DESIGN DETAILS 



The Pressure Transducers 



The heart of a system, of this type is, of course, the transducers 

 used to sense the unknown variable. Depth is measured by sensing pres- 

 sure, and it was necessary to obtain a pressure transducer that could 

 be used in the range of to 1,200 feet, 0-537 pounds per square inch 

 gage (p.s.i.g.), with less than 1-percent inherent error, including 

 hysteresis. Inasmuch as the oscillator to be controlled was planned 

 as a highly stable R-C type, it was desirable to have a pressure trans- 

 ducer th?.t was a potentiometer suitable for use in the proposed cir- 

 cuitry. The pressure transducer chosen was a Model 304 miniature gauge 

 pressure potentiometer, manufactured by Bournes Laboratories, Inc. , of 

 Riverside, Calif. 



The R-C oscillator circuitry required two resistance arms, which 

 necessitated the use of two units. The chosen pressure range was from 

 to 600 p.s.i.g., which would allow a maximum depth of 1,340 feet. 

 The use of two pressure potentiometers resulted in less friction and 

 hysteresis than would be possible to obtain in one unit with dual 

 resistance elements. 



In order to prevent exposure of the Bourdon elements of the pres- 

 sure potentiometers to salt water, a hydraulic system employing an 

 intermediate liquid (glycerine) and a rubber bulb was utilized. 

 Because of the possibility of air entrapment, the Bourdons and the 

 hydraulic tubing were filled under vacuum with glycerine. Annealed 

 copper tubing was used, and all fixed joints were silver soldered. 



ELECTRONIC CIRCUITS 



Transmitter 



The transmitter contains 6 vacuum tubes, 2 germanium diodes, 

 and 1 neon voltage regulator. It generates a frequency and amplitude 

 modulated carrier between 21 and 36 kc., at a power level of 1 to 

 2 watts. The unit is completely self-contained and will operate 

 continuously for as long as 15 to 20 hours on one battery loading. 

 (See fig. 2.) 



Considerable time was spent investigating the relative merits 

 of the many types of variable- frequency oscillators in order to choose 

 a design for the depth oscillator that would provide accuracies within 

 the prescribed limits. Finally, an R-C oscillator, whose tuned circuit 

 has the configuration of a Wien bridge, was chosen. This type of 

 oscillator permits the use of the above-mentioned pressure potentio- 

 meter as control elar.ents, thereby simplifying the mechanical con- 

 struction. 



