Description of Operating Modes

TM 11-6625 -537-14-1

5-2. Description of Operating Modes

switch S3 connect null and range divider R305

through R310 and the O- to 500-volt dc reference

a. Dc Measurements (fig. 5-2).

to the input terminals. Levels D and C of AC-de

(1) Dc vtvm mode. The electronic voltmeter

polarity switch S5 control the polarity of the O- to

operates in the dc vtvm mode when the NULL

500-volt dc reference to be in opposition to the

switch is set to VTVM and the AC-de polarity

input volt age, The difference between the input

switch is set to + (positive) or -- (negative).

voltage and the O- to 500-volt dc reference is

Levels B and C of NULL switch S3 connect null

developed across the null and range divider.

and range divider R301 through R310 to the input

NULL switch S3A applies the output of the null

t e r m i n a l s . The output of the null and range

and range divider to the dc vtvm where the

divider is 0.010 volt when a voltage corresponding

difference between the unknown voltage and the

to the RANGE switch setting is applied to the

O- to 500-volt dc reference is displayed on the

input terminals. RANGE switch S2C applies the

VOLTS meter. Full scale deflection of the VOLTS

output of the null and range divider to the dc

meter corresponds to the setting of the NULL

vtvm where the value of the unknown voltage is

switch. Levels A and B of AC-de polarity switch

indicated directly on the VOLTS meter, Full scale

S5 control the polarity of the VOLTS meter, The

deflection of the VOLTS meter corresponds to the

meter needle will deflect to the right when the

setting of the RANGE switch. The VOLTS meter

input voltage is greater than the O- to 500-volt dc

will deflect to the right if the polarity of the

reference. The unknown voltage is measured by

voltage at the input terminals is as indicated by

adjusting the value of the O- to 500-volt dc

the AC-de polarity switch, VOLTS meter MI is a

reference until the VOLTS meter indicates zero

zero center meter. Therefore, the setting of the

deflection. The unknown voltage is then equal to

AC-de polarity switch is not critical in the dc

the reference voltage indicated on the front panel

vtvm mode. Levels A and B of AC-de polarity

voltage readout dials. Capacitor Cl is connected

switch S5, are used to reverse the polarity of

between the common input terminal and chassis

VOLTS meter M I to obtain meter deflection to

ground to bypass eddy currents from the power

the right before proceeding to the dc differential

transformer. Level E of AC-de polarity switch S5

mode of operation.

connects 88 megohms resistance in parallel with

(2) Dc differential mode. The electronic

C 1 when differentially measuring negative dc

voltmeter operates in the dc differential mode

voltages to prevent charge accumulation on Cl

when the NULL switch is set to 10, 1, .1, or .01,

from affecting accuracy.

and the AC-de polarity switch is set to +

(positive) or (negative). Levels B and C of null

5-2