WIRE ROPE 

 TERMINATION 



RESISTANCE ELEMENT 

 TERMINATION 



THIMBLE 



Fig. 3- Termination at top of active element. 



CABLE 

 CLAMP 



14 15 



Fig. k. Section of wire resistance wave sensor. 



is terminated in an eye through the use of a 

 stainless steel thimble and cahle clamp. The 

 upper end is terminated with a simple device con- 

 structed of linen base phenolic material that 

 meets both physical and electrical requirements 

 (Fig. 3)- A pair of single conductor waterproof 

 connectors are used to provide electrical connec- 

 tion of the active element to the deck unit. A 

 photograph of the active element is shown in 

 Fig. k. 



provided by a constant voltage oscillator driving 

 a constant current amplifier. The 1 Kcps oscil- 

 lator, a twin "T" type incorporating a temperature 

 compensated automatic gain control loop, generates 

 approximately one volt rms of a low distortion, 

 amplitude stable sinusoid. This voltage is 

 amplified by 10 and made to approach a constant 

 current source by the constant current amplifier. 

 Since the sea water acts as a resistance short, 

 the voltage developed across the staff will be 

 linearly proportional to the length out of water 

 only if the staff is excited by a constant cur- 

 rent source. The constant current amplifier ful- 

 fills this requirement at the high excitation 

 level of 10 volts rms with the staff out of water. 

 High level sinusoidal excitation minimizes degra- 

 dation of performance due to electrolysis, marine 

 fouling, 60 cps line pickup and induced noises 

 in general. 



The voltage across the staff, which varies 

 linearly with the percent immersion, need only be 

 converted to a form compatible with existing 

 telemetry, digitizing and recording equipment. 

 An AC-DC converter working into a low pass filter 

 performs this function. This converter consists 

 of a high gain operational amplifier with sili- 

 con rectifier diodes enclosed in its feedback 

 path. The low pass filter is a 2-stage LC type 

 which acts to eliminate the pulsating effects of 

 the diode rectification. The output voltage is a 

 ripple free DC voltage which varies from to 5 

 volts depending on the staff immersion. The con- 

 version accuracy is better than to.l^i of full 

 scale. The output also can be DC isolated from 

 sea water ground to eliminate common mode voltages 

 from the output signal. 



PRINCIPLES OF OPERATION 



A block diagram of the electronics is shown 

 in Fig. 5- Excitation for the staff is 



95 



