These components were then packaged for field use by building water- 

 proof containers for the pressure sensor and the logic circuitry. These 

 containers were constructed out of PVC pipe and fitted with caps that 

 had "0" ring seals to prevent leaking at shallow depths. The pressure 

 sensor housing was equipped with a pliable diaphragm to make it sensitive 

 to the environment. Connections between the components of the instru- 

 ment were made by waterproof oceanic connectors. 



The pressure sensor, signal conditioning circuitry, and power supply 

 batteries were then mounted on a metal platform for field use. This 

 platform is a triangular piece of 1/2-inch-thick steel equipped with a 

 vertical shank for shackling to the recovery line. Figure B-2 shows this 

 assembly with the pressure sensor housing mounted vertically with the 

 sensor diaphragm down so it is adjacent to the bottom and the signal con- 

 ditioning circuitry in the horizontally mounted container. Power supply 

 batteries were also mounted on the platform and waterproofed with a 

 "paint-on" sealant. 



Testing of this version of the instrument in the ocean from the end of 

 Scripps Pier indicated a number of problems which caused erroneous meas- 

 urements. The most serious problem was the progressive drift due to 

 electronic instability. Other problems included leakage of the paint-on 

 sealant and excessive drain on the batteries used as a power supply to 

 the signal conditioning circuitry. At this point it became necessary to 

 redesign the instrument and to restructure its components in order to 

 improve its performance. 



REDESIGN AND CONSTRUCTION OF THE INSTRUMENT 

 JUNE 1973 - FEBRUARY 1974 



The failure of the recording depth gage to hold an accurate measure- 

 ment and to drift from a zero setting was found to be related to the 

 batteries used to power the signal conditioning circuitry. This could 

 only be overcome by redesigning the circuit and replacing the batteries 

 with a regulated power supply. Figure B-3 shows a schematic diagram for 

 the present signal conditioning circuit which uses a 1.4 -volt mercury 

 cell as a constant reference voltage for the power supply. Also, a 

 reset switch was installed in the circuit to facilitate making multiple 

 measurements. 



These changes required modification of the waterproof containers 

 and the physical configuration of the instrument. The second version of 

 the instrument required an enlarged signal conditioning package so that 

 it could accommodate larger batteries for the power supply. This is now 

 a PVC container 7 inches in diameter and 11 inches long. Figure B-4 

 shows the present physical configuration of the recording depth gage with 

 a large and a small diameter waterproof package mounted vertically on 

 the same steel frame that constitutes the sensing package. This instru- 

 ment was then successfully tested in the laboratory deep tank and from 

 Scripps Pier. 



99 



