HP 400D, Operating And Servicing Manual

Page: 23 / 50

The procedure in this manual contains an "alternate
method" for frequency response adjustments. This
"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
covering
the frequency
range from 10 cps to at least
6.4
mc and an out­
put voltage of
at
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. A thermo­
couple type
of
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
to
check the operation
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
n
adjustable line voltage source with meter.
---Voltmeter Calibration Generator.
---Source of a 10 cps sine wave signal with an am­
plitude of at least 1. 0 volt.
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,
skip to steps B 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. Connect
0. 3 volt
from calibration generator to
vtvm
INPUT.
Adjust R29 so meter indication is
O.
3 volt. Check
full scale calibration accuracy on all ranges: :2%
for 400D and :1% for 400H.
B. MODEL 400L ONL
Y
If the instrument being checked is
a
Model
400D/H, complete step A and skip to step C.
Sect.
W
Page 5
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.
Tllt�y
!Should all1all
withIn :1%.
3) Set the 400L to the
1
volt range and feed in I volt.
Check full scale. Drop the input voltage to
O.
3 volt.
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. The
return spring adjustment is made by
the
meter manu­
facturer and cannot be made without removing the
meter movement from its case.
It
is not recom­
mended that this adjustment
be
made because of the
chance that dust Or metal particles may get Into
the
moving coil system which will completely disable
the movement. The spring setting also affects the
full scale setting.
The
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 and 400L
The following measurements should be com­
pleted after either step A or step B.
1)
Set line voltage
to
115 volts.
2) Set the range switch to the I volt range and apply
a I 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
I
volt.
3) Reduce the line voltage input to the instrument
to 103 volts and watch the meter indication. The
meter indication should not change more than 5%
from the reference established in step 2 after the
instrwnent has been operating
on
reduced line voltage
for a periOd
of
several
minutes.
Successful completion of these steps indicates that
the instrument will probably meet
all
specifications.
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
will
not need com­
plete testing and calibration. Only one or two tests
will be needed and they can be done without com­
pleting th
e entire
test procedure. :F'oi' example,
basic calibration can be checked and adjusted at any
time without making any other adjustments.