GB2252819A

GB2252819A - Signal detector apparatus

Info

Publication number: GB2252819A
Application number: GB9103071A
Authority: GB
Inventors: Keith Sutton; Christopher Cranston; Neil Cleverly
Original assignee: Siemens Plessey Controls Ltd
Current assignee: Siemens Plessey Controls Ltd
Priority date: 1991-02-13
Filing date: 1991-02-13
Publication date: 1992-08-19
Also published as: GB9103071D0

Abstract

A detector arrangement comprising an electrical signal detector (1) and an inhibitor including a transducer responsive to a mechanical shock (7) for producing an electrical inhibit signal, which inhibit signal serves temporarily to inhibit operation of the said signal detector. Thus spurious electrical signals produced by mechanical shock or vibration are not registered by the signal detector. As described the output of a dosimeter is inhibited when the response of a piezo-electric shock sensor reaches a pre-deterrnined threshold. <IMAGE>

Description

SIGNAL DETECTOR APPARATUS This invention relates to electrical signal detection apparatus and more especially but not exclusively it relates to such apparatus which forms a part of a dose meter or doserate meter for detecting radioactivity.

In order to detect and/or measure small charges or voltages associated with small charges of the order of a few pico-coulombs, highly sensitive apparatus is required and in use of such sensitive apparatus problems can arise due to the detection of spurious signals caused by mechanical shock or vibration. These spurious signals may for example be caused by small capacitance or inductance changes occasioned by mechanical shock or vibration.

It is an object of the present invention to provide an electrical signal detector which does not respond to spurious electrical signals caused by mechanical shocks or the like.

According to the present invention electrical signal detection apparatus comprises an electrical signal detector and an inhibitor including a transducer responsive to a mechanical shock for producing an electrical inhibit signal, which inhibit signal serves temporarily to inhibit operation of the said signal detector.

Thus with an arrangement according to the invention spurious electrical signals produced by mechanical shock or vibration are not registered by the signal detector.

The inhibitor may include a gate responsive to the electrical inhibit signal for inhibiting operation of the signal detector.

The signal detector may be fed with input signals via the gate, the gate being opened by the electrical inhibit signal.

The electrical signal detector may comprise an integrator which serves to integrate input signals fed thereto via the gate.

The electrical signal detector may include a display unit which serves to provide a visual display indication of the amplitude of an integrated signal produced by the integrator.

The electrical signal detector may include an alarm device and a discriminator or threshold detector, the alarm being operated consequent upon the integrated signal amplitude exceeding a predetermined amplitude as sensed by the discriminator or threshold detector.

The arrangement may form a part of a dose meter or doseratemeter for measuring radioactivity and include a radiation detector element or elements which feed the electrical signal detector with signals for detection.

The radiation detector and the transducer may be mounted so as to receive similar shocks or vibration.

Thus the radiation detector and the transducer may both be mounted in the same plane, on a printed circuit board for example.

The inhibitor may include a delay device whereby a signal path from the radiation detector is delayed with respect to a signal path from the transducer or vibration detector.

The delay device is included to ensure that if the transducer, which serves as a vibration detector sensor is slower than the radiation detector, false signals are still inhibited and not registered by the said electrical signal detector.

The radiation detector may be arranged to feed the electrical signal detector via a further threshold detector or discriminator which serves to inhibit signals below a predetermined amplitude.

The transducer may be a piezo electric device.

The piezo electric device may comprise an active element of the alarm device adapted to provide an audible alarm signal.

Although electrical signals for detection may be provided by a radiation detector in a dose meter, they may be provided by other means in alternative embodiments of the invention.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawing which is; a block schematic diagram of a dose meter.

Referring now to the drawing, a dose meter comprises a radiation detector consisting of a silicon detector 1 which produces an output signal in response to exposure to radioactivity. The output signal is fed through an amplifier/discriminator 2 via a delay device 12 which feeds an integrator 3 via a gate 4. The integrator 3 serves to integrate with time electrical signals produced by the silicon detector 1 in response to exposure to radioactivity, a display unit 13, which may be a liquid crystal display unit, being provided which serves to afford a display indicative of the level of the integrated signal in the integrator 3, thereby to provide an indication of accumulated radiation dose.The signal from the integrator 3 is fed also to a discriminator 5 which provides an output signal for an alarm driver amplifier 6 when the level of the integrated signal exceeds a predetermined threshold. The driver amplifier 6 is arranged to feed an audible alarm sounder device 7 which includes a piezo electric component as an active element.

