HP 400D, Инструкция по эксплуатации и обслуживанию

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2) Switch the vtvm to the
1 .
0 volt range and adjust
capacitor C4 for
the
best square wave pattern on the
oscilloscope.
E. BASIC CALffiRATION
GAIN)
Connect a
O.
3 volts rms, 400 cps signal from the
Calibration Generator to the vtvm INPUT. Switch
the vtvm to the 0. 3 volt range and adjust the feedback
control (R29) to
attain
a reading of
O.
30 volts.
F. BASIC CALmRATlON INPITr
1) Connect a 1. 0 volt rms, 400 cps, signal from
the Voltmeter Calibration Generator to the INPUT
of the vtvm under te st. Switch the vtvm to the 1. 0
volt range.
2) The voltmeter indication will normally be 1. 0
volts.
If
the reading is high, decrease the value
of the pad in parallel with R3. H the reading is low,
increase the value of the pad. Resistor R3 and pad
are on the input circuit board.
G.
RECHECK DC
HEATER VOLTAGE
Check
the de
heater voltage by the method given
in paragraph 4-7C .
1f
either electrolytic capacitor in the healer Circuit
has been replaced, a heal-run of several hours
should be allowed. Afler the heat-run to form the
capacitor plates, reset the heater voltage.
H. CHECK CALffiRATION
&
TRACKING
1) Check full
scale
accuracy
of
each voltmeter range.
Use the Voltmeter Calibration Generator. The
calibration should be within :1:2% of full scale for a
400D voltmeter or ±l% of full scale for a 400H or
400L voltmeter. The test voltage should be between
50 cps and
SOO
kc.
Avoid using the power line fre­
quency or a harmonic of the power line frequency.
Refer
to the
accuracy specifications if you
use
a test
frequency outside of this range.
2) Check meter tracking on any mid-range. The
I
volt range is usually convenient. A sticky meter
can cause the vtvm to be outside of the calibration
specifications. Defective diodes for CRI and CR2
can also introduce excessive tracking error. Refer
to paragraph 4-4 for information On replacement
diodes.
1.
CHECK EFFECT OF LINE VOLTAGE CHANGE
1) Connect a sine wave Signal to the INPUT of the
vtvm under test. Use a convenient mid-range and
adjust the input Signal amplitude for a convenient
Sect,
IV
Page 7
reference level such as 0 . 9 . Use any frequency
within the frequency range of the voltmeter. The
line voltage should be at 115 volts for at least two
minutes before setting your reference level.
2} When the line voltage is changed from 115 to
103 or from 115 to 127 volts, the indication on the
vtvm
under test will normally not change from the
reference level by more than :1:2% of full scale after
a two minute period.
These effects are more noticeable at the upper and
lower limits of the vtvm frequency range.
H
the
change is excessive, check tubes V5 through VI in
that order.
J.
RESPONSE
ADJUSTMENT WITH
SPEC. 23679 & 23680 INSTRUMENTS
The following frequency response adjustment pro­
cedure is based upon the use of the dj}Spec. 23679
VTVM Frequency Response Generatorand
the
$Spec.
23680 Wide
Range
Oscillator.
The input voltage to the vtvm. under test
is
essentJally
monitored by the reference meter in the Frequency
Response Generator. The imUcatiOn on this monitor
meter at 400 cps will be called "SET LEVEL"
in the
steps that follow.
Follow
the
procedure
in
paragraph
4-7K
if th
e
Spec.
23679 and Spec. 23680 equipment is not available.
NOTE
The frequency response of
the
instrwnent will prob­
ably not need adjustment. These steps have been
included to verify the instrument response and to
restore proper operation in case the original ad­
justment is altered. Failure to meet any of the
following tests
can
usually be traced to one or more
weak tubes.
1)
Connect a 400 cps sine wave signal to the INPUT
of the vtvm under test. Adjust signal level for a
reading of 0. 90 on the . 001 volt range. Adjust mon­
itor meter
to
"SET LEVEL".
2) Change input signal to
4
me and set amplitude
to " SET LEVEL". Adjust capacitor C21
in
the vtvm
under test for a reading of 0.90.
3) Change input signal to I mc and set amplitude
to "SET LEVEL". Capacitor C26
in
the plate cir­
cuit of V4 can be adjusted in value between limits
of 15 �f and 82 /.ij.tf to control 1 mc response.
H
you change C26, repeat steps
1
through 3.