NUCLEAR DIGITAL TRANSDUCERS 



J. L. HYDE 

 Charter Laboratories 

 Division of Charter Wire, Inc. 

 Northport, L. I., New York 



ABSTRACT 



Measurement transducers whose signal output is 

 a pulse rate, derived by modulation of the radia- 

 tion from a nuclear source, are an unconventional 

 type now being developed in this laboratory. 

 Analog to pulse rate conversion is performed in 

 the sensing head essentially by mechanical means . 

 A digital readout is obtained by means of a pulse 

 counter . 



accumulate a digitized total count, are now 

 available. Among these are: (l) tachometers and 

 flowmeters (including anemometers and ocean cur- 

 rent meters) of the "toothed wheel" or revolution 

 counting type, (2) the vibrating wire type of 

 pressure transducer and (3) DC analog transducers 

 in combination with a voltage controlled oscil- 

 lator which generates a frequency analog. Nuclear 

 digital transducers represent a fourth type. 



These transducers can be designed for measure- 

 ment of any physical variable that is sensed 

 through a mechanical displacement. Two develop- 

 mental models are described and test results are 

 presented. Proposed applications include digital 

 pressure and temperature transducers and a digital 

 bathythermograph . 



INTRODUCTION 



This paper describes our development work on 

 measurement transducers based on the inherently 

 discrete or digital properties of radioisotope 

 decay. It had seemed apparent that transducers 

 of this nature would permit physical data to be 

 digitized substantially at the source, thus pre- 

 serving the initial sensing accuracy during 

 telemetry and data processing. It had also 

 appeared that a transducer could be built which, 

 once calibrated during assembly, would retain its 

 accuracy indefinitely. These impressions have 

 been reinforced by our experience to date. It 

 now seems likely that the special features inher- 

 ent in these devices may be especially attrac- 

 tive in the design of measurement transducers 

 for the marine sciences . 



The basic principle of a nuclear digital trans- 

 ducer is so unsophisticated that it is not 

 entirely clear why somebody did not try to build 

 one long ago. Two of the most plausible reasons 

 are that digital data were not in any great 

 demand and that silicon junction nuclear par- 

 ticle detectors, which are particularly suitable 

 for these transducers, were not previously avail- 

 able. Therefore, it is unlikely that a useful 

 device could have been built until quite recently. 



Several types of pulse count transducers, 

 for which a time base is generated in order to 



FUNCTIONAL DESCRIPTION 



A digital transducer has been defined-'- as a 

 coupling device which passes data along in some 

 form of discrete code to an unlike system or sub- 

 system. In a nuclear digital transducer, the 

 data are transmitted by means of nuclear particles 

 or by electrical pulses derived from nuclear par- 

 ticles and the coding is accomplished by counting 

 a variable but predetermined fraction of the dis- 

 integrations occurring in a radioactive source. 

 Most nuclear transducers, including various types 

 of thickness and density gauges, are analog in 

 nature owing to the fact that a DC analog signal 

 is developed by pulse integration within the 

 detector. 



When nuclear radiation intensity or radiation 

 flux density is measured by a Geiger counter, 

 either a DC analog or a pulse rate analog can be 

 used to indicate the radiation level. In the 

 latter case, when a pulse counter including a 

 time base is used for readout, the combined instru- 

 ment is similar to a nuclear digital transducer. 

 In other applications where the nuclear digital 

 method might have been used, for example in some 

 of the thickness gauges, the DC analog method 

 seems to have been preferred. 



A block diagram of a nuclear digital trans- 

 ducer is shown in Fig. 1. Particles from the 

 nuclear source pass through the variable aperture 

 controlled by the shutter and reach the detector 

 where they generate electrical pulses. These 

 pulses are counted by a conventional type of 

 digital counter over a preset time base. 



The mechanical sensor controls the size of the 

 aperture through which the particles pass. In 

 the case of a pressure transducer this may be a 

 bourdon tube or bellows. In the case of a 



Superior numbers refer to similarly numbered references at the end of this paper. 



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