3. EQUIPMENT AND INSTRUMENTS 



79 



Figure 26. — EDO 255-C, shoal water echo sounder. 



For portable installations a rotary converter 

 or inverter with variable frequency control 

 may be used with power derived from a 

 well-regulated 12-volt D.C. source or a 12- 

 volt battery. 



(b) A synchronous stylus drive motor as- 

 sures correct stylus speed when the motor is 

 powered by a supply source of dependable 

 frequency. A frequency meter graduated to 

 1/10 cycle is mounted on the control panel 

 where it can be constantly monitored and 

 the converter adjusted to maintain the de- 

 sired frequency. 



(c) The depth recording is linear. This 

 facilitates reading the fathogram and sub- 

 stantially reduces stylus and paper adjust- 

 ment errors. 



(d) The instrument will record depths 

 from 21/. to 230 feet, or about 1 to 230 

 fathoms in four phases of 65 units each and 

 having an overlap of 10 units. The phase 



shift is accomplished by a switch on the 

 control panel. Phase comparisons and adjust- 

 ments can be made on the bench. The 

 adjustment for each phase is made by shift- 

 ing the phase contacts slightly to reduce the 

 phase error to zero (see 3-86) . 



(e) The instrument is capable of record- 

 ing in units of feet or fathoms, however, 

 the operator cannot shift from one mode to 

 the other at will. The stylus motor is con- 

 nected directly to the drive pulley. In order 

 to change from feet to fathoms, or vice versa, 

 it is necessary to reposition the motor, an 

 operation requiring about 30 to 45 minutes 

 (see 3-87). 



(f) The position of the initial mark on the 

 fathogram is adjusted by the draft control 

 knob on the control panel. The initial 

 should not be set until the recorder has been 

 in operation at least 15 minutes. The initial 

 is recorded on the first phase only. 



