MWJEPS REPORT 76^0 



Pressure . Depth measurements in the ocean can be made by observing 

 the effect of pressure on a pair of reversing thermometers, one pro- • 

 tected and the other \inprotected from pressure (Ref. 5)> A great 

 advantage of this method is its accuracy, but a serious disadvantage is 

 that only point-depth readings are provided. The thermometers can only 

 be read by visual inspection at the surface and only one reading taken 

 for each depth point. The probable error of depths obtained by the 

 xinprotected thermometer is about +^5 meters for depths of less than 

 1,000 meters, and about 0.5^ of the wire depth for depths greater than 

 1,000 meters (Ref. 5). 



Other methods of reading pressure to determine ocean depth are as 

 follows: spring-loaded bellows. Bourdon tube (a hollow spring), 

 electrical strain gage, variable -reluctance gage, diaphragm-actuated 

 electrical potentiometer, vibrating-wire transducer, and more recently 

 the solid-state pressure sensitive gage. All may yield a variable 

 voltage, current, or frequency as a function of pressiH'e, and con- 

 sequently are suitable for use in a continuous depth- reading meter. 

 Accuracy of about Vfa may be attained by each of these methods . The 

 vibrating wire transducer was selected for the NOTS-SVTP instrxmient 

 because of its accuracy, frequency-modulated output, and repeatability and 

 simplicity of its associated circuitry. 



Pressure readings in the ocean by the SVTP instrument yield con- 

 tinuous readings within Vjo of the range of the . Vibrotron used (available 

 in ranges from 100 to 10,000 psi). The resulting error is slightly 

 greater than the O.^'jo of protected-unprotected reversing thermometer 

 pairs . 



DESCRIPTION 



Figure 2 is a block diagram of the NOTS-SVTP instrument. The out- 

 puts of the velocity-of-sound, tenrperature, and pressure oscillators 

 are summed and amplified to drive the cable . 



The individual circuits and packaging of the instrument are 

 described in the following sections . 



SOUND-VELOCITY OSCILLATOR 



Figiire 3 Is a diagreim of the transistorized sound-velocity circuit 

 used in the SVTP insti-uraent. The circuit is essentially that designed 

 by NBS with minor modifications (Ref, 1 and 6). It has been described 

 as a "sing around" or "an ultrasonic delay line that synchronizes a 

 relaxation oscillator," i.e., the circuit consists of a free-running 



