80 



HYDROGRAPHIC MANUAL 



(g) Soundings are recorded on an electro- 

 sensitive paper, without a carbon core or 

 aluminized backing, made by the Timefax 

 Corporation. The surface is a lighter grey 

 than the Teledeltos paper, it does not smudge 

 as easily, and is dust free. There are four 

 printed scales: to 65, 55 to 120, 110 to 175, 

 and 165 to 230. 



(h) Recording is accomplished by a stylus 

 mounted on an endless rubber belt. As the 

 recording stylus travels across the paper, it 

 makes contact with a trolley rail which 

 serves to transfer the signal from the re- 

 ceiver to the stylus and also acts as a guide to 

 assure straight line recording. A keying 

 brush extending upward is also attached to 

 the belt and is guided by a groove in the 

 plate above it. This brush makes contact 

 at one of four adjustable keying contacts 

 as selected by the phase switch. It should 

 be noted that the keying brush and the stylus 

 are similar in construction and method of 

 attachment to the belt. The keying brush 

 does not key the EDO-255 transmitter di- 

 rectly. This function is accomplished by a 

 multivibrator circuit which is triggered by 

 the keying brush on the belt. 



(i) The paper is drawn across the platen 

 at a rate of one or two inches per minute 

 by one of two paper drive motors. The se- 

 lection of paper speed is made by means of 

 a switch on the control panel. 



(j) One barium titanate transducer (see 

 3-104) operating at a frequency of 37.5 kc 

 is used to produce the sound wave and receive 

 the echo. The transducer furnished is equip- 

 ped with an impedance matched cable which 

 is part of the electrical circuit. This cable 

 must not be cut. 



3-85 Calibrated velocity and variable 

 frequency. — The EDO-255 is designed so that 

 the frequency of the power supply can be 

 varied to accommodate changes in the veloc- 

 ity of sound in sea water through a range of 

 about 4,600 to 5,000 feet (767 to 833 fath- 

 oms) per second. It is possible to vary the 

 frequency over a range of 57.5 to 62.5 cycles, 

 thus decreasing or increasing the calibrated 

 velocity of 4,800 feet per second at 60 cycles. 

 The mean velocity of sound in the water 



area must be determined by velocimeter ob- 

 servations or by serial temperature and 

 salinity observations and computations. The 

 frequency can then be adopted which will 

 compensate for a variation from the standard 

 4,800 feet at 60 cycles, thus avoiding the 

 necessity of applying velocity corrections to 

 recorded soundings (see 5-120). A change 

 of 0.1 cycle will change the calibrated veloc- 

 ity 8.0 feet, thus if the velocity of sound in 

 sea water is determined to be 4,830 feet per 

 second, the frequency should be se*, and main- 

 tained at 60.4 cycles. The echo sounder op- 

 erator must continually monitor the fre- 

 quency and make any adjustment necessary 

 to hold it as nearly constant as possible (see 

 5-55). It should be remembered that a varia- 

 tion of 0.3 cycle represents a change of 0.5 

 percent in the soundings. 



3-86 EDO-255 phase adjustment.— Each 



successive scale or phase must be properly 

 correlated with the next shoaler one, that is, 

 a bottom echo at 60 feet on the first phase 

 should appear at 60 feet on the second phase, 

 etc. If the soundings do not agree, the keying 

 contact must be adjusted to bring the two 

 into agreement. This test and adjustment 

 can be made only in the feet mode. To make 

 the adjustment, set the fathoms calibration 

 switch to the ON position, the phasing 

 switch to 0-65, and function switch to slow. 

 Turn the draft adjustment so that the zero 

 depth mark (initial) is moved down to read 

 55 feet. Switch to the B scale (55-120) and 

 the mark should appear at 55 feet. If not, 

 the number 2 contact must be adjusted until 

 the stylus mark appears at 55 feet. Switch 

 back to the A scale (0-65) and the mark 

 should again appear at 55 feet. The C and 

 D scales can be similarly correlated. These 

 adjustments should be made by a qualified 

 technician. 



Since the initial appears only on the first 

 phase, the operator should check the initial 

 setting periodically when the recorder is be- 

 ing operated continuously on other phases. 

 This check can best be done when the vessel 

 is turning about between lines. 



3-87 Feet or fathom mode.— The EDO- 



