GB2256042A

GB2256042A - Radio-activity sensor apparatus and system.

Info

Publication number: GB2256042A
Application number: GB9110770A
Authority: GB
Inventors: Keith Taylor; Neil Stewart Brighton; Ravji Valji Bhudia
Original assignee: Siemens Plessey Controls Ltd
Current assignee: Siemens Plessey Controls Ltd
Priority date: 1991-05-18
Filing date: 1991-05-18
Publication date: 1992-11-25
Also published as: GB9110770D0

Abstract

A radio-active sensor unit comprising a plurality of Geiger-Muller tubes (GMT)s each of the said tubes being arranged to cover a different part of a predetermined range of radiation levels, counter means, one for each tube responsive to pulses derived from each tube, and transceiver means operable for transmitting from the sensor unit, data which can be identified by means of a predetermined address, and further operable for receiving control signals addressed to the sensor unit of which the transceiver forms a part. A system can be built up using several sensor units to provide an indication of radiation levels throughout a region of interest, each unit communicating with a central control unit by modem, radio etc. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO RADIO-ACTIVITY SENSOR APPARATUS AND SYSTEMS This invention relates to radio-activity sensor apparatus and systems.

In the event of serious wide spread radio-active pollution as might be a occasioned by a nuclear catastrophe, it is desirable to establish the level of pollution at various locations within a polluted region so that decisions may be taken concerning entry of personnel to the region and/or evacuation of personnel from the region for example.

One object of the present invention is to provide a radioactivity sensor unit suitable for remote operation and a further object of the invention is to provide a system comprising a plurality of radio-activity sensor units which in combination comprise a system, which system facilitates remote monitoring of radio-activity levels at various locations throughout a region of interest.

According to the present invention a radio-active sensor unit comprises a plurality of Geiger-Muller tubes (GMT)s each of the said tubes being arranged to cover a different part of a predetermined overall range of radiation levels covered by the said tubes in combination, counter means one for each tube responsive to pulses derived from each tube for providing data appertaining to the level of radiation sensed by the tubes, a central processor unit (CPU) comprising storage means and being responsive to the said data, first presettable switch means operable for biasing data fed to the CPU from the counters thereby to compensate for differences in sensitivity of the said tubes, second presettable switch means settable to define a predetermined assigned address unique to the sensor unit of which it forms a part and transceiver means operable for transmitting from the said sensor unit, data the origin of which is identified by means of the predetermined address and further operable for receiving control signals addressed to the sensor unit of which the transceiver forms a part.

A plurality of sensor units each having a different assigned address and each being positioned at a different location may be coupled via a data bus to a remotely positioned control unit.

The control unit may include power supply apparatus arranged to feed the said sensor units via power supply lines conveniently combined with the said control bus to form a single cable.

The control unit may be adapted and arranged to address the sensor units sequentially via the data bus whereby serial data appertaining to radiation levels which obtain at each unit is transmitted to the control unit.

Preferably two Geiger-Muller tubes are provided in each sensor unit, the tubes being arranged to feed pulse counters, one for each tube, which are coupled to the CPU via a latch.

The CPU may be operatively associated with an EPROM programmed with data selectable in accordance with the setting of the first presettable switch means to effect the biasing.

Additionally the EPROM may be programmed with data which is accessed by the CPU and which serves to compensate for GMT dead time and non-linearity.

The CPU may be operatively associated with a RAM which serves to facilitate computation by the CPU of dose rate.

The radio-active sensor unit may comprise an BHT unit which serves to convert a low voltage d.c. supply to an EHT voltage for the (GMT)s.

The EHT unit and/or the low voltage d.c. supply may be monitored by a monitor unit which operates to reset the CPU consequent upon a power supply loss or in the event of CPU failure.

The control unit may be operately associated with a local control terminal and/or it may be coupled via a modem to telephone lines and/or via a transceiver to other external data collection and/or control terminal means.

The control unit may be operately associated with a locally positioned computerised weather station.

The control unit may embody battery supply means and a solar panel and a charge controller which serve to recharge the battery supply means.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which Figure 1 is a generally schematic block diagram of a radioactivity sensor unit, and Figure 2 is a generally schematic block diagram of a control unit with which the sensor unit of Figure 1 is operatively associated.

