Chapter 5— BATHYTHERMOGRAPH 



When shifting from one head to the other, the 

 recorder also indicates the difference in depth 

 between the two sound heads. 



6. The press-to-set 4800 fps switch is de- 

 pressed. When the drum rotates to a velocity 

 reading of 4800 fps, the switch is released. 

 The drum then will rotate and begin to give 

 a continuous record of velocity and depth for 

 the sound head in use. 



Checks and Adjustments 



Minimum front panel controls and adjusting 

 knobs are contained on the AN/BQH-lA. Peri- 

 odically, the operator should depress the press- 

 to-set switch and verify that the initial calibration 

 accuracy of the equipment is maintained through- 

 out an operating period. 



Emergency Use 



Because the velocity display and depth display 

 on the AN/BQH-IA are independent of each 

 other, the recorder is capable of emergency 

 operation on either independent channel. If failure 

 of the depth circuitry occurs, an operator may 

 continue to supply useful velocity information 

 by manually positioning the depth pen to a readable 

 portion of the chart. In the event of failure in 

 the sound heads or drum circuitry, depth informa- 

 tion may still be supplied independently. 



71.113 

 Table 5-1. — BT Series Designations 



Series No. 



OC-l/S j 

 OC-IA/S ' 

 OC-IB/S i 

 OC-IC/S ^ 



0C-2/S J 

 0C-2A/S ' 

 OC-2B/S 1 

 OC-2C/S 1 



OC-3/S 

 OC-3A/S 

 OC-3B/S I 

 0C-3C/S ' 



I 



Name 



Shallow 



Medium 



Deep 



Design depth 



to 200 feet 



to 450 feet 



to 900 feet 



SHIPBOARD BATHYTHERMOGRAPHS 



A surface ship is much less concerned with 

 buoyancy and salinity data than is the submarine, 

 consequently the shipboard BT is required to 

 make only temperature versus depth measure- 

 ments. Three types of mechanical BT are in 

 general use aboard ships. One type is used 

 for measuring shallow depths (200 feet), another 

 for medium depths (450 feet), and the third for 

 deep water (900 feet). The BT carries a coated 

 glass slide on which is scribed temperature 

 changes as the BT dives to its operating depth. 

 Upon retrieval, the temperatures are read by 

 placing the slide in a gridded viewer. Essentially, 

 each BT is constructed the same, and each one 

 operates in the same manner. Differences will 

 be noted where applicable. Table 5-1 lists the 

 various BTs in use and gives their designed 

 operating depth. A new type, the expendable BT, 

 is discussed later in the chapter. 



DESCRIPTION OF UNITS 



All three BT types use the same size slide 

 for recording temperature and depth. To elabo- 

 rate, the slide used in the deep model shows 

 4-1/2 times more data than the one used in the 

 shallow model. The information taken by the deep 

 BT is compressed, in compai'ison to the shallow 

 recording. Because of this compression, it shows 

 less detail and thereby makes it more difficult 

 to read accurately. Lowering a deep-type BT in 

 shallow water to obtain a recording is impractical 

 because insufficient detail is gleaned from the 

 slide to make accurate readings possible. 



The deep BT differs slightly from the other 

 two in that it does not have a stylus lifter. The 

 stylus lifter on the shallower BTs lifts the 

 stylus from the slide as the BT comes to within 

 70 to 50 feet of the surface while being retrieved. 

 This action prevents double traces that would 

 complicate the reading of surface temperature. 

 Another difference is that the spring on the 

 depth element is outside the bellows. Because 

 the deep BT pressure element is smaller (to 

 withstand the pressure of deep water), the spring 

 cannot fit inside the bellows as it does in the 

 depth elements of shallower BTs. Some old 

 models of the deep BT may further be identified 

 by a diving lug mounted just forward of the fin 

 guards. The diving lug allows for very deep- 

 angled dives to enable the BT to reach its 

 designed depth in a minimum amount of time. 

 Figure 5-2 shows a typical mechanical bathy- 

 thermograph. 



61 



