F-4 



will give a null; however, they yield reciprocal headings. The gaps in 

 the commutator are about k degrees wide; hence the vehicle "follows" the 

 gyro to within about 2 degrees. Rudder action is infrequent during straight 

 runs, and power consumption is small. Rudder solenoid activation is 

 recorded on the vehicle's tape recorder. 



In broad outline all depth systems function in a similar manner: 

 a reference voltage proportional to the desired depth is generated, a 

 voltage proportional to the actual depth is provided by a sensor, and 

 the difference between the signals constitute the error signal which 

 drives the vehicle in the appropriate 'direction to reduce the error to 

 zero. The error signal is limited in amplitude and combined with a pitch 

 sensor signal to keep climb and dive angles within bounds. 



In the SPURV system the depth sensor does not provide a voltage directly, 

 but provides a digital number proportional to depth. The most significant 

 8 bits of the number are compared with a switch-selected digital reference. 

 The resulting "coarse" error signal overrides others until the vehicle is 

 within 30 meters of the desired depth. The lesser 10 bits are converted 

 to an analog voltage and compared against a reference voltage to provide 

 the "fine" error signal. The fine error is nulled when the depth error is 

 less than 0.03m (0.09 ft). 



A new count is generated 12 times a second. If properly stabilized 

 before use by two days of warmup, the Vibrotron will be stable over a 

 6-hour period within 0.1m (0.3 ft) and its repeatability from day to 

 day will be within 0.5ni (1.6 ft). 



Instrumentat ion : The standard nose probe package for SPURV for some years 

 included three elements: a velocimeter (sound velocity), a quartz 

 thermometer and a thermistor-controlled Wien bridge oscillator (WBO). 

 All of the elements are individually packaged for depths up to 3,0H8m 

 (10,000 ft) and they all generate frequencies which are measured and recorded 

 in the instrumentation chassis. 



The velocimeter is a sing-around type manufactured by Lockheed and 

 has a resolution of 0.013 meter per second. 



The quartz crystal thermometer is a relatively slow instrument of 

 high accuracy. The crystal is made by Gulton (Model MET-2) and has a 

 specified accuracy of plus or minus 0.01 degrees C over a 6-month period. 

 The resolution of the thermometer is 0.00056 degrees C. 



The thermistor of the Wien bridge oscillator is made by VECO (type 

 Z32A91) and constitutes the resistive element in an oscillator designed 

 at the Laboratory. 



Another probe configuration contains a fluorometer developed at APL 

 for detecting minute quantities of certain fluorescent dyes in water. 

 The dyed water flows through the instrument's test cell where it is 

 illuminated with light capable of exciting the fluorescence. The 

 scattered fluorescent light is filtered out and focused onto a photo- 

 multiplier tube. The resulting current from the tube is amplified and 

 converted to a frequency. The instrument can measure Rhodamine B dye 

 concentrations ranging from 10 to the minus twelth to 20 to the minus sixth 

 g/cu cm. It uses four overlapping ranges to cover this dynamic range. 

 The fluorometers have been used successfully in three experiments: 



