In order to monitor the structural integrity of the array and 

 provide engineering data, a tensiometer is placed in Station 4. 



The sampling rate for data storage is adjustable commensurate 

 with the experiment. The data may also be monitored continuously 

 with auxilary equipment. All sensors have performed extremely 

 well throughout testing and since the October 1968 deployment. 



3.2.1 Transducer Circuitry 



The pressure, tension, and temperature transducers, as dis- 

 cussed in this section, manifest a change in resistance propor- 

 tional to the magnitude of the quantity that they sense. This change 

 in resistance is a very small quantity and, therefore, cannot be 

 measured with conventional ohmmeters or voltmeters with sufficient 

 precision. Consequently, each transducer is made part of a bridge 

 circuit that is capable of measuring resistance to the required 

 accuracy. The bridge circuit is described in Section 3.3 as an 

 element of the Data Acquisition System. The wiring schematic is 

 given in Figure 3-15. A standard two-wire technique is adequate 

 because of the small size of lead wire resistance errors relative 

 to sensor resistance variations. A disadvantage of the system used 

 is that even high impedance shorts due to water penetrations cannot 

 be tolerated. 



3.2.2 Temperature Sensors 



At the depth of the measuring station, the transducers are exposed 

 to small temperature changes. Thus, in measuring the temperature 

 of the water to determine the presence of an internal wave, the reso- 

 lution and time of response of the transducer are the critical design 

 parameters, with the overall absolute accuracy and stability with 

 time requirements being somewhat relaxed. Many electrical-type 

 temperature sensing devices are available, including the thermistor, 

 thermocouple, and various metallic sensor elements. However, be- 

 cause of the design parameter requirements, the thermistor is most 

 suitable and is most compatible with a Wheatstone Bridge circuit. 



The thermistor we are using is the Fenwal Electronics, Inc., 

 Type D-10 Oceanographic Sub-Mini- Probe, encapsulated lOOK at 

 25°C Iso-curve Thermistor. This particular thermistor meets all 

 design requirements. It is designed to have an accuracy predictable 



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