*.
4OOD-2C
Page 3
SECTION
111
-
TEST EQUIPMENT REQUIRED
The following equipment
is
required to test and cali-
brate
@
Vacuum Tube Voltmeter Models 4WD, 400H,
and 400L.
A.
A
dc voltmeter capable of measuring
250,
6.3,
12.6 volts.
This voltmeter must have a
sensitivity
of 1000 ohms/volt or better.
A
vtvm such as the
@
Model 410B
is
satisfactory,
B.
An
@
Model 738AR (formerly
@
Spec. 23678)
Voltmeter Calibration Generator or equivalent.
Model 738AR generator will deliver a 400-cps output
voltage from 0.3 millivolt rms to 300 volts
rms
with
an accuracy of &0.25% and not more than 0.2%
hum
and distortion.
This generator will also supply
+
dc
or -dc voltages from 0.3 millivolt to 300 volts for
calibration of dc voltmeters.
C. An
@
Model 739AR (formerly
@
Spec. 23679)
VTVM Frequency Response Generator. This gen-
erator has an internal signal source to cover
the
fre-
quency range from 350 kc to
11
mc.
Up
to a 3-volt
output signal can be obtained. The internal attenuator
and reference voltmeter are designed for frequencies
from 10 cps to
11
mc. Internal impedance
is
50
ohms.
D.
An
@
Model 200s (formerly
@
Spec. 23680) Wide
Range Oscillator.
This oscillator has an internal
impedance of
50
ohms and will deliver a 3-volt signal
from 5 cps to
600
kc.
Use
with
Model 739AR VTVM
Frequency Response Generator.
b
E.
A
battery operated oscillator covering 60 and 120
cps with an output of at least
1
volt and not more
than
1%
distortion.
F.
A
square wave generator capable of delivering a
2-volt peak-to-peak
1
kc signal, $The @Model
211A
Square Wave Generator or the internal calibrator
in
the
@
Model 150A High Frequency Oscilloscope can
be used.
G.
A
high frequency oscilloscope such as the
@
Model 150A.
H.
The
@
Model 739AR VTVM Frequency Response
Gen-
erator and the
@
Model 200s Wide Range Oscillator
are designed to
be
operated together
when
ma
quency response measurements. These
tw
ments greatly increase the speed and accuracy of
frequency response measurement.
The frequency response adjustment procedure given
in Section
IV
is
particularly suited for use
with
Model 739AR and Model
2005
instruments. The instru-
ments
in
the following list are suitable alternates.
--
A
low distortion oscillator covering the frequency
range from 10 cps to at least 6 or 7 mc and an output
voltage of at least 3.0 volts rms. The
($9
Model 650A
Test Oscillator will meet these requirements,
--
An rms reading, average responding, ac voltmeter
with a known frequency response from 10 cps to at
least 4.0 mc. The reference voltmeter can be an
@
Model 400H or Model 400L.
A
thermocouple type of
reference meter can also be used.
Absolute voltage
values are not needed when making frequency response
measurements.
An
adjustable line voltage source.
SECTION
IV
-
TEST
&
CALIBRATION PROCEDURE
When all the following procedures are to be completed,
they can most easily be done in the order listed. In
many instances, only one or two tests will be needed
and they can be done without completing all other
tests. For example, basic calibration can be checked
and adjusted at any time without making any other
adjustments.
A
10 to 15-minute warmup and a check of
the
power
supply output voltages
is
always recommended before
making any other tests or adjustments.
The specifications for your
@
Model 400D, 400H, or
400L Vacuum Tube Voltmeter are given
in
the front
of the manual supplied
with
the
vtvm.
The following
test procedure contains extra checks to help you
analyze a particular instrument.
These extra checks
and the data they contain cannot be considered as
specifications.
NOTE: The test frequencies and the voltages specified
in
many of the steps
in
this
procedure are based upon
the use of
the
test equipment listed
in
Section 111. Other
frequencies and voltages can be used,
Any
vtvm can be
adjusted for optimum performance on the range you
most commonly
use.
L
00665-2
A.
SETTING MECHANICAL
ZERO
IN
MODELS 400D
QQ
1)
Allow
400D
20
minute warm up. Turn instrument
off.
2)
Rotate mechanical zero-adjustment screw clock-
wise
until
meter pointer
is
to
left
of zero and moving
upscale toward zero.
Continue to rotate adjustment
screw
clockwise;
stop
when pointer
is
right on zero,
If
pointer
overshoots zero, repeat
this
adjustment.
3)
When pointer
is
exactly on zero, rotateadjustment
screw approximately 15 degrees counterclockwise.
This
is
enough to free adjustment screw from the
meter suspension,
If
pointer moves during this
step repeat entire adjustment.
B.
SETTING MECHANICAL ZERO
IN
MODEL 400L
The special meter
in
the 400L
is
adjusted
with
the vtvm turned on since the meter pointer rests
against the stop at the left end of the scale
when
the
instrument
is
turned off.
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