54 



HYDROGRAPHIC MANUAL 



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Figure 13. — Electronic Position Indicator Equipment; shore station on left, ship station on right. 



tances corrected. Random errors are not 

 predictable and cannot be compensated. At 

 the ship station they may be caused by : 



(a) Misalignment of local and distance 

 pulses. 



(b) Careless reading of the distance ver- 

 nier and dials. 



(c) Poor alignment of pulses due to in- 

 correct gain settings. ^ — 



At the shore station, they may be caused by : 



(a) Poor synchronization at the time of 

 the fix. 



(b) Incorrect setting of the balanced gain. 



The radial accuracy of a measured dis- 

 tance to a ground station is about plus or 

 minus 100 meters. The position accuracy de- 

 pends on the summation of the above errors 

 and the angle of intersection of the distance 

 arcs. The EPI system does not provide con- 

 trol suitable for plotting hydrography on 

 scales larger than 1 : 100,000 (see l-19b). 



3-27 Locating the shipboard equipment 

 and antenna. — From electrical considera- 

 tions, the controller-indicator and transmit- 

 ter should always be located where a good 

 welded ground connection can be made to 

 the ship's metal bulkhead or deck. Heavy 

 copper braid should be run from a metal 

 bulkhead or deck connection to the con- 

 troller-indicator and connected to the chassis 



in the vicinity of the antenna cable input 

 jack. A good ground here is very important 

 since it will determine the maximum range 

 of the instrument. The transmitter chassis 

 must be well-grounded to a bulkhead or 

 deck. 



The controller-indicator and transmitter 

 must always be separated by a minimum 

 distance of 10 feet. The choice of position 

 for the controller-indicator is most often 

 controlled by the space that is available in 

 the vicinity of the plotting table. When the 

 controller-indicator is located near the plot- 

 ting table, the hydrographer can supervise 

 its operation. It also simplifies communica- 

 tion between the various points of opera- 

 tion. When the controller-indicator is re- 

 motely located, a communication system 

 between this unit and the plotting room will 

 be needed. Two or three feet of space all 

 around the controller-indicator for operation 

 and maintenance of this instrument is de- 

 sirable. If the ship's power system is poorly 

 regulated, a voltage regulator should be used. 



In locating a shipboard antenna it is de- 

 sirable to get as much vertical component in 

 the antenna as possible. This is usually dif- 

 ficult as any wire supported vertically would 

 be too close to a supporting mast and cause 

 severe directional effects. The ideal practical 



