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MECHANICAL AND ACOUSTICAL SENSES 



necessarily minimum weight), it has the disadvantage of making further cir- 

 cuit adjustment difficult or impossible. Potting, therefore, seems most ap- 

 plicable for expendable USTs with relatively simple, reliable circuits. Many 

 commercially available USTs are of this type. 



Oil filling— -The transmitter components can be housed in a relatively 

 thin-walled plastic tube with rubber end caps and a filling of nonconductive 

 oil, e.g., dehydrated castor oil. The compliant end caps allow pressure equali- 

 zation between outside and inside, thereby permitting internal placement of 

 the pressure sensor. The remaining components must also be able to with- 

 stand pressure. The main advantage of this method is simplicity; there is no 

 need for a pressure-sealed housing. The primary disadvantages are greater 



Figure 10 Mark V hybridized transmitter (no sensors) packaged in an air-filled, O-ring 

 sealed housing. Right: Sealed battery module. Left: Plain end cap (in place of sensor 

 module). Center: Circuit module plugged into transformer/PST assembly (before the 

 latter potted into central tube). 