Referring now to Figure 1, a radio-activity sensor unit, sometimes referred to as a probe, comprises two Geiger-Muller tubes 1 and 2 which operates to detect gamma radiation at high and low levels respectively, whereby the two Geiger-Muller tubes 1 and 2 in combination cover a predetermined spread or range of radiation levels. Pulses from the tubes 1 and 2 are fed by lines 3 and 4 respectively to pulse amplifiers 5 and 6 respectively. The pulse amplifiers 5 and 6 are arranged to feed a six stage counter 7 and an eight stage counter 8 respectively, thereby to facilitate the counting of output pulses which originate from the Geiger-Muller tubes 1 and 2. Signals from the counters 7 and 8 are fed via a latch 9 to a central processor unit CPU 10.In order to compensate for non-linearity characteristics of the Geiger-Muller tubes 1 and 2 and to correct for dead time, look up tables are held in an EPROM 11 which is coupled to the CPU 10 via a line 12. The EPROM 11 is also programmed with data which serves to compensate for manufacturing variations in the sensitivity of the Geiger-Muller tubes 1 and 2. Data for providing this compensation is stored in appropriate addresses of the EPROM 11 and presettable sensitivity control switches 12 are provided for selecting an appropriate address in the EPROM 11 during a setting-up procedure.

During this setting-up procedure the tubes 1 or 2 are exposed to a high or low level radio-active source as appropriate and the presettable switches 12 are then adjusted to provide an appropriate output signal from the CPU 10.

In order to test operation of the counters 7, and 8, a facility for injecting test pulses to the amplifiers 5 and 6 from the CPU via a line 10a is provided. Output signals from the CPU 10 are fed on a line 14 to a transceiver 15, output signals from which are fed on a line 16 to a remotely positioned control unit 24 shown in Figure 2. The line 16 serves also for carrying return signals from the control unit 24 for control and/or test purposes.

In order to identify output signals transmitted from the unit on the sensor line 16, the signals are 'labelled' with an appropriate address which is set in accordance with the setting of presettable address switches 17 which are set to provide appropriate unique address data for the CPU 10. The counters 7 and/or 8 are arranged to count for a five second period. The count registered is read by the CPU 10 via the latch 9. The five second count data signals are converted in the CPU 10 to data appertaining to dose rate and count per second, the calculation appertaining to dose rate etc being facilitated by means of a random access memory unit 13 which is coupled to the CPU 10.

An EHT voltage for the Geiger-Muller tubes 1 and 2 is derived in an EHT unit 18 which provides a voltage on a line 19 of about 600 volts for the Geiger-Muller tubes. The EllT unit 18, in common with the other electrical components of the sensor unit receives a low voltage power supply on a line 20 from a stabilised low voltage power supply unit 21. The power supply unit 21 is fed from a DC power supply line 22 which is fed from the remote control unit 24 shown only in Figure 2. A monitor or 'watch dog' unit 23 is provided which serves to monitor operation of the CPU 10 and the power supply units 18 and 21 so that in the case of power failure or a CPU 10 'crash', the CPU 10 can be reset until such time as power is reestablished or normal working of the CPU 10 re-established.

Referring now to Figure 2, a radio-activity sensor unit of the kind described in Figure 1 is shown in Figure 2 as a probe 23. The sensor unit or probe 23 comprises a generally cylindrical aluminium housing which is about 630 millimetres long and 100 millimetres in diameter. The various parts of the sensor unit of Figure 1 are resiliently mounted within the tube whereby a certain degree of shock resistance is afforded. Connections to and from the unit such as the lines 16 and 22 are effected via an environmentally sealed bulkhead connector not shown.

In order to monitor radio-activity throughout a predetermined region, a plurality of radio-active sensor units each as shown in Figure 1 are provided, each being placed in communication with a central control unit 24 as shown in Figure 2 via a serial data transmission/reception line 25. The control unit 24 may be adapted for operation via a local terminal unit 25 and may embody or have associated with it a printer 26. Additionally or alternatively the control unit 24 may be coupled to a telephone network via a modem 27. Moreover facilities are provided for transmission of data derived from the control unit 24 by a radio transceiver 28.

