APPENDIX K 

 WAVE MEASUREMENT 



Wave Staff Design. 



A block diagram of the wave staff and associated electronic cir- 

 cuits is shown below: 



Square 



Wave 



Oscillator 





Bilateral 

 Current 

 Source 



'in 



Wave 

 Staff 



% 



Buffer 





Precision 

 AC Detector 

 5 Variable 



Gain 

 Amplifier 











The wave staff itself consists of a length of PVC tubing which is 

 spirally wound with a resistance wire, such that when it is immersed 

 in seawater, the electrical resistance varies in direct proportion to 

 the length of the exposed staff. 



The electronic circuits driving the wave staff consist of a fixed 

 frequency square wave oscillator (having a precisely controlled output 

 amplitude) driving a precision bilateral current source with an output 

 current directly proportional to the input voltage. Thus, the wave 

 staff is driven by a current source of constant magnitude, but one which 

 changes direction with each one-half cycle of the square wave oscilla- 

 tor. The output of the wave staff then is a square wave voltage with a 

 magnitude (peak to peak) that is directly proportional to the length of 

 the exposed wave staff. This output is fed to a high input impedance 

 voltage follower circuit which serves as a buffer between the wave staff 

 and the ac detector circuit. The precision ac detector circuit uses 

 two operational amplifiers in conjunction with two diodes to form a 

 precision full-wave rectifier circuit that is capable of operating at 

 very low input voltages. Ordinary diode detector circuits cannot 

 operate on ac signals of peak magnitude less than the forward voltage 

 drop of the diodes and produce large conversion errors unless the sig- 

 nal magnitude is large with respect to the diode voltage drop. A gain 

 control has been incorporated in the detector circuit so that full-scale 

 output can be set at any positive value up to +10 volts with a wave 

 staff resistance of 300 ohms up to 3,000 ohms. 



Alternating current is used to drive the wave staff to avoid both 

 the corrosion effects that would occur if direct current were used and 

 the dc offset which occurs as a result of the use of dissimilar metals 

 in a conducting solution. The latter is eliminated by use of ac coup- 

 ling in the output from the wave staff. 



Bench tests of the wave staff electronic circuits were made using 

 a 1,000-ohm variable precision resistor in place of the wave staff. The 



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