9-26 Reading (he Strip Chart. — In reading 

 the voltage signals on tlie strip chart, some 

 variability of results will be inevitable from 

 person to person. The principal sources of this 

 variability arise in making estimates of the 

 average voltage due to the mean water current 

 through the confusion of turbulence and wave 

 signals, and making estimates of each turn 

 signal. Better results are obtained in deter- 

 mining the average voltage if done entirely by 

 eye without the use of pencil marks or a ruler. 

 Estimation of the beginning and end of a turn 

 signal can be aided by measuring the interval 

 of time during execution of a turn. Inasmuch 

 as the electrodes are towed at a considerable 

 distance behind the ship, there is a lag in the 

 electrode's turn signal. Thus the electrodes do 

 not steady on the new course for a minute or so 

 after the ship has steadied and similarly do not 

 commence their turn when the ship commences 

 turning. The turn signal lasts as long as the 

 ship's turning time and is received approxi- 

 mately LICs minutes after the ship has com- 

 menced turning. L is the length in meters of 

 the cable towed astern, and Cs is the ship's 

 speed in meters per second. Anticipating and 

 marking the beginning and ending of the turn 

 signals as they occur will improve the consist- 

 ency of interpretation of the data, both at sea 

 and in later study of the records. It is well to 

 be extravagant in delineating the turn signals, 

 for if the voltage shift on two courses is Targe, 

 both the electrodes and the capacitors in the 

 wave signal suppressor (filter resistance) must 

 have time to come to equilibrium. 



Best results are obtained if the first half of a 

 fix signal is viewed with suspicion and greatest 

 weight is given the latter portion of the trace 

 when the ship's heading, the electrochemical 

 system of the electrodes, and the capacitors in 

 the wave signal suppressor system have all had 

 time to come to equilibrium. Although instru- 

 ment zero lies in the center of the chart paper, 

 the electrode zero point does not necessarily 

 coincide with the instrument zero point, unless 

 adjusted bv the electric zero control. 



9-27 Securing the GEK After a Current 

 Fix. — After a current fix, the instrument is 

 secured by turning all switches on the panel 

 inside the instrument door to OFF {DOWN) 

 position (sec. 9-20). In addition, the cable 

 must be retrieved if the ship is to be stopped 

 before taking the next current fix. In the case 

 of a long cessation of operations, the AC power 

 supply should be unplugged from the recorder, 

 and the automatic current adjuster should be 

 taken out of the operating (standard cell) 

 position (sec. 9-20). 



9-28 MAINTENANCE OF THE GEK.— 



Both routine and special maintenance for the 

 recording unit are described in detail in the 

 direction manual supplied with the instrument. 



The parts of the recorder are easily acces- 

 sible. The door opens wide to the left. The 

 chart-drive -reroll unlatches to swing out to 

 the right, bringing the chart to a handy 

 position for replacement and exposing the 

 main slidewire. With or without the chart- 

 drive-reroU latched in place, the entire assembly 

 swings out around the same hinge making the 

 balancing motor, paper-drive motor, standard- 

 izer, and dry cell completely accessible. Am- 

 plifier, fuses, and terminal boards are then ex- 

 posed on the back of the recorder case. To 

 inspect the amplifier, remove the entire unit 

 from the case. A small indicator at the left 

 edge of the strip chart shows a red signal when 

 a new dry cell is needed. 



9-29 The Strip-Chart Paper,— A roll of 

 strip-chart paper is 120 feet long. It is driven 

 at a speed of )i inch per minute; consequently, 

 it should last for about 5 days of continuous 

 operation. Note how the roll in the instru- 

 ment is threaded through the guides so that the 

 fresh roll can be threaded properly when it 

 is necessary to change rolls. Sometimes the 

 paper on the take-up roll tends to bunch or 

 bind at one end. This can be straightened 

 by adjusting the thumb screw at the left end 

 of the feed roll until both edges of the paper 

 line up in the slot cut in the platen above the 

 telltale wheel at the right. Badly bunched 

 paper should be rerolled before adjusting the 

 thumbscrew. 



9-30 The Recorder Pen. — If the pen stops 

 inking while it still contains ink, moisten a 

 finger and draw it across the penpoint. If 

 this fails to start the flow of ink remove the 

 pen from the carriage, and push a fine wire 

 through the point to clean out any particle 

 clogging it. If the ink still does not flow, in- 

 stall a new pen. Place the clogged pen in 

 alcohol or boiling water for a short time. 

 Remove the pen from the solution, and insert 

 a cleaning wire as previously directed. Then 

 fill the pen with alcohol or warm water, and 

 blow the liquid out through the penpoint. 

 Allow the pen to dry thoroughly before using. 



9-31 Cable and Electrodes. — In case of 

 cable and/or electrode failure, the entire unit 

 of cable with electrodes must be replaced. 

 Inasmuch as the electrodes are matched and 

 balanced very carefully, any damage to one 

 electrode requires replacement of both. 



9-32 Junction Box. — The junction box, 

 where the cable plugs into the recorder line. 



H. O. 607 



91 



