TM 11-6625-298-14
(2) Connect the cable sheath to the GROUND
3-18. Locating Low Insulation
terminal.
a. General. The ohmmeter may be used to
(3) Turn the hand generator crank at
locate low cable insulation caused by moisture.
operating speed. Full generator voltage (500 volts)
Such a trouble can be burned in by applying high
is applied directly across the fault. The current
voltage directly across the fault. This breaks down
ballast resistors are not in the circuit and there
the insulation at the fault and permits the bare
will be no reading on the ohmmeter scale.
wires to make metallic contact. When a solid
ground or short circuit has developed, the fault can
be located with a Wheatstone bridge test set or by
When measurements have been completed,
using tone and an exploring coil.
disconnect all test leads from the ohmmeter and
b. Procedure. To burn in trouble using the ohm-
from the equipment being tested. Close the hinged
meter, proceed as follows:
cover; place the ohmmeter and leads in the
(1) Connect the wire under test to the
carrying case.
GUARD terminal of the ohmmeter.
Section III. OPERATION UNDER UNUSUAL CONDITIONS
3-20. General
The main problem when operating the ohmmeter in
When operating the ohmmeter in regions where
desert climates is to prevent dirt, dust, and sand
extreme cold, heat, humidity, moisture, or sand
from filtering into the equipment. Keep the
conditions prevail, special precautions must be
equipment in the carrying case with the lid closed
taken to keep the equipment in operating condition
and latched at all times when not in use, and cover
at all times. Paragraphs 3-21 through 3-23 contain
with canvas or other material.
instructions for minimizing the effect of these
unusual operating conditions.
The main difficulty encountered in the operation of
the ohmmeter in tropical climates is high relative
Because the ohmmeter is intended for both indoor
humidity. Although it is sealed against humidity,
and outdoor use, the equipment may be exposed to
moisture still will condense on the outside of the
extreme cold in actual operation as well as in
instrument case whenever its temperature becomes
storage and in transport. When operated at ex-
lower than the temperature of the air. Mositure
tremely low temperature, the hand generator crank
collecting between the binding posts lowers the
will not operate as easily as at normal room
resistance between them and will cause faulty
temperatures. The generator drive assembly parts
readings. Dry the case with a dry cloth before
may break. If the ohmmeter is operated in a warm
attempting to make teats with the equipment.
place after exposure to the cold, moisture will
Inspect the equipment frequently to keep it free
condense on the equipment until the equipment
from rust, corrosion, and fungus growth. Perform
reaches room temperature. This condition also
preventive maintenance operations (para 4-3)
arises when the equipment warms up during the
frequently to keep the unit as moisture-free as
day after a cold night. When the ohmmeter has
possible.
reached room temperature, dry it thoroughly.
Perform preventive maintenance operations (para
possible.
