HP 4001, Организационное, ДС, ГС и ремонтное руководство на уровне базы, Страница: 35 / 73

TM 11-6625-1514-15
Section V
Paragraph 5-27
e. Setting the 20-kc and 4-mc frequency response
of the input divider.
NOTE
It is important to follow the complete procedure
in the order given, instead of attempting individ-
ual adjustments which might appear to correct
a certain fault in calibration.
5-27. Although a special voltmeter calibrator instrument
and frequency response test set (listed in paragraph 5-5)
are shown for calibrating the voltmeter, other precision
a-c voltage sources having the required accuracy may
be used for this calibration procedure. In the following
procedure, the mechanical meter zero-set and the
regulated B+ voltage must already be correctly set
(see paragraphs 5-7 and 5-20, respectively). Proceed
as follows:
a. Connect voltmeter calibrator and voltmeter under
test as shown in figure 5-6. (Do not turn on.)
b. Provide a ground-level input to the voltmeter to
check for stray pickup between the instruments by setting
the voltmeter calibrator controls as follows:
OUTPUT SELECTOR to 400~ RMS
RANGE SELECTOR switch to 1.5-5
VOLTAGE SELECTOR switch to 0
POWER switch to ON
c. Set the RANGE switch on the voltmeter under test
to .001 volt, and the Power switch to ON. Allow at
least a ten-minute warmup. Refer to paragraph 3-12
of this manual and to the manual for the Model 738BR
Voltmeter Calibrator for a procedure to test for ground
currents. Eliminate any ground currents by breaking
ground loops as directed in paragraph 3-12.
d. To test the .001 volt range, set the voltmeter cali-
brator to .001 volt and the voltmeter RANGE switch to
.001. If necessary, adjust R107 (figure 5-3) to obtain
a reading of exactly 1 on the 0 to 1 VOLTS scale on the
panel meter of the voltmeter under test. This sets the
gain of the amplifier at audio frequencies.
e. Set the RANGE switch on the voltmeter to the 1-
volt range. Set the voltmeter calibrator to 1 volt, to
test this range. If necessary, adjust R101 (figure 5-3)
to obtain a reading of exactly 1 volt on the voltmeter.
This sets the division ratio of the input voltage divi-
der at audio frequencies.
f. Connect the frequency response test set, the
oscillator, and the voltmeter under test as shown in
figure 5-7. Observe grounding precautions described
in step c.
g. On the frequency response test set, set the OUTPUT
ATTENUATOR to .001, the RANGE SELECTOR to
EXTERNAL, and turn the Power switch ON. This
adjusts the frequency response test set to provide an
output from the external oscillator for the voltmeter
.001 -volt range.
h. Set the RANGE switch on the voltmeter under test
to .001.
i. Set the oscillator for 400 cps output frequency and
adjust its output level to obtain a reading at 0.9 on the
voltmeter scale.
j. Adjust the frequency response test set METER SET
control to obtain a meter reading at SET LEVEL on the
test set. This standardizes the monitoring point of the
output level.
k. Set the RANGE SELECTOR and FREQ. TUNING
controls of the frequency response test set for 4-mc
output frequency and adjust the AMPLITUDE control
to provide a reading at SET LEVEL on the meter.
l. If necessary adjust C102 (figure 5-3) to obtain a
reading at 0.9 on the voltmeter under test. This sets
amplifier gain at video frequencies.
m. While watching voltmeter under test, adjust the
frequency response test set FREQ. TUNING control
from 4 to 10 Mc while holding output level constant
with AMPLITUDE control. The frequency response
curve increases from 4 to approximately 6 Mc and
then drops off from approximately 6 to 10 Mc. The
frequency response of instrument is within specifi-
cation if voltmeter reading remains in 0 to 0.92 range.
If not in specifications adjust R119 and repeat steps
g through l.
NOTE
Whenever R119 is adjusted, both lo- and hi-
freq. response is affected and must be retested.
n. Readjust oscillator and frequency response test
set for 20 cps output and a SET LEVEL indication on
the test set meter. If necessary adjust R118 (figure 5-4)
to obtain a reading at exactly 0.9 on the voltmeter under
test.
o. Repeat step n at a frequency of 10 cps, for a volt-
meter reading between 0.85 and 0.95 (±5%). If 10 cps
response is outside this range, readjust R118 slightly
to bring 10 cps response within the specified limits.
p. Repeat the 400-cps to 4-mc frequency response
check (steps g through k) on the .003 volt range of the
voltmeter and if necessary adjust C14 (figure 5-4) to
obtain a reading of 0.9 on the voltmeter at 4 mc.
q. Repeat the 400-cps to 4-mc frequency response
check (steps g through k) on the 0.01 volt range of the
voltmeter and if necessary adjust C16 (figure 5-4) to
obtain a reading of 0.9 on the voltmeter at 4 mc.
r. On the 1-volt range of the voltmeter, measure
frequency response at both 20 kc and 4 mc using a
procedure similar to steps g through k . At 20 kc if
necessary adjust C4 (figure 5-3) to obtain a reading
of 0.9 on the voltmeter. At 4 mc if necessary pad the
value of R6 (figure 5-3) to obtain a reading between
0.85 and 0.95 (±5%). R6 consists of several resistors
connected in parallel. Increasing the value of one of
these resistors raises the meter reading at 4 mc. The
input shield must be in place on the voltmeter chassis
when making this reading.
00102-4
5-9