Dc Voltage Measurements - HP 3438A Operating And Service Manual

Model 3438A
Section 111
To avoid possible damage to the Multimeter,
do not change the position of the Input
Selector switch while voltage is connected to
the front or rear input terminals.
3-13. VR (Volts/Ohms). The VR terminal (front or
rear panel) is the high terminal for ac and dc voltage
measurements. For ohms measurements, it is the positive
(+)
terminal.
3-14. COM (Common). The COM terminal is used for
all five Multimeter functions. It is the negative (-)
terminal for ohms measurements and it is the low
terminal for ac and dc voltage and current measurements.
The rear panel COM terminal is only used for voltage and
resistance measurements.
To avoid possible damage to the Multimeter
circuitry, the voltage between COM and
(earth ground) must not exceedplus or minus
500
V
dc.
3-1 5. A (Amps). The A terminal is the high terminal for
ac and dc amps measurements. There is a 2 amp input
protection fuse in series with this terminal.
The current function is protected by a fuse of
250 V rating. To avoid damage to the
Multimeter, current sources having open
circuit voltages greater than 250 V (dc +peak
ac) must not be connected to the A (aqps)
input terminal.
3-16. DC Voltage Measurements (Front or Rear
lnput Terminals).
To avoid possible damage to the Multimeter
circuitry, the dc input voltage must not exceed
I200 V (dc
+
peak ac).
3-1 7. Procedure.
a. Depress
- 7 -
V (dc volts).
b. Depress proper manual range (200 mV to 1200 V)
or depress AUTO for automatic range selection.
c. Connect test leads from the Multimeter V R (high)
and COM (low) terminals to the voltage under test as
shown in Figure 3-4.
Figure 3-4. DC Voltage Measurements.
3-18. A C Voltage Measurements (Front or
Rear lnput Terminals).
To avoidpossible damage to the Multimeter
circuitry, the ac input voltage must not exceed
1700 V (dc
+
peak ac).
3-19. Procedure.
a. Depress V (ac volts).
b. Depress proper manual range (200 mV to 1200 V)
or depress AUTO for automatic range selection.
c. Connect test leads from the Multimeter VR (high)
and COM (low) terminals to the voltage under test as
shown in Figure 3-5.
INPUT
v-n
n
N
COM
AC VOLTAGE
SOURCE
2 A FUSE
1
I I
Figure 3-5. AC Voltage Measurement.