Observation of Excursions of Voltage about a Nominal Value

TM 11-6625 -537-14-1

single frequency. When adjusting the voltage

given value such as the variations in the output

voltage of a dc power supply. Perform initial

readout dials, VOLTS meter needle deflection to

operation in accordance with paragraph 3-5 and

the right indicates that the unknown voltage is

proceed with the following steps:

greater than the internal voltage and the voltage

(1) Set AC-de polarity switch to desired

readout dials should be increased. The voltage

position corresponding to voltage to be measured.

readout dials should be decreased if the VOLTS

meter needle deflects to the left.

(2) Connect voltage to be monitored to input

(1) Perform initial operation in accordance

terminals. Always connect grounded side of input

(2) Set AC-de polarity switch to AC.

to lower input terminal.

(3) Connect unknown ac voltage to input

(3) Set RAN GE control to lowest position

terminals. Connect grounded side of input to

t h a t w i l l a l l o w a n o n s c a l e VOLTS meter

lower input terminal (middle terminal).

deflection. Note approximate value of voltage to

be monitored as indicated on upper VOLTS meter

(4) Set RANGE switch to lowest position

scale. When monitoring a dc voltage, set AC-de

that will allow an on-scale VOLTS meter

polarity switch to + (positive) or (negative) as

deflection. Note approximate value of unknown

to obtain VOLTS meter needle

required,

v o l t a g e as indicated on upper VOLTS meter

deflection to the right.

scale.

(4) Set voltage readout dials to correspond

(5) Set voltage readout dials A and B to

to approximate value of voltage to be observed.

correspond with the approximate value deter-

mined in (4) above, and set dials C, D, and E to O.

(5) Set NULL control to lowest position that

will allow voltage excursions to remain on scale.

Examples:

A B (RANGE switch

Voltage

492 Vac

500

(6) Read voltage excursions from lower scale

500

155 \'ac

of VOLTS meter. When monitoring dc voltages,

500

65 Vac

full scale right and left VOLTS meter deflections

35 Vac

are equal to the setting of the NULL control.

2.1 Vac

0.125 Vac

When monitoring ac voltages, full scale right and

left VOLTS meter deflections are equal to the

NOTE

setting of the NULL control multiplied by the AC

Set voltage readout dials slightly below

NULL MULT indicated by RANGE control

t h e appropriate value as indicated in

setting, Full scale ac deflections for recommended

the example.

settings of the RANGE and NULL control are

(6) Set NULL switch to 10.

shown in figure 3-3. Voltage under observation

(7) Advance voltage readout dial B until

has increased when VOLTS meter deflects to

VOLTS meter needle deflects to left and then

right, and decreased when VOLTS meter deflects

back one stop to return needle to right side.

to left.

(8) Set NULL switch to each succeeding

Example: With the electronic voltmeter con-

lower position, adjusting voltage readout dials C

nected to a 450 volts dc power supply, and set U P

through E as required to maintain zero VOLTS

t o observe voltage excursions, the following

meter needle deflection until the desired accuracy

indications were observed:

is obtained. Refer to table 1-3 for recommended

settings to be used.

RANGE control set at 500

NULL control set at 10

(9) Determine accurate reading from voltage

Voltage readout dials set at 4,4, 5, 5, 0

readout dials; be sure to note location of decimal

VOLTS meter needle (varying) .2-O

indication.

This would indicate that the actual output of the

Examples: Voltage readout dials A, B, C, D, and

dc power supply being observed was 445.5 volts

E indicate 3, 8, 6, 5, and 9, respectively. If the

RANGE switch was on 500, the decimal indicator

dc. The excursions about the nominal were 2

volts dc which meant that the output voltage

between C and D would be illuminated and the

varied from 445.5 to 443.5 volts dc. This in-

voltage measured would be 386.59 volts ac. If the

formation would be used to determine that the

RANGE switch was on 5 and the decimal in-

output was stable within 0.5 percent.

dicator between A and B illuminated, the voltage

(7) Set NULL control to VTVM and

measured would be 3.8659 volts dc.

disconnect voltage from input terminals.

( 1 0 ) Set NULL switch to VTVM

and

f. Recording Voltage Excursions about a

disconnect voltage from input terminals.

e. Observation of Excursions of Voltage about

Nominal Value. Provisions to connect a recorder

to the electronic voltmeter are included on the

a Nominal Value. The electronic voltmeter can be

rear panel. If a recorder is to be used to record

used to observe excursions of a voltage about a

3-8