Ac Normal-Mode Rejection Test - HP 3438A Operating And Service Manual

Model 3438A Section
I V
MULTIMETER
BOX
IIICIIII Cl I1 C
l I IC11Ino
000
*FIXED RESISTORS.*.005%
MAY BE SUBSTITUTED.
3.3,-m-.eeo
I
-USE
SHORT LEADS.
USE SHIELDED LEADS FOR
THE 2 M AND 2 0 M RANGE.
I
I
I
Figure 4-6. Ohms Accuracy Test.
c. Set the resistive decade to zero ohms.
d. Check all ranges listed in I-able 4-7 for the
tolerances indicated.
4-18. AC Normal-Mode Rejection Test.
4-19. The purpose of the test 1s t o verify the ability o f t h e
Mult~metzr to make accurate D C Voltage measurements
In the presence to A C Voltage a t power line frequencies.
Definition: A C Normal-Mode Rejection is the ratio of
the peak normal-mode voltage to the resultant error in
reading.
N M R R (dB)
=
d. Disconnect the short and connect the A C
Calibrator to the Multimeter input. Adjust the
Calibrator output to 7.07 V rms (10 V peak).
e. The Multimeter indication should not vary more
than 0. I0 V o r I0 digits peak from the indication noted in
Step c. This verifies a n A C Normal-Mode Rejection of 40
d H.
f. Repeat Steps c, d, and e for a n A C Calibrator output
frequency of 50 Hz ? 0.1% as monitored by the
Electronic Counter (Period
=
19980 t o 20020 p s ) .
4-21. A C Common Mode Rejection Ratio
-
CMRR.
4-22. Phe purpose of this test is to verify the ability of the
Multimeter to make accurate A C Voltage measurements
a t power line frequencies applied simultaneously to the V
-
Rsand C O M terminals.
Definition: C M R R ( d B )
=
K M S A C Interfering Voltage
Change in ACV reading
1
Peak A C Interfering Voltage
I
4-23. An A C Calibrator a n d Electronic Counter are
Change in DCV reading (i.e.. peak roll)
required for this test.
4-20. An A C Calibrator and Electronic Counter a r e r a . Conncet the A C Calibrator to the electronic
required for this test. counter and adjust for a frequency of 50 H L
+
O.l(;h
(19.980 p s to 20,020 p s).
a. Connect the test equipment as shown in Figure 4-7.
D o not connect the Multimeter a t this time.
b. Set the A C Calibrator for a n output of 10 V rms.
b. Using the Electronic Counter as a monitor, adjust c. Set the Multimeter to the ACV functionand the 2 V
the A C Calibrator frequency t o 60 Hz
+
0.1% (Period -
range. Connect a I K
+
1% resistor between V -
R
a n d
16650 to I6683 p s ) . C O M terminals at the Multimeter front panel.
c. Set the Multirneter function to dcV ( = V ) a n d d. Connect the AC Calibrator between the Multimeter
range to 20 V. Short the Multimeter input a n d note the
V - R terminal (with the I K resistor still in place) a n d
indication. power line ground as shown in Figure 4-8.
AC CALIBRATOR
hp 7 4 5 A
I 1
ELECTRONIC COUNTER
hp 5 3 0 0 A
MULTIMETER
C10111301I C1111I1U01IICIO
Figure 4-7. AC Normal-Mode Rejection Test.
4-5