TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
(3) Remember, voltages may appear unexpect-
13-1. Equipment maintenance.
edly in defective equipment. An open bleeder resis-
Accurate and appropriate test equipment is critical
tor may result in a capacitor retaining a dangerous
to the maintenance of electrical equipment. Listed
charge. Turn off power and discharge all capacitors
in table 13-1 are some of the tools and equipment
before connecting or disconnecting test leads to and
that each military facility electrical shop should
from the circuit being measured.
possess. A brief description of the equipment appli-
(4) For your own safety, inspect the test leads
cation is also given. To perform specialized testing,
for cracks, breaks or flaws in the insulation, prods
and connectors before each use. If any defects exist,
special equipment may be rented, or purchased de-
replace the test leads immediately.
pending upon projected future use. This testing may
(5) Do not make measurements in a circuit
be performed by experienced military facilities per-
where corona is present. Corona can be identified by
sonnel, or it may be contracted to an electrical test-
its sound, the odor of ozone or a pale-blue color
ing shop. In the sections that follow three of the
emanation from sharp metal points in the circuit.
more common and versatile test equipment avail-
(6) Hands, shoes, floor and workbench must be
able are described: the volt-ohm-miniammeter, the
dry. Avoid making measurements under humid,
damp, or other environmental conditions that could
in the use of all test equipment, these devices
affect the dielectric withstanding voltage of the test
leads or instrument.
should be used in strict compliance with the manu-
(7) For maximum safety, do not touch test
facturer's instructions and recommendations. Fail-
leads or instrument while power is applied to the
ure to do so may result in injury to personnel mak-
circuit being measured.
ing the tests as well as produce meaningless data.
(8) Use extreme caution when making mea-
13-2. Volt-ohm-milliammeter (VOM).
surements in a radio frequency (RF) circuit where a
dangerous combination of voltage could be present,
This meter incorporates the functions of the voltme-
such as in a modulated RF amplifier.
ter, ohmmeter and milliammeter into one instru-
ment. A VOM can be used to measure AC or DC
(9) DO not make measurements using test
leads which differ from those originally furnished
voltage, current and resistance, with several ranges
with the instrument.
for each function. There are also solid-state VOMS
(10) Do not come into contact with any object
which perform the same functions. For precise oper-
which could provide a current path to the common
ating procedures, the manufacturer's instructions
side of the circuit under test or power line ground.
must be referenced. A VOM which measures true
Always stand on a dry insulating surface capable of
RMS should be used.
withstanding the voltage being measured, or that
a. Safety precautions. A VOM is usually designed
could be encountered.
to prevent accidental shock to the operator when
(11) The range or function switch should only
properly used. However, careless use of the instru-
be changed when the power to the circuit under
ment can result in a serious or fatal accident. The
measurement is turned off. This will provide maxi-
VOM should only be used by personnel qualified to
mum safety to the user, eliminate arcing at the
recognize shock hazards and trained in the safety
switch contacts and prolong the life of the meter.
precautions required to avoid possible injury. Safety
b. Operation. Before making any measurements,
precautions are as follows:
the VOM pointer must be adjusted to zero. With the
(1) Do not work alone when making measure-
VOM in operating position, check that the pointer
ments of circuits where a shock hazard can exist.
indicates zero at the left side of the scale when there
Notify another person that you are, or intend to
is no input. If pointer is off zero, adjust the screw
make such measurements.
(2) Locate all voltage sources and accessible
located in the case below center of the dial. Use a
paths prior to making measurement connections.
small screwdriver to turn the screw slowly clock-
wise or counterclockwise until the pointer is exactly
Check that the equipment is properly grounded and
the right rating and type of fuse(s) are installed. Set
over the zero mark at the left side of the scale. With
the instrument to the proper range before power is
the indicating pointer set on the zero mark, reverse
the direction of rotation of the zero adjuster. Rotate