As well as providing an audible alarm, the piezo electric device 7 includes an active component which serves as a transducer to provide a signal for a further discriminator/threshold detector 8 which feeds the gate 4.

In operation of the apparatus, if the piezo electric component of the sounder 7 is subjected to shock, as for example might be produced if the apparatus were knocked or dropped, this produces an electrical output signal on a line 9 for the discriminator/threshold detector 8 and if the signal on the line 9 exceeds a predetermined threshold level as determined by the said discriminator 8, a signal is fed from the said discriminator and on a line 11 to the gate 4 temporarily to inhibit the passage of signals from the amplifier/ discriminator 2 to the integrator 3. The delay device 12 ensures that any spurious signals do not pass through the gate 4 before it can operate to inhibit them.

The integrator 3 may for example be a counter which counts pulses produced by the discriminator 2 consequent upon exposure of the detector to radioactivity.

Thus it will be appreciated that spurious signals, as may be produced by the silicon detector 1 due to shock or vibration, are inhibited as the gate 4 is opened.

The piezo electric element of the alarm sounder 7 and the silicon detector 1, may advantageously be mounted on a printed circuit board in the same plane so as to receive similar vibration or shock.

The present arrangement is particularly advantageous since the alarm sounder 7 serves not only for alarm purposes but also for inhibiting spurious signals which might otherwise add to the integration level produced by the integrator 3.

Although in the present example, spurious signals are in effect dumped when the gate is opened, it is contemplated that in an alternative arrangement, an average signal my be substituted, based on previously detected signal levels whereby the integration process is not interrupted.

Additionally, although in the present example a piezo electric device has been used it will appreciated that any other suitable transducer which will produce an electrical signal when subjected to shock may alternatively be employed. It should be understood that although the use of a piezo electric transducer to produce an inhibit signal is in the present example applied to a dose meter, in alternative arrangements a transducer may be used wherever it is required to prevent signals produced by shocks or vibration from being spuriously detected.

Various modifications may be made to the arrangement just before described without departing from the scope of the invention and for example the integrator 3 and the discriminator or threshold detector 5, together with the gate 4, may conveniently form a part of a microprocessor unit, as shown by a broken line 10, the microprocessor unit 10 being arranged to perform other functions as may be required in accordance with the application in view.

Claims

1. Electrical signal detection apparatus comprising an electrical signal detector and an inhibitor including a transducer responsive to a mechanical shock for producing an electrical inhibit signal, which inhibit signal serves temporarily to inhibit operation of the said signal detector.

2. Apparatus as claimed in claim 1 wherein the inhibitor includes a gate responsive to the electrical inhibit signal for inhibiting operation of the signal detector.

3. Apparatus as claimed in claim 2, wherein the electrical signal detector is fed with input signals via the gate, the gate being opened by the electrical inhibit signal.

4. Apparatus as claimed in claim 3 wherein the electrical signal detector includes an integrator which serves to integrate input signals fed thereto via the gate.

5. Apparatus as claimed in claim 4 wherein the electrical signal detector includes a display unit which serves to provide a visual display indication of the amplitude of an integrated signal produced by the integrator.

6. Apparatus as claimed in claim 5 including an alarm device and a discriminator or threshold detector, the alarm being operated consequent upon the integrated signal amplitude exceeding a predetermined amplitude as sensed by the discriminator or threshold detector.

7. Apparatus as claimed in claim 5 or claim 6 which forms a part of a dose meter or doseratemeter for measuring radioactivity and which includes a radiation detector element or elements which feeds the electrical signal detector.

8. Apparatus as claimed in claim 7 wherein the radiation detector and the transducer are mounted so as to receive similar shocks or vibration.

9. Apparatus as claimed in claim 8 wherein the radiation detector and the transducer are both mounted in the same plane.

10. Apparatus as claimed in claim 9 wherein the radiation detector is arranged to feed the electrical signal detector via a further threshold detector or discriminator which serves to inhibit signals below a predetermined amplitude.

11. Apparatus as claimed in any preceding claim wherein the transducer is a piezo electric device.

12. Apparatus as claimed in claim 11 wherein the piezo electric device comprises an active element of the alarm device adapted to provide an audible alarm signal.

13. Apparatus as claimed in claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.