Differential Voltmeter Operation

TM 11-6625-2724-12

instrument is operated as a megohmmeter as

NOTE

On the 10 and 1 millivolt ac ranges, an

follows:

a. Place the ME-202C/U controls to the following

observed offset of 200 microvolt is normal,

positions:

This is the internal noise of the voltmeter,

(1) POWER switch to ON.

a n d will not affect the accuracy of

(2) RANGE switch to 10.

measurements above this level.

(3) NULL SENS switch to .01 (.001 if the R is

3-5. Differential Voltmeter Operation

greater than 1010).

Operate the voltmeter as an ac or dc differential

(4) MODE switch to +DC.

voltmeter as follows:

(5) Readout dials to 0.00 00.

a. Determine the approximate value of the

b. Connect the unknown resistance between the

measured voltage by performing the TVM mode

HI and LOW INPUT terminals. Use short isolated

measurements described in paragraph 3-4.

leads to prevent measuring the leakage resistance

b. Place the MODE switch to the respective

between the leads.

polarity observed on the TVM mode measurement

c. Rotate the readout dials to botain a meter

and set the readout dials to the TVM measurement

deflection of - 1 and use the formula given in d

value. If an ac measurement is being made, leave the

below to determine the value of the unknown

MODE switch in its AC position.

resistance.

c. Place the NULL SENS switch to successively

d. The unknown resistance is as follows:

high null sensitivity positions and adjust the readout

dials to obtain a center-zero meter indication.

3-6 Use of Shorting Link

The INPUT ground terminal is directly connected to

the chassis of the instrument to provide a convenient

Rx = Unknown resistance

connection to earth ground whenever the line cord is

Ero = Readout dial voltage

connected to line power. Whenever measurements of

voltages having a reference other than ground, but

Em = meter deflection in volts (pro-

not exceeding 500 volts, are performed, the shorting

portional to selected NULL SENS).

link between the LOW INPUT and ground terminal

must be removed or damage to the measurement

343. Operation Under Unusual Conditions

source, or the ME-202C/U, or both, may occur.

Paragraph 1-9 lists the environmental conditions

3-7. High Resistance Measurements

under which performance of the unit is specified.

The ME-202C/U can be used as a megohmmeter for

Operation or storage beyond those limits, or under

measurements of high resistances from 10 to 106

conditions of sand, salt spary, etc, is not recom-

mended.

megohms with a typical accuracy of ± 05%. The

3-4