78 



HYDROGRAPHIC MANUAL 



fers a five-minute time interval. This time 

 interval is controlled by a fixed cam set at 

 the factory. The precision of the time inter- 

 vals is very hig-h as the cam is controlled by 

 the same synchronous motor used to drive 

 the scanning- mechanism. One roll of paper 

 will last about a week on 24-hour operation. 



3-82 Checking accuracy of PDR timing 

 circuits and mechanism. — ^The most common 

 check made on the operation of PDR equip- 

 ment is to record time ticks from WWV 

 directly on the graphic record. To make 

 this check the WWV signal from radio is 

 fed directly into the PDR headphone jack 

 and a record made for a period of several 

 minutes. This can be done without much 

 interference with the soundings and it is 

 common practice to make such a recording 

 once each four-hours watch. If the speed 

 of the stylus is correct (400 fathoms per 

 second) the WWV ticks will fall one under 

 the other and the leading edge of the ticks 

 will be nearly parallel to the twenty-fathom 

 markers. By making recordings several 

 hours apart, it can be determined whether 

 the PDR is running fast or slow and 

 the precision of the timing function ascer- 

 tained. If the WWV ticks appear to move 

 to the left about 8 fathoms over a pe- 

 riod of four hours continuous operation 

 then the PDR is running a little fast and 

 the error is one part in 720,000. Should the 

 movement be to the right the PDR would 

 be running slow. A word of caution: The 

 adjustment of the precision fork which con- 

 trols this accuracy is not a normal field 

 adjustment and should not be attempted un- 

 less proper equipment is on hand to insure 

 accurate results. 



The main reason for making this check 

 is to be sure the synchronous drive system 

 is operating at synchronous speed. Faulty 

 soundings will result if the scanning mech- 

 anism is operated at other than 400 fathoms 

 per second. 



3-83 Identification of 400-fathom phas- 

 ing. — The PDR graphic record is contin- 

 uous and the changes in phase are auto- 

 matic. Thus the value of the baseline must 



be known at all times as it can be any multi- 

 ple of 400 fathoms. The value of the baseline 

 is denoted by such an expression as plus, 

 400 plus, 800 plus, 1,200 plus, etc. At every 

 change of phase the value for the baseline 

 should be entered on the graphic record. 

 When the phase remains constant, the value 

 of the baseline should be recorded at inter- 

 vals of 30 minutes. 



Methods for determining the absolute 

 value of the baseline vary depending on the 

 equipment available. The most common 

 method is to switch back to the EDO-185 

 and record a few soundings on the 6,000- 

 fathom scale. Most installations permit this 

 to be done. Where it is feasible, a second 

 EDO-185 can be turned on for brief intervals 

 or another sonar sounding set operating at a 

 different frequency can be used to give this 

 information. When conditions are favor- 

 able, it is possible to check the phase by 

 listening on a pair of headphones and count- 

 ing the number of seconds between the trans- 

 mission and reception of the last ping of a 

 group. The slow drum recorder equipment 

 mentioned in the PDR instruction book is 

 not available. 



3-84 EDO-255 Depth Recorder.— The 



EDO-255 Depth Recorder, Model C (Fig. 

 26) was developed jointly by the EDO Cor- 

 poration and the Electronics Laboratory of 

 the Coast and Geodetic Survey to comply with 

 requirements and specifications agreed on by 

 various agencies interested in the project. 



The instrument is a portable, supersonic, 

 graphic recording, echo sounder, designed 

 for accurate hydrographic surveys in shallow 

 to moderately deep water by vessels of any 

 size. 



Its range is from about 2'/j feet below the 

 transducer to 230 fathoms. All electrical 

 components except the transducer, are housed 

 in a compact, sturdy, weather-proof cast- 

 aluminum cabinet. The recorder will operate 

 in any position. 



The principal characteristics of the EDO- 

 255 are: 



(a) It is designed to operate from a 110- 

 115 volt, single phase power source with a 

 frequency range of about 57.5 to 62.5 cycles. 



