TM 5-3820-256-10
(6)
Current switch. ON/OFF switch, located directly below the function switch. It is a momentary spring-return
toggle switch that turns on the electrical current to take resistivity measurements. The spring-return feature
prevents leaving on the current and subsequent battery drainage.
(7)
Cal adjust. Located in the lower right hand corner of the panel; used to zero the galvanometer when
calibrating the instrument.
(8)
Ohmmeter Potentiometer. Located directly above "cal adjust," it reads the earth resistivity directly in ohm-
feet. Select a position on the electrode selector switch and interpret the readings as follows:
Electrode selector
One division
Full scale
switch position
equals:
equals:
.25 ft NORMAL
1 ohm-feet
1000 ohm-feet-
2.5 ft NORMAL
10 ohm-feet
10,000 ohm-feet
10 ft NORMAL
40 ohm-feet
40,000 ohm-feet
(9)
Electrode selector switch. Five position switch located directly above the ohmmeter. On the right side, it
makes circuit connections for either the 0.25 or 2.5 ft NORMAL arrangement, as marked. When the switch
points straight up, the connections are for 10 ft NORMAL. On the left side, the connections are the 0.25 and
2.5 ft LATERAL arrangement, as marked. In the LATERAL arrangements, the 10 ft electrode serves as the
reference in both cases.
(10) Cable jack. The cable jack is the four-pronged receptacle (furnished with a dust cover) located in the upper
right corner of the panel. The jumper cable from the logger cable case is plugged in here, thus connecting
the instrument to the well probe.
(11) POT receptacle. Black plug receptacle for connecting the surface potential ground lead (lead-oxide flag)
wire to the instrument.
(12) CUR receptacle. Red plug receptacle for connecting the surface current ground (steel stake) wire to the
instrument.
d. Power Supply. The instrument requires three voltages: 1-1/2 volt ("C" cell battery), 9 volts (9 volt battery), and
45 volts (5, 9-volt batteries in series).
(Refer to figure 2-42.)
e. Test Set. The test set provides a means for checking the instrument operation and battery condition without
using the logging cable. It is normally kept in the base of the instrument. To use it: plug it into the cable jack;
plug the single red plug into the CUR receptacle and plug the black plug into the POT receptacle. Then follow
the usual logging procedure. You will, or course, have little, or no, "SP." The electrode selector switch may be in
any of the NORMAL logging positions.
f. Logging Cable. The cable used to lower the probe has four conductors covered with a durable 60% natural
rubber jacket. The cable is marked at five-foot intervals with numbered markers.
2-99
