Movement of the core in the differential transformer produces a 

 linear d.c. output voltage from the unit. This signal, representing the 

 wave conditions, is amplified and applied to a strip-chart recorder. 



2. Fabrication of a Pressure-Sensitive Gage 



Fabricate the pressure-sensitive underwater unit as outlined on 

 Figure 35. Table IX is a parts list for this gage. When soldering the 

 end caps to the bellows, ensure that a watertight seal is provided and 

 also prevent any solder from entering the corrugations of the bellows. 

 The end for the bellows which is drilled for the magnet should be soldered 

 to the bellows first. The magnet should then be inserted using an epoxy 

 cement to ensure that it remains in place. The threaded end for the 

 bellows is then assembled (soldered) using the minimum heat required for 

 soldering. Too much heat could lower the efficiency of the magnet. It is 

 recommended that edges of the bellows and the end caps be tinned prior to 

 soldering into an assembly. It is also recommended that liquid stainless 

 steel flux and solid wire solder, 60 percent tin and 40 percent lead, be 

 used. 



When assembling the bellows unit to the main gage housing, use of 

 Permatex No. 2 on threaded surfaces is recommended. The Permatex should 

 be used sparingly, applying only a thin coat on both the male and female 

 threaded parts. Prior to closing the space between the bellows and gage 

 housing, remove any excess Permatex from inside the "0" ring; align the 

 brass ring, which incloses the "0" ring, with the outside gage housing 

 and tighten the housing firmly. Do not use the bellows as a purchase 

 grip to tighten the assembly; vise grip pliers and a bench vise are 

 recommended. 



The bellows should be assembled to the gage case, and the entire case 

 and bellows tested for leaks prior to further assembly. This can be done 

 by attaching a fitting to the cable end of the gage housing, filling the 

 inside with air to about 30 pounds per square inch gage, and testing under 

 water for bubbles. During this test, the bellows snould be blocked mechan- 

 ically to prevent stress beyond its ratings. Blocking may be accomplished 

 by using large plastic washers with small holes in their edges for accept- 

 ing wire to hold the bellows in a blocked position. The washer used on 

 the threaded end of the bellows will require a slot with an opening in 

 order to place it above the bellows cap as shown in Figure 36. 



After testing the bellows and housing assembly, a short length of 

 gage cable is fitted into the end of the gage housing and sealed with 

 epoxy resin. Splicing the cable ends to a very fine flexible wire in the 

 epoxy seal will aid later assembly of the transducer. Clean, but do not 

 oil, the sliding core in the Sanborn linear differential transformer. 

 Clean the core and center hole thoroughly. If the core does not slide 

 freely in the transformer, return the transformer and core to the manu- 

 facturer for repair or replacement. Any binding of the core will cause 

 it to separate the steel ball from the magnet and render the gage useless. 

 The steel ball and magnet provide a backlash-free universal joint that 

 allows free movement of the core within the transformer. The core 



64 



