GB2460138A

GB2460138A - Discriminating genuine and erroneous sensor signals using two sensors and two counters

Info

Publication number: GB2460138A
Application number: GB0904186A
Authority: GB
Inventors: Patrick Mccarthy; Clive Tripp
Original assignee: Bristol Water PLC
Current assignee: Bristol Water PLC
Priority date: 2008-03-06
Filing date: 2009-03-06
Publication date: 2009-11-25
Anticipated expiration: 2029-03-06
Also published as: GB0904186D0; GB2460138B; GB0804214D0

Abstract

A discriminator circuit 10 receives signals from first and second sensors 2, 4. The circuit 10 comprises a first counter 102, which is operable to increment a first count value upon reception of output from the first sensor 2, and to decrement the first count value upon reception of output from the second sensor 4. The circuit 10 also comprises a second counter 104, which is operable to increment a second count value upon reception of output from the second sensor 4, and to decrement the second count value upon reception of output from the first sensor 2. Discrimination between genuine and erroneous signals is achieved on the basis of the outputs of the first and second counters 1025 104. The circuit is useful with vibration or seismic sensors used for detecting wear in bearings of machinery, or in security systems for detecting terrorist intervention. The undesirable effects of environmental factors such as rain or hail may be avoided since they would be apparent on both sensors and would therefore cancel each other out at the counters.

Description

CIRCUIT, METHOD AND SYSTEM FOR DETECTING TERRORIST INTERVENTION The present invention relates to a circuit, method and system for detecting terrorist intervention. In particular, it relates to a circuit for use with multiple sensors for discriminating genuine sensor signals and erroneous sensor signals.

BACKGROUND OF THE INVENTION

Sensors, such as seismic or vibration sensors, have a variety of uses. For example, vibration sensors can be used to detect wear in bearings of machinery. However, environmental factors may cause unreliable sensor readings, and so it is desirable to be able to discriminate between genuine sensor readings and those caused by common environmental factors.

Sensors, such as seismic or vibration sensors, can also be used for security measures in a variety of situations. For example, a sensor may be used to prevent tampering of various devices or systems. A sensor may also be used to prevent unauthorised access to certain locations, buildings or sites. This is particularly useful for multiple sites that can not be manned 24 hours everyday. This can be particularly advantageous for vulnerable sites such as access to water supplies which could be tampered with by terrorists adding poisonous chemicals to the water supply. These water supply access points are often exposed to the environment. Therefore, it is desirable to avoid unreliable sensor readings caused by environmental factors. For example, a sensor that is positioned in an outdoor location such as a water supply access point may be undesirably activated by environmental conditions such as rain or hail. It is therefore desirable to be able to discriminate between genuine sensor signals and erroneous sensor signals such as those caused by common environmental factors.

SUMMARY OF THE PRESENT INVENTION

The present invention seeks to provide a more effective method for discriminating between genuine sensor signals and erroneous sensor signals.

According to one aspect of the present invention, there is provided a discriminator circuit comprising: a first input for receiving a signal from a first sensor; a second input

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for receiving a signal from a second sensor; a first counter operable to increment a first count value upon reception of a signal from the first input, and to decrement the first count value upon reception of a signal from the second input; and a second counter operable to increment a second count value upon reception of a signal from the second input, and to decrement the second count value upon reception of a signal from the first input, wherein the first counter is operable to produce a first output signal when the first count value reaches a first predetermined value, and wherein the second counter is operable to produce a second output signal when the second count value reaches a second predetermined value.

According to another aspect of the present invention, there is provided a method for discriminating between genuine sensor signals and erroneous sensor signals, the method comprising: upon receipt of a signal from a first sensor, incrementing a first count value and decrementing a second count value; upon receipt of a signal from a second sensor, incrementing the second count value and decrementing the first count value; outputting a first output signal when the first count value reaches a first predetermined value; outputting a second output signal when the second count value reaches a second predetermined value; and discriminating a sensor signal as genuine if either a first or a second output signal is present and discriminating a sensor signal as erroneous if both the first and second output signals are not present.

According to another aspect of the present invention, there is provided a system for discriminating between genuine sensor signals and erroneous sensor signals, the system comprising: a first counter for incrementing a first count value upon receipt of a signal from a first sensor, and for decrementing the first count value upon receipt of a signal from a second sensor; a second counter for incrementing a second count value upon receipt of a signal from a second sensor and for decrernenting the second count value upon receipt of a signal from the first sensor; the first counter outputting a first output signal when the first count value reaches a first predetermined value; the second counter outputting a second output signal when the second count value reaches a second predetermined value: means for discriminating between genuine sensor signals and erroneous sensor signals; and means for activating an alarm upon receipt of a genuine signal.

