GB2218244A - Security system control panel - Google Patents

Abstract

The control panel 10 is for connection to a plurality of sensors 12 which may be for example, infra-red detectors, reed switches, a microwave fence system etc. Normal alarm means 16 is actuated by comparison of output signals from the sensors with a reference value stored in a first comparator 14. Switching means 18 is included to permit the normal alarm means 16 to be turned off during periods when the alarm would be actuated by authorised personnel encroaching on the sensors' 12 field of operation. During such periods alarm signals are either counted by counter 20 or their pattern is monitored and compared with a predetermined value or pattern stored in comparator 22. If the counted number is less than the predetermined value, which is preferably equal to the minimum number of alarm signals which should be caused by the authorised personnel, then second alarm means 24 is actuated. <IMAGE>

Description

SECURITY SYSTEM CONTROL PANEL This invention concerns a control panel for monitoring a security system comprising a pluraltiy of intruder detection sensors.

Security systems for use in the protection of, for example, a building or a group of buildings, generally comprise a large number of sensing devices which may be for example, microwave generators and receivers, passive or active infra-red devices, infrasonic or ultrasonic sound detectors, reed switches on windows or doors, etc.

Each of the individual sensing devices is connected to at least one central control panel where each device's status is monitored. If one or more of the sensors is activated by, for example, the presence of an intruder within its sensing field, a signal is generated which will cause an alarm to be activated on the respective central control panel thus bringing the intrusion to the attention of the system's operator or user.

During periods of time designated as 'safe' periods it is common to disable or otherwise turn off the control panel, at least in respect of a partial group consisting of one or more predetermined sensing devices, for a short period of time so that signals generated by the authorised presence of personnel, for example, maintenance or security personnel, does not produce an alarm on the control panel. During these 'safe' periods it would be possible for the sensing devices so affected to be permanently or temporarily de-activated or their sensing field restricted, for example, by the placing of a permanent magnet near a reed switch to hold the switch in its open condition or the covering up of a passive infra-red sensor so that an infra-red signal generated by an intruder could not be detected.Sensors deactivated in such a way would still be operational, however, they would be unable to generate an alarm signal in response to an intrusion within their sensing field. With the control panel inactive alarm signals caused by such tampering with the sensor or sensors could not be noticed by the system operator. Further when the panel is once again activated the sensors would still seem to be operational and a check of the electric circuits would show them to be operational The absence of any alarm signals from the sensors would not be an event noticeable by the system operator.

t is an object of the present invention to provide a security system control panel such that the tampering or de-activation of one or more sensors forming part of the security system whilst the panel is switched off will give rise to an alarm condition when the panel is turned on again.

With this object in view the present invention provides a security system control panel adapted for connection to a security system comprising a plurality of sensors, the control panel having normal alarm means actuable by an alarm signal generated upon detection of an alarm condition by one or more of the sensors, characterised in that the control panel is provided with switching means operative to prevent the normal alarm means from being actuated and to divert alarm signals generated by the sensors to a comparator operative to count the number of alarm signals generated and compare this to a predetermined value and further operable to actuate second alarm means when the number of alarm signals fails to exceed the predetermined value within a predetermined time period.

It will be understood that during maintenance or similar operations when alarm signals will be generated by authorised personnel the alarm means on the control panel would be temporarily de-activated. The predetermined value stored in the comparator will be equal to the minimum expected number of alarm signals which will be caused by authorised personnel. If the expected number of alarm signals is not reached this would be indicative of one or more sensors having been tampered with or otherwise de-activated.

The second alarm means controlled by the comparator may be such as to give a warning to the system user when the control panel is returned to normal operation.

Alternatively the alarm means could instruct the operator to check those sensors or group of sensors whose alarm signals have not reached the predetermined number; require the panel to be re-set by an authorised senior operator before normal operation can be resumed; or can report the occurrence to a further control panel at a separate location.

Advantageously the predetermiend time period is the entire time that the normal alarm means is de-activated.

Preferably the comparator has the ability to monitor the level of alarm signals generated during a maintenance period, store said level as the predetermed value and activate the second alarm means if there is any change from that predetermined value in subsequent periods.

The invention will be described further, by way of example, with reference to the accompanying drawing, in which the single figure is a schematic simplified block diagram of a preferred embodiment of the invention.

A preferred embodiment of a security system control panel 10 is connected to a plurality of sensors 12.

