COMPUTERS AND TRANSDUCERS 



P. F. SMITH 

 Geodyne Corporation 

 Waltham, Massachusetts 



E. FREDKIN 

 Information International 

 Maynard, Massachusetts 



INTRODUCTION 



In this paper, the term "transducer" is used 

 in its broadest sense as the whole link between 

 the natural phenomenon and digital results pre- 

 sented in interpretable form. It will be shown 

 that this use is justified by the unique role 

 the computer can perform in a particular data- 

 acquisition cycle. In this case, that which is 

 "plugged into" the environment is the Richardson 

 current meter and that which is "plugged into" 

 the computer is the film record from this current 

 meter. The computer which provides the processed 

 data is the PDP-1 (Programmed Data Processor-l) , 

 a single address, single instruction stored pro- 

 gram machine built by Digital Equipment Corpora- 

 tion. 



THE TRANSDUCER 



The current meter (Fig. l) uses fiber optic 

 digital 16 mm film recording of 7-level encoding 

 disc sensing of both vane and compass positions 

 and a 1:1 and 10:1 light chopper sensing the 

 Savonius rotor revolutions. The resulting digi- 

 tal format is illustrated in Fig. 2 where a sec- 

 tion of an original test film strip is reproduced 

 along with high-contrast negative and high- 

 contrast positive prints . Test films are made 

 by operating the instrument on a revolving plat- 

 form. A fan drives the rotor in air. Note that 

 there is a continuous or reference channel in 

 addition to the 16 data channels and, not shown, 

 a read pulse channel for interval recording. A 

 variety of films were tested, including sound 

 recording stock, to determine the most satisfac- 

 tory for reading. The high-contrast positive 

 print proved best. 



Prints of 3 sections of an actual record are 

 shown in Fig. 3- The bit packing density is 

 extremely conservative across the film and could 

 easily be doubled without changing the optical 

 fiber or film image size. Along the film there 

 can be resolved approximately 200 bits per inch. 

 Thus, there are 200 sets of three Vfo numbers per 

 inch or some ^,600 bits. When recording con- 

 tinuously, the 100 feet of film in the instrument 



Fig. 1. 



Superior numbers refer to similarly numbered references 



Richardson current meter: left-complete 

 unit, center- internal mechanism, 

 right-pressure case and vane cage. 



at the end of this paper. 



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