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In this way, the sensory output is discriminated such that erroneous signals are detected and, as a result, do not generate a warning. The operation of the pair of sensors in combination with the counters minimise false alarms as the sensory output from one sensor may cancel the counter output of the other sensory output such that if both sensors detect a disturbance then this is likely to be as a result of environmental factors and is erroneous. For example, erroneous sensory Outputs as a result of rain or hail on the sensors are detected and discriminatej as being erroneous since these readings are likely to be apparent on both sensors and would therefore cancel each other out at the counters and would provide no output signal. Also, the operation of the pair of sensors in combination with the counters is such that if the detected disturbance is not sustained for a period of time by a single sensor the sensory output is deemed erroneous. The discriminator circuit of the invention provides a simple effective and accurate discrimination between genuine and erroneous signals. Consequently, it avoids false alarms being generated to detect a genuine occurrence of tampering of an access door, for example, for a water supply and prevent terrorist intervention.

The circuit may comprise a reset unit operable to reset the first counter after a first predetermined time period following receipt of a signal from (he first input by the first counter.

The circuit may also comprise a reset unit operable to reset the second counter after a second predetermined time period following receipt of a signal from the second input by the second counter.

In this way, false alarms caused by erroneous vibrations picked up by the sensors over long periods of time are eliminated. In other words, the circuit enables discrimination of genuine signals when the sensory output detects a sustained disturbance.

The first predetermined value and the second predetermined value may be, for example, two. In this way, the sensitivity of the system can be adjusted by adjusting the predetermined value. If the predetermined value is particularly low, such as two, an even more rapid response time is achieved.

* BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference is made to the following description taken in conjunction with the accompanying drawings, in which: Figure 1 is a schematic block diagram illustrating a discriminator circuit embodying one aspect of the present invention; Figure 2 is a flow chart illustrating steps in a method embodying another aspect of the present invention,

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Figure 1 is a schematic block diagram illustrating a discriminator circuit for use with a water supply access, for example, embodying one aspect of the present invention. The discriminator circuit 10 has a first input terminal 101 and a second input terminal 103, which are connected for receiving signals from a first sensor 2 and from a second sensor 4. The first sensor 102 and the second sensor 4 may be located in different places. For example, in the case of bearings of machinery the sensors may be located at different positions on the machinery and in the case of security measures the sensors may be located on different access points.

The circuit includes a first counter 102, a second counter 104 and a reset circuit 106.

The reset circuit 106 has a first reset input terminal 108 for receiving a reset signal Ri from the first input terminal 101 and a second reset input terminal 110 for receiving a reset signal R2 from the second input terminal 103. The first counter 102 has an increment input terminal 112 and a decrement input terminal 114, for incrementing and decrementing respectively a first count value upon receipt of a signal at the appropriate input terminal of the first counter 102. Similarly, the second counter 104 has an increment input terminal 116 and a decrement input terminal 118, for incrementing and decrementing respectively a second count value upon receipt of a signal at the appropriate input terminal of the second counter 104.

In addition, the first counter 102 has a reset input terminal 120 for receiving a reset signal RS1 from the reset circuit 106 and the second counter has a reset input terminal 122, for receiving a reset signal RS2 from the reset circuit 106. When a reset signal is

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received at the reset input terminal 120 and 122, the first and second count values are reset to an initial value, for example zero.

The increment input terminal 112 of the first counter 102 is connected to receive a sensor signal Ii from the first input terminal 101 of the circuit 10. The decrement input terminal 114 of the first counter 102 is connected to receive a sensor signal Dl from the second input terminal 103 of the circuit 10.

The increment input terminal 116 of the second counter 104 is connected to receive a sensor signal 12 from the second input terminal 103 of the circuit 10. The decrement input terminal 118 of the second counter 104 is connected to receive a sensor signal D2 from the first input terminal 101 of the circuit 10.

The circuit 10 has a first output terminal 124 and a second output terminal 126. The first counter 102 is operable to produce a first output value OUTPUT1 on the first output terminal 124 when the first count value reaches a first predetermined value.

The second counter 104 is operable to produce a second output value OUTPUT2 on the second output terminal 126 when the second count value reaches a second predetermined value. The first and second predetermined values may be different or equal to one another. For example, the first and second predetermined values may each be equal to two.

Operation of the circuit illustrated in Figure 1 will now be described with reference to the flow chart of Figure 2.

The sensors 2 and 4 sense vibrations and in the event of increased vibrations, for example, the sensors output respective signals on the output terminals 101 and 103.

The first input terminal 101 of the circuit 10 receives a first sensor signal from the first sensor 2 (step 1001). The second input terminal 103 of the circuit 10 receives a second signal from the second sensor 4 (step 1011).

The increment input terminal 112 of the first counter 102 receives the first sensor signal from the first input terminal 101 of the circuit 10. Upon receipt of the first sensor signal, the increment input terminal Ii increments a first count value (step 1003). The decrement input terminal Dl of the first counter 102 receives the second sensor signal from the second input terminal 103 of the Circuit 10. Upon receipt of the second sensor signal, the decrement input terminal Dl decrements the first count value (step 1013).

