SECTION III. Test Equipment

TM 5-4120-394-BD

SECTION III. Test Equipment

B-3.

Field Expedient Test Equipment.

General Information:

Sometimes, in the process of assessing the battlefield damage, it is necessary to make voltage and resistance

measurements to determine where the fault is. Standard test equipment (voltmeter, ohmmeter, SWR meter, etc.) should

be used whenever possible. If standard test equipment is not available, field expedient equipment can be fabricated using

parts commonly found on the vehicle and in the forward maintenance areas. The following paragraph provides fabrication

instructions for making a voltmeter, ohmmeter, and RF transmitter output tester.

NOTE

Accurate measurements are not available. These are Go-No-Go meters.

Making a Voltmeter.

A voltmeter can be made from a light bulb and

two pieces of wire. The pieces of wire can be

connected to the case and center terminal of the

bulb by means of solder, twisting, or simply

holding the wire ends against the bulb (see

illustration). The voltage rating of the bulb should

be close to the value of the expected voltage

being measured. For voltages in the 18 to 30 vdc

range, any light bulb on the driver's master

panel, driver's instrument panel, gunner's panel,

commander's panel, or gunner's primary sight

can be used. For voltages of 5 vdc or less a two-

battery cell flashlight bulb can be used. The

presence of voltage will cause the bulb to glow.

Polarity of dc voltage does not have to be

observed; even ac voltage can be measured.

Twist exposed wire ends together and apply

solder, if available, and solder. Touch to voltage

source when ready to make measurements.

B-3