530 



EXPLORATION GEOPHYSICS 

 Reels 



Many different types of reels are employed for handling the field 

 wires. For shallow investigations, the length of lines usually does not 

 exceed about five hundred feet, and it is often convenient to place all of 



Fig. 320. — Equipment for shallow resistivity measurements, a, potential and energizing reels, 

 mounted on common shaft; b, hand cranked commutator system and milliammeter; c, potentiometer; 

 d, tripod; e, battery box. 



the reels on a common stationary shaft and locate the shaft near the 

 instrument. (Figure 320.) The potential and energizing lines are then 

 carried out from this central reel system. This method, however, suffers 

 a disadvantage where long lines are necessary, due primarily to two 

 factors: (a) high inductive coupling between the potential and power 



circuits and (b) undue strain 

 on the lines as they are 

 dragged over the surface of the 

 ground. 



For deeper investigations, 

 it is advisable to employ sepa- 

 rate reels, preferably of the 

 hand type illustrated in Fig- 

 ure 321. These hand reels 

 hold from 1500 to 2000 feet 

 of 5/32-inch to 3/16-inch di- 

 ameter wire and weigh ap- 

 proximately 55 pounds when 

 ii^,. ;;.i. i:.|ui|,nicMt -ct Lip at end of potential loadcd. The flanges of the 



line, a, reel; b, portable field telephone and buzzer sig- It, A' f -f 1 8 



nal; c, stake marking traverse distance; rf, non-polari- rCCl naVC a Qiameter 01 lo 

 zing^ electrode. (Courtesy of International Geophysics, -^^^^^ ^^^ ^^^ ^^^^ ^^^^ ^q_ 



