Page 459 echo sounding 5216 



oscillator and hydrophone below the surface of the water. Wlien the 100-fathom scale 

 is used in sounding, the neon tube for that scale rotates at 4.1 r.p.s. This neon tube 

 is electrically connected through a switch to the output of the gas discharge tube. When 

 a change is made from one speed to the other, the gearshift mechanism, in addition to 

 changing the speed of the index disk, switches the gas discharge tube circuit from one 

 neon tube to the other. 



Signals are normally sent once each revolution of the index by closing the electric 

 circuit through the 525-cycle generator and the 1050-cycle oscillator. This is done by 

 means of a dog mounted on the shaft which rotates the index disk. The dog is adjust- 

 able circumferentially so that the time of starting the signal may be controlled. 



Echoes received on the 100-fathom scale near 100 fathoms (which is also the zero 

 of the scale) are difficult to distinguish from the transmitted signals. By transmitting 

 a signal only every alternate revolution this difficulty is overcome, and the echo and 

 transmitted signal are seen alternately. The circuit by which every alternate signal 

 is deleted is called the 100-fathom cutout. It consists of a wheel that rotates at half the 

 speed of the disk, which has metal and insulating segments so arranged that the brushes 

 which contact it complete an electric circuit once every alternate revolution of the disk. 

 The keying contactors and the 100-fathom cutout circuit are electrically connected in 

 series so that current can flow through the series combination only once each alternate 

 revolution of the disk. The 100-fathom cutout is switched into or out of operation by 

 means of a toggle switch on the underside of the cabinet. A cutout on the right side 

 of the cabinet may be operated manually for the same purpose. This latter cutout is 

 utilized when depths of 200 or multiples thereof are received on the 100-fathom scale. 

 And it may be used with both the 100- and 600-fathom scales. 



5216. Operation 



To operate the 312 Fathometer for sounding, the starting switch is closed, and a 

 period of a few seconds is allowed for the motor to come to operating speed. By the 

 frequency-control rheostat the frequency is adjusted to 525 cycles, or some value near 

 this which has been found to give optimum results. The hydrophone current is then 

 adjusted by means of the right-hand knob, so that it is from 1 to 5 milliamperes. The 

 gain control of the amplifier is adjusted for optimum operation (see 5163). The motor 

 speed should be adjusted so that the middle reed of the tachometer is vibrating at 

 maximum amplitude. The instrument is now ready for sounding on the scale selected 

 in accordance with the depth of the water. 



522. Simplex-Bludworth 



The Simplex-Bludworth Fathometer, Model ES-\04:, is manufactured by National 

 Simplex-Bludworth, Incorporated, of New York City. It is a semiportable, supersonic, 

 graphic-recording, echo-sounding instrument designed for surveys in shallow to moder- 

 ately deep water and for temporary installation in a launch or vessel. It is an instru- 

 ment of the same general type as the 808 Fathometer and is similar to it in many 

 respects (see 523). This is the most recently acquired echo-sounding instrument of 

 the Coast and Geodetic Survey and has not yet been tested in the field. It is only 

 briefly described here, mainly for the purpose of pointing out those features that dis- 

 tinguish it from the 808 Fathometer. The fact should be noted that it was not avail- 

 able when other parts of chapter 5 of this Manual were written. 



