HP 400D Operating And Servicing Manual page 23

The procedure in this manual contains an "alternate
method" for frequency response adjustments.
"alternate method" is based upon using the alternate
Instruments in the following list In place of the Spec.
23679 and Spec. 23660 instruments.
---A
low
distortion oscillator
range from 10 cps to at least 6.4 mc and an out­
at
put voltage of least 3.0 volts nns. The 4jlModeI
650A Test Oscillator will meet these require­
ments.
---An rms reading, average responsing, ac volt­
meter with a known frequency response from
to
cps to 6.4 me. The reference voltmeter can
be an $Model 400H or Model 400L.
of
couple type reference meter can also be used.
Absolute voltage values are not needed when
making frequency respOnse measurements.
4-6 RAPID PERFORMANCE CHECK
The following tests may be used
of the instrument without going through the complete
test procedure. An instrument that passes these
tests will generally meet all specifications, but thts
CANNOT be considered as a complete certification
procedure.
The following equipment is needed for the Rapid Per­
formance Check. See paragraph 4-5 for a detailed
description of these instruments.
A adjustable line voltage source with meter.
n
---
---Voltmeter Calibration Generator.
---Source of a 10 cps sine wave signal with an am­
1.
plitude of at least
All measurements should be made with line voltage
set to li5 volts unless otherwise specified.
A. MODELS 400D or 400H ONLY
II
the instrwnent being checked is a Model 400L,
B
skip to steps and C.
1) Warm-up vtvm for at least 15 minutes and adjust
meter zero as described in paragraph 4-2.
2) Set the vtvm to the 0.3 VOLT range.
0. 3 volt from calibration generator to
Adjust R29 so meter indication is
full scale calibration accuracy on all ranges: :2%
for 400D and :1% for 400H.
B .
MODEL 400L ONL
If
t h e instrument being checked is
400D/H, complete step A and skip to step C.
This
covering
the frequency
A thermo­
to
check the operation
0 volt.
Connect
vtvm
INPUT.
O. 3 volt. Check
Y
a
Model
1) Allow the instrument to heat for at least 15 min­
utes. Set to the . 3 volt range and apply . 3 volt
from the calibration generator, adjust R29 if neces­
sary to obtain a .3 volt indication on the meter.
2) Check the full scale calibration of the remaining
l'auges. !Should all1all
Tllt�y
1
3) Set the 400L to the volt range and feed in I volt.
Check full scale. Drop the input voltage to
The meter should track within 1% of the reading.
Failure to track properly may be due to defective
diodes, a defective V5 or poSSibly the return spring
adjustment in the meter movement has shifted.
return spring adjustment is made by
facturer and cannot be made without removing the
meter movement from its case.
mended that this adjustment
chance that dust Or metal particles may get Into
moving coil system which will completely disable
the movement. The spring setting also affects the
The
full scale setting. meter amplifier gain must be
reset with R29 each time the spring is moved until
a setting is found which gives good tracking over
the whole scale.
C. MODEL 400D, 400H, and 400L
The following measurements should be com­
pleted after either step A or step
to
1) Set line voltage 115 volts.
2) Set the range switch to the
I
a volt 10 cycle sine wave to the INPUT. The abso­
lute input voltage is not important here, you are
merely establishing a reference indication of
3) Reduce the line voltage input to the instrument
to 103 volts and watch the meter indication.
meter indication should not change more than 5%
from the reference established in step 2 after the
instrwnent has been operating
of
for a periOd minutes.
several
Successful completion of these steps indicates that
the instrument will probably meet
If
it will not, it will be necessary to resort to the
complete test procedure in paragraph 4-7.
4-7 COMPLETE ADJUSTMENT AND TEST
PROCEDURE
Usually a particular voltmetet
plete testing and calibration. Only one or two tests
will be needed and they can be done without com­
pleting th test procedure.
e entire
be
basic calibration can
time without making any other adjustments.
W
Sect. Page 5
withIn :1%.
O.
3 volt.
The
the
meter manu­
It
is not recom­
be
made because of the
the
B.
I volt range and apply
I
volt.
The
on
reduced line voltage
all
specifications.
will
not need com­
:F'oi' example,
checked and adjusted at any