Thus the control unit 24 may be operated locally via the local terminal 25, or remotely via the modem 27, or via the radio transceiver 28. In addition to data received from radio-activity sensor units such as the sensor unit 23, data may also be provided by computerised weather stations such as the station 29 which is shown schematically and which is coupled to the control unit 24. The control unit 24 and its associated equipment would normally receive electrical power via a mains power line 30 but in order to provide power under emergency conditions a solar panel 31 having an associated charge controller 32 may be provided for topping up the charge of a locally provided battery system (not shown) via a line 33.

Various modifications may be made to the arrangement hereinbefore described without departing from the scope of the invention and for example although a serial data transmission system is contemplated for communication with the sensor unit shown in Figure 1, alternative methods of data transmission may be provided in alternative embodiments.

Additionally it is contemplated that the control unit 24 may form a small part of a much larger overall system embodying a plurality of control units each corresponding to the control unit 24, each control unit being used to cover a particular region and having under its control a plurality of radiation sensor units such as the probe 23 together with other sensor apparatus such as the weather station 29. Thus each control unit of the overall system may be used to provide information relating to weather conditions obtaining in its own particular region and for example data appertaining to barometric pressure, temperature, precipitation or wind force and direction may be provided, whereby a country wide picture can be built up using information from the control units of the overall system which may be monitored or controlled from a national control terminal for example.

Claims

1. A radio-active sensor unit comprising a plurality of Geiger Muller tubes (GMT)s each of the said tubes being arranged to cover a different part of a predetermined overall range of radiation levels covered by the said tubes in combination, counter means one for each tube responsive to pulses derived from each tube for providing data appertaining to the level of radiation sensed by the tubes, a central processor unit (CPU) comprising storage means and being responsive to the said data, first presettable switch means operable for biasing data fed to the CPU from the counters thereby to compensate for differences in sensitivity of the said tubes, second presettable switch means settable to define a predetermined assigned address unique to the sensor unit of which it forms a part and transceiver means operable for transmitting from the said sensor unit, data the origin of which is identified by means of the predetermined address and further operable for receiving control signals addressed to the sensor unit of which the transceiver forms a part.

2. A sensor unit as claimed in Claim 1, wherein two Geiger-Muller tubes are provided, the tubes being arranged to feed pulse counters, one for each tube, which are coupled to the CPU via a latch.

3. A sensor unit as claimed in Claim 2, wherein the CPU is operatively associated with an EPROM programmed with data selectable in accordance with the setting of the first presettable switch means to effect the biasing.

4. A sensor unit as claimed in Claim 3, wherein the EPROM is programmed with data which is accessed by the CPU and which serves to compensate for GMT dead time and non-linearity.

5. A sensor unit as claimed in Claim 4, wherein the CPU is operatively associated with a RAM which serves to facilitate computation by the CPU of dose rate.

6. A sensor unit as claimed in Claim 5 comprising an EHT unit which serves to convert a low voltage d.c. supply to an EHT voltage for the (GMT)s.

7. A sensor unit as claimed in Claim 6, wherein the EHT unit and/or the low voltage d.c. supply is monitored by a monitor unit which operates to reset the CPU consequent upon a power supply loss or in the event of CPU failure.

8. A system comprising a plurality of sensor units each as claimed in any preceding claim, each having a different assigned address and each being positioned at a different location, coupled via a data bus to a remotely positioned control unit.

9. A system as claimed in Claim 8, wherein the control unit includes power supply apparatus arranged to feed the said sensor units via power supply lines combined with the said control bus to form a single cable.

10. A system as claimed in Claim 8 or Claim 9 wherein the control unit is adapted and arranged to address the sensor units sequentially via the data bus whereby serial data appertaining to radiation levels which obtain at each unit is transmitted to the control unit.

11. A system as claimed in Claim 8, Claim 9 or Claim 10, wherein the control unit is operatively associated with a local control terminal and/or coupled via a modem to telephone lines and/or via a transceiver to other external data collection and/or control terminal means.

12. A system as claimed in any of Claims 9 to 11, wherein the control unit is operately associated with a locally positioned computerised weather station.

13. A system as claimed in any of Claims 9 to 12, wherein the control unit is arranged to embody battery supply means and a solar panel and a charge controller which serve to recharge the battery supply means.

14. A sensor unit substantially as hereinbefore described with reference to the accompanying drawings.

15. A system embodying sensor units, each as claimed in Claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.