HP 400E, Operating And Service Manual

Page: 23 / 57

Models 400E/400EL Section Y
SECTION V