These sensors may be of any convenient known type, for example, passive or active infra-red detectors, strategically positioned reed switches, a microwave fence system, ultrasonic or infrasonic sound detectors etc or a combination of known sensor types. For each sensor 12 an ouput signal is generated by an intrusion into the sensor's field of operation. The signal is supplied to a first comparator 14 which compares the received signal value with a predetermined value. If the received signal value exceeds from the predetermined value, indicative of the presence of an intruder, the first comparator 14 generates an alarm signal which is supplied to normal alarm means 16 alerting the system operator to the presence of an intruder.

As has been explained previously, during safe periods the presence of authorised personnel in proximity to the sensors 12 will result in a number of alarm signals being generated. During such a period of activity the normal alarm means 16 is commonly switched off or deactivated by switching means 18. The signals generated by the first comparator 14 during this period are supplied to a counter 20 which counts the number of alarm signals generated in a pre-determined time period and supplies this number to a second comparator 22. The second comparator 22 has a predetermined value stored in it and compares this to the number suppplied by the counter 20. If the counted number is less than the predetermined value the comparator 22 generates an alarm signal activating second alarm means 24 to alert the system operator to the possible de-activation of one or more of the system's sensors 12.

The second alarm means 24 can be in several forms.

For example, the alarm means 24 may be such that the system's user is warned of the incident when the panel 10 is returned to normal operation by operation of switching means 18 or the alarm means 24 may prevent the panel 10 from being returned to normal operation without a check of each sensor 12 in the system.

Alternatively the actuation of the second alarm 24 could be recorded in a log or transmitted to a monitoring panel at a remote location.

In a modified embodiment of the invention the comparator 22 could be provided with the facility to monitor the pattern of activity and the signals generated by the sensors 12 during the period when the normal alarm 16 is switched off. The sequence of alarm signals so monitored is stored in the comparator as the predetermined value. If the pattern or sequence of alarm signals in a subsequent period of time departs from that previously monitored then the alarm means 24 would be actuated. It will be appreciated that such relatively complex functions of the counter 20 and the comparator 22 could be fulfilled by appropriate microprocessor circuitry or by re-programming of such existing circuitry in an operational control panel.

It will be understood that the foregoing is illustrative and not restrictive of the scope of the invention and variations are possible. For example, the sensors can be of any suitable type such as those already mentioned or sound or vibration detectors, motion detectors etc. The control panel could have second alarm means 24 for each sensor in the system such that it is possible to identify the precise sensor which has been de-activated. The second alarm means 24 may share common components or parts with the first alarm means 16. However, it is preferable that the system user should be able to distinguish between the alarm signals generated by the first and second comparators 14, 22 respectively. Other variations may also be possible.

Claims (8)

1. A security system control panel adapted for connection to a security system comprising a plurality of sensors, the control panel having normal alarm means actuable by an alarm signal generated upon detection of an alarm condition by one or more of the sensors, characterised in that the control panel is provided with switching means operative to prevent the normal alarm means from being actuated and to divert alarm signals generated by the sensors to a comparator, operative to count the number of alarm signals generated and compare this to a predetermined value and further operative to actuate second alarm means when the number of alarm signals fails to exceeds the predetermined value within a predetermined time period.

2. A panel as claimed in claim 1 wherein the predetermined value stored in the comparator is equal to the minimum expected number of alarm signals which would be caused by authorised personnel during a predetermined time period.

3. A panel as claimed in claim 1 or claim 2 in which the predetermined time period is substantially the entire time period during alarm signals generated by the sensors are diverted to the comparator by the switching means.

4. A panel as claimed in claims 1, 2 or 3 in which the second alarm means controlled by the comparator is such as to give a warning to a system user or operator when the control panel is returned to normal operation by operation of the switching means.

5. A panel as claimed in claims 1, 2 or 3 in which the second alarm means instructs an operator to check those sensors whose alarm signals had not reached the value stored in the comparator.

6. A panel as claimed in any preceding claim in which actuation of the second alarm means requires the panel to be re-set by an authorised senior operator before normal operation can be resumed.

7. A panel as claimed in any preceding claim in which the comparator has the ability to monitor the level of alarm signals generated during a maintenance period, store said level as the predetermined value and activate the second alarm means if there is any change from that predetermined value in subsequent periods.

8. A security system control panel substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.