of any polarity.

22. A relay board as claimed in any of claims 19 to 21 in which relay board and the intruder detection device 11 comprise respective power supplies and the differential amplifier is arranged to be operable notwithstanding differences in the supply voltages of the power supply.

23. A relay board as claimed in any of claims 19 to 22 further comprising a first reference circuit for supplying a reference voltage to the differential amplifier.

24. A relay board as claimed in any of claims 17 to 23 in which relay is actuable in response detection of the signals.

25. A relay board as claimed in any of claims 17 to 24 in which the relay is actuable in response to a change in the signals.

26. A relay board as claimed in any of claims 17 to 25 further comprising rectifier for rectifying the output of input stage to produce a rectified signal.

27. A relay board as claimed in any of claims 17 to 26 further comprising a comparator arranged to produce an output signal related to the rectifier output signal and an offset signal.

28. A relay board as claimed in claim 27 in which the offset signal is derived from a second reference circuit using the power supply of the relay board.

29. A relay board as claimed in claim 28 in which the f irst and second reference circuits form part of a programmable reference circuit such that the resistance of the first and second reference circuits can be changed.

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30. A relay board as claimed in any of claims 17 to 29 further comprising hysteresis means for introducing a hysteresis between the on/off states of the relay.

31. A relay board claimed in claim 30 in which the hysteresis means is arranged maintain a state of the relay f or a predeterminable period of time.

32. A relay board substantially as described herein with reference to and/or as illustrated in the accompanying drawings.