Figure 42 shows the pressure compensation system. No was chosen as the pressure 
compensating gas to avoid oxidation of motor brushes and other electronic components. 
Two 225 ft3 nitrogen flasks were borrowed and a scuba regulator and bleeder valve 
were purchased. The two back-to-back check valves, installed in parallel, were spring loaded 
to between 3 and 4 psi. They served to prevent the pistons from pumping out the N32 gas 
through the scuba valve. 
The internal pressure variation during a cycle was estimated as plus and minus 1.4 
psi at the 500-ft depth. The maximum inertial force due to the acceleration of the water- 
loaded pistons was estimated to be equivalent to 2.45 psi on the two piston faces. These 
numbers led to the selection of plus 5 psi internal operating pressure to ensure that no force 
reversals would occur on the drive system during operation. The bleeder valve ensured that 
the internal pressure would exceed the ambient pressure by 5 psi soon after a depth change. 
The 5 psi differential pressure transducer was tested and the output voltage was 
verified to be 1 volt per psi of differential pressure. 
A l-ohm power resistor was installed in series with the drive power and was 
equipped with a low-pass filter so that the average drive current could be indicated by a dig- 
ital voltmeter. 
Figure A3 shows the arrangement of equipment used for the tests. The transducer 
was submerged at the end of NOSC Pier B to verify the proper operation of the pressure 
system. 
A pickup truck equipped with a shelter was obtained from Public Works to transport 
the equipment and author from Naval Ocean Systems Center to Bayview, Idaho and back. 
This saved about $1,300 of project funds that would have been spent on shipping, air fare 
and car rental. 
“PROCEDURE 
The test facility was closed on Monday, 19 May 1980, due to the fallout of voicanic 
ash from the 18 May eruption of Mt St Helens in Washington state. On Tuesday, 20 May 
1980, L Teston, one of the operators, was able to get to work and we loaded the equipment 
on a boat and transported it to the test barge. 
It took about 2 hours to wash the volcanic ash from the work area, and the 
transducer was then rigged so that the pressure system could be submerged 11.5 feet below 
the axis of the pistons to supply the 5 psi of internal overpressure when the transducer was 
submerged. 
Figure A4 shows how the monitor hydrophone was suspended on a compliant 
support | metre from the center of the axis between the pistons. 
: The in-air test was performed with the pistons just out of the water but with the 
scuba regulator deep enough to supply most of the 5 psi overpressure. The test was repeated 
with the transducer at 25, 100, 150, and 500 ft. The monitor hydrophone output was re- 
corded on an HP 3960 FM tape recorder, and a spectrum of the monitor hydrophone output 
was made at each depth. 
The drive voltages and currents were tabulated for each depth. After the initial 
500-ft test, the transducer was left running throughout the night and into the next morning 
fora total of 18 hours. Seven spectrums of the moniter hydrophone output were recorded 
during the operation at 500 ft. along with tabulations of drive voltage and current. 
CIES AUNT ALTOS, SO ele ESI Ne Oe ROT NR ee RR ER A A ee ee 
