HP 740B Operating And Service Manual page 23

Section ill
3-55. VOLTMETER.
3-56. DESCRIPTION.
3-57. In the Voltmeter mode, the Model 740Bfunctions
as a high impedance dc voltmeter with end scale
ranges from 1 MV to 1000 V. Ranges below 10mVare
obtai ned by using the SENSITIVITY pushbuttons to
increase meter sensitivity. The input voltage is in-
dicated on the meter.
3-58. OPERATING PROCEDURE.
3-59. The following steps describe the procedure for
using the Model 740B in the Voltmeter mode:
a. Set rear panel LINE VOLTAGE switch to cor-
rect position for available line voltage.
b. Connect ac power cord to ac power connector;
connect cord plug to ac line.
c. Turn on the Model 740B by depressing the
POWER pushbutton (indicator glows).
d. Set FUNCTION to VM.
- - - - - N O T E - - - - -
Digital readout tubes will not glow
in
VM
mode.
e. Check OUTPUT indicator. If glowing, de-
press to turn output off.
f. Connect input cable assembly (-hp- 110 54A)
to INPUT receptacle. Set INPUT Z switch
to
co •
g. Set RANGE and SENSITIVITY for the desired
end scale voltage (Table 3 -4).
- - - - - N O T E - - - - -
An additionalend scale voltage
range of 0.1 MV could be ob-
tained by setting RANGE to
1 m V and depressing X10 4 SEN -
SITIVITY. Meaningful mea-
surements cannot, however, be
made on this range due to the
problems of noise at this ex-
tremely low voltage level.
Model 740B
Table 3-4.
VM
Mode RANGE and
SENSITIVITY Settings
Desired End Scale
RANGE
SENSITIVITY
Voltage Range
1000 V 1000 V Xl
100
V 100
V Xl
10 V 10
V Xl
1
V
1
V
Xl
100mV
100 mV Xl
10mV 10 mV
Xl
1mV 10 mV
X10
100 MV 10mV
X10 2
10 MV 10mV
X 10 3
1 MV 10mV
X10 4
h. Zero the 740B input (1 mV range and below)
by connecting a shorting wire from + to -
INPUT terminals and adjusting ZERO control
for zero meter deflection.
i. Connect input box terminals for the type of
measurement desired using the information
in Table 3-5.
- - - - - N O T E - - - - -
Negative voltages upto 1 V canbe
measured in VM mode without re-
versing the + and - INPUT terminal
connections.
j. Read the input voltage on the 740B meter.
THE 740B INPUT SHOULD BE
DISCHARGED FOLLOWING ALL
HIGH VOLTAGE MEASUREMENTS
TO PREVENT CARRYING THE
STORED CHARGE TO THE NEXT
POINT OF MEASUREMENT.
k. Remove leads from device under test or de-
energize voltage source and place INPUT Z
switch to
2
MEG position to discharge 740B
input.
Table 3-5. Input Terminal Connections
TYPE
CONNECT INPUT TERMINALS
OF
MEASUREMENT
+
-
GUARD
~
Unguarded
To high (most To low (most To - Not
(floating) positive) of negative) of terminal Connected
source source
Guarded To high (most To low (most To reference Not
(floating) positive) of negative) of potential of Connected
source source
source
3-12 01794-1