5266 HYDROGRAPHIC MANUAL PaGE 486 



5266. Operation 



The Dorsey Fathometer No. 3 is put into operation by the following procedure: 

 After starting 'the primary source of power, which may be either a steam turbogenerator 

 or a rotary converter, the starting-frequency switch on the front of the indicator 

 cabinet is turn^ed to position 2. Less than a minute is required for the vacuum tubes 

 to become sufficiently warm to operate, after which a 2050-cycle sound will be heard 

 in the indicator. Now the push button marked "motor starting," located directly 

 above the starting-frequency switch on the cabinet, is pressed to start the starting 

 motor, which drives the synchronous motor. Just before synchronous speed is reached 

 the starting switch is turned to position 3, which reduces the torque of the starting 

 motor, thus permitting synchronization to be accomplished more easily. 



A stroboscopic system has been incorporated in the indicating mechanism to aid in 

 synchronization. This consists of a neon tube, excited from the 1025-cycle source, the 

 intermittent light from which falls on the periphery of the synchronous-motor flywheel, 

 which contains 100 teeth. At synchronous speed the stroboscopic effect makes these 

 teeth appear stationary. The teeth may be viewed through a small window which is 

 just above the 20-fathom dial. Sufficient experience, however, will enable one to start 

 the synchronous motor by ear, without resorting to the stroboscopic method. The 

 synchronous motor will operate in some cases at a submultiple of synchronous speed, 

 and this possibility must be avoided by following the instructions in 5245. The speed 

 should be finally verified by counting the number of revolutions of the 1 ,000-f athom 

 index disk, which should revolve a trifle more than four times in 10 seconds (0.41 r. p. s. 

 to be exact). This check need be only approximate since an incorrect speed will always 

 be an even submultiple of correct speed. 



After the motor has been synchronized, the starting-frequency switch is turned to 

 position 4, if supersonic soundings in depths less than 300 fathoms are desired. In this 

 case the depth-selector switch is set on position 1, 2, 3, or 4, depending on the depth to 

 be sounded. If the depth exceeds the limit of the supersonic sounding range of the 

 instrument, the starting-frequency switch is placed on position 5 and the depth-selector 

 switch also on position 5, assuming that the instrument has been adjusted by setting the 

 indexes in accordance with 5542. 



