INTRODUCTION TO SONAR 



71.72 

 Figure 5-2.— The bathythermograph. 



Except for the differences just noted, all 

 three of the BTs are constructed the same. 

 They consist of a thermal element, a depth 

 element, a body tube, a nosepiece, and a tail 

 guard. An auxiliary nose sleeve is available 

 to aid the BT in diving. These units are shown 

 in figure 5-3. 



Thermal Assembly 



The thermal assembly is the temperature- 

 measuring element. The temperature reading 

 represents the average temperature of the capil- 

 lary tube assembly, which is located in the tail. 



The tube assembly is wound in staggered fashion 

 on a six-sided frame that extends beyond the 

 body of the BT. This staggered winding ensures 

 a flow of water around the capillary tubing. 

 Breather holes in the body tube allow water to 

 run freely in or out, thereby keeping the internal 

 pressure equalized with the outside pressure. 

 The Bourdon tube element has a bimetallic 

 strip, and any difference in temperature between 

 the water within the BT surrounding the Bourdon 

 tube and the water flowing past the capillary 

 tubing is offset by the action of the bimetallic 

 compensator. 



NOSEPIECE 



NOSEPIECE 



PISTONHEAD 

 PISTON ^^\ .?Jr,'°l 



PEN BOURDON TUBE TAIL 



LIFTER / / 



HOLDER/' / _J \ 



© 



i 



PRESSURE 

 SPRING (STEEL) BELLOWS STYLUS STYLUS ARM 



PRESSURE UNIT THERMAL UNIT 



71.74 

 Figure 5-3.— The BT and its parts. 



62 