The first counter 102 determines whether the first count value has reached a first predetermined value (step 1005). The first predetermined value may be. for example.

two. When the first count value reaches the first predetermined value, the first output 108 of the circuit 10 produces a first output value OUTPUT 1 (step 1007). Upon output of the first output value OUTPUT1, an alarm or an alert is activated. The alarm indicates that the signal received by the sensor is a genuine signal. For example, in the case of bearings in machinery, the alarm may indicate a considerable amount of wear in the bearing causing the vibration. In the case of security measures, the alarm may indicate that a device or system is being tampered with.

The output value may also activate a camera, which can further be used to detect a false alarm. For example, it can be seen from a live camera feed to confirm how critical the situation is. Upon receipt of the alarm or alert, manual intervention can be used and the circuit is reset.

The increment input terminal 12 of the second Counter 104 receives the second sensor signal from the second input terminal 103 of the circuit 10. Upon receipt of the second sensor signal, the increment input terminal 12 increments the second count value (step 1013). The decrement input terminal D2 of the second counter 104 receives the first sensor signal from the first input terminal 101 of the circuit 10. Upon receipt of the first sensor signal, the decrement input terminal D2 decrements a second count value (step 1003).

The second counter 102 determines whether the second count value has reached a second predetermined value (step 1015). The second predetermined value may be, for example, two. When the second count value reaches the second predetermined value, the second output 110 of the circuit 10 produces a second output value OUTPUT2 (step 1017). Upon output of the second output value OUTPUT2, an alarm or an alert is activated.

Upon initiation of the counters, the reset timer is started and if the first and second predetermined value is not reached, the timer continues to run (step 1021) until a predetermined time period has elapsed (step 1023).

Once the predetermined time period has elapsed, the reset circuit 106 outputs a reset signal to the first counter 102 and the second counter 104. The reset signal RS1 is received on the reset input terminal 120 of the first counter 102 and the first count value is reset to an initial value, for example zero (step 1025). Similarly, the reset signal RS2 is received on the reset input terminal 122 of the second counter 104 and the second count value is reset to an initial value, for example zero (step 1025).

In this way, it is possible to effectively and accurately discriminate between genuine sensor signals and erroneous sensor signals. This is achievable since the output signals of the circuit have to be confirmed by one another, making the discrimination between types of signals more accurate and only a low predetermined value needs to be reached before the signals are Output, making the discrimination more time responsive. As a result false alarms are avoided and only genuine events detected such as tampering of an access door for a water supply to tamper with the water supply such as add poisons during a terrorist attack.

Although an embodiment of the present invention have been illustrated in the accompanying drawings and described in the foregoing detailed description, it will be understood that the invention is not limited to the embodiment disclosed, but is capable of numerous modifications without departing from the scope of the invention as set out in the following claims.

Claims

CLAIMS1. A discriminator circuit comprising: a first input for receiving a signal from a first sensor; a second input for receiving a signal from a second sensor; a first counter operable to increment a first count value upon reception of a signal from the first input, and to decrement the first count value upon reception of a signal from the second input; and a second counter operable to increment a second count value upon reception of a signal from the second input, and to decrement the second count value upon reception of a signal from the first input, wherein the first counter is operable to produce a first output signal when the first count value reaches a first predetermined value, and wherein the second counter is operable to produce a second output signal when the second count value reaches a second predetermined value.
2. A circuit as claimed in claim 1, further comprising a reset unit operable to reset the first counter after a first predetermined time period following receipt of a signal from the first input by the first counter.
3. A circuit as claimed in claim 1 or 2, further comprising a reset unit operable to reset the second counter after a second predetermined time period following receipt of a signal from the second input by the second counter.
4. A circuit as claimed in any one of the preceding claims, wherein the first predetermined value is two.
5. A circuit as claimed in any one of the preceding claims, wherein the second predetermined value is two.
6. A method for discriminating between genuine sensor signals and erroneous sensor signals, the method comprising: upon receipt of a signal from a first sensor, incrementing a first count value and decrementing a second count value; upon receipt of a signal from a second sensor, incrementing the second count value and decrementing the first count value; outputting a first output signal when the first count value reaches a first predetermined value; outputting a second output signal when the second count value reaches a second predetermined value; and discriminating a sensor signal as genuine if either a first or a second output signal is present and discriminating a sensor signal as erroneous if both the first and second output signals are not present.
7. A method as claimed in claim 6, the method further comprising resetting the first counter after a first predetermined time period following receipt of a signal from the first input by the first counter.
8. A method as claimed in claim 7, the method further comprising resetting the second counter after a second predetermined time period following receipt of a signal from the second input by the second counter.
9. A system for discriminating between genuine sensor signals and erroneous sensor signals, the system comprising a discriminating circuit as claimed in any one of the preceding claims; means for discriminating between genuine sensor signals and erroneous sensor signals; and means for activating an alarm upon receipt of a genuine signal.
10. A discriminator circuit substantially as hereinbefore described with reference to any one of the accompanying drawings.
11. A system for discriminating between genuine sensor signals and erroneous sensor signals, the system substantially as hereinbefore described with reference to any one of the accompanying drawings.
12. A method for discriminating between genuine sensor signals and erroneous sensor signals, the method substantially as hereinbefore described with reference to any one of the accompanying drawings.