Table 3-1. Operator's Controls

TM 11-6625-537-14-1

Table 3-1. Operator's ControlsContinued

Control, indicator

Function

or connector

Used for connecting to the chassis of the electronic voltmeter. A 0.47 f

Chassis ground terminal

capacitor is connected from the middle input terminal to the chassis ground

terminal. Since the chassis of the electronic voltmeter is always connected to

ground through the third wire of the three-wire power cord, the external

circuit should be checked for conflicts in grounding before connecting the

middle input terminal to the chassis ground (bottom) terminal.

Applies ac line voltage to the primary of the power transformer.

ON switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

OPERATE-CALIBRATE control . . . . . . . . . . . . . .

Remains at the OPERATE position all times except when it is necessary to

calibrate the internal 500-volt dc reference supply. When hold at

CALIBRATE. a representative sample of the reference voltage is compared

to the voltage of an internal standard cell and any difference is indicated on

the VOLTS meter,

Varies the output of the 500-volt dc reference supply. When the OPERATE-

CALIBRATE control . . . . . . . . . . . . . . . . . . . . .

CALIBRATE switch is held at CALIBRATE, the reference supply is set

accurately by adjusting the CALIBRATE control for zero VOLTS meter

deflection,

a. Selects maximum input voltage ranges of 500, 50, 5, and 0.5 volts, and ac

RANGE control . . . . . . . . . . . . . . . . . . . . . . . .

null multipliers of x100, x10, x1, and x.1 to be used, respectively, with each

voltage range. Also selects the decimal point indicator lamps for each

setting.

b. When voltmeter is used as a dc vtvm (NULL switch is set to VTVM, AC-de

polarity switch set to + or ), the proper signal from a voltage divider is

connected to the meter circuit.

c. When the voltmeter is used as a differential dc voltmeter (NULL switch not

set to VTVM. AC-dc polarity switch set to + or -), the proper reference

voltage is selected.

d. When voltmeter is used as an ac vtvm (NULL switch is set to VTVM, AC-

dc polarity switch set to AC) the proper signal from a voltage divider is

connected to the meter circuit.

e. When voltmeter is used as an ac differential voltmeter (NULL switch not

set to VTVM, AC-de polarity switch set to AC), the proper AC NULL

MULT (null voltage multiplier) is selected.

NULL control . . . . . . . . . . . . . . . . . . . . . . .

a. Selects VTVM circuit or sensitivity of meter circuit.

b. VTVM connects the input voltage to the meter circuit through a voltage

divider selected by the RANGE switch.

c. 10, 1, .1 and .01 are used to perform differential voltage measurements and

connects to the meter circuit, to indicate the difference between the unknown

voltage and a known internal reference voltage indicated by the voltage

readout dials.

d. For differential dc voltage measurements, the NULL control positions

represent full scale differences between the unknown voltage and the known

internaI reference voltage indicated by the voltage readout dials.

e. For differential ac voltage measurements, the NULL control setting times

the AC NULL MULT indicated by the RANGE control, represents full scale

differences between the unknown voltage and the known internal reference

voltage indicated by the voltage readout dials.

A, B, C, D, and E voltage readout dials . . . . .

Select the amount of internal reference voltage necessary to null the unknown

voltage. These dials also provide an in-line readout of the reference voltage.

Indicator A has a range from 0 to 4; indicators B through D, a range from 0

to 9; and indicator E, a range from 0 to 10.

Serve as decimal points for the voltage readout dials. When the RANGE

Decimal point indicator lamps . . . . . . . . .

switch is set to 500, the indicator above dial D will light; when set to 50, the

indicator above dial C will light; when set to 5, the indicator above dial B

will light; when set to .5, the indicator above dial A will light.

AC-de polarity control . . . . . . . . . . . . . . . .

a. Selects the ac, + dc or -- dc mode of operation.

b. When set to AC, the unknown voltage is converted to an equivalent dc

voltage and applied to the voltage divider and meter circuits.

c. When set to +, the upper input binding post is positive with respect to the

common input binding post.

d. When set to +, the upper input binding post is negative with respect to

the common input binding post. The polarity of the known internal reference

voltage, and the polarity of the VOLTS meter are reversed, and an 88

megohm resistance is connected between the common input terminal and

chassis ground, when the AC-dc polarity switch is set to --.

3-3