Page 517 echo sounding 



Table 19. — Index adjustments of Dorsey Fathometer No. 3. 



5543 



For the 1,000-fathom index adjustment, both the starting-frequency and the depth-selector 

 switches must be on position 5. By means of a temporary electric connection, a smaU amount of 

 energy from the 525-cycle oscillator should be introduced into the input of the sonic echo amplifier — • 

 the amplifier used by the 312 Fathometer system. Then the gain of the amplifier should be lowered 

 until only the transmitted signal caused by this coupling will be registered. Then the 1,000-fathom 

 scale index is adjusted to the same value to which the other indexes were adjusted. 



5543. 312 Fathometer 



The 312 Fathometer is provided with two adjustments by which the position of 

 the index may be altered. One of these adjustments is on the back of the index disk 

 inside the indicator cabinet. It is known as the draft adjustment. By means of it the 

 position of the slit, through which the flash of the neon tube is seen, may be changed 

 relative to the index disk on which it is located. The draf' should be compensated for 

 by this adjustment. The slit is in a movable segment of the disk. The wing nut 

 securing this segment must first be loosened so the segment can be moved by hand to the 

 desired setting as indicated by an engraved scale on the back of the index disk. Then 

 the wing nut should be re tightened. 



The other adjustment is to vary the time of the transmitted signal with reference 

 to the zero of the dial scale. By it the algebraic sum of the instrumental error and 

 settlement and squat should be compensated for. This adjustment is made by varying 

 the position of the dog which closes the electric contact. The dog is secured to the 

 disk by two set screws, which are loosened so the dog may be moved around the disk 

 to transmit the signal at the correct time with reference to the zero of the dial scale. 

 The set screws should then be retightened. 



For proper operation on the 100-fathom scale the contactor that operates the oscil- 

 lator should be held closed for a period of time equivalent to 1 to 3 fathoms, depending 

 on the installation. The contact surface of the dog is designed to accomplish this and 

 it is also provided with a beveled surface to allow for adjustment. The distance be- 

 tween the contact points may be varied by loosening the nut under the brush of the 

 contactor assembly and varying the adjustable stop which is a round disk having two 

 flattened segments on opposite sides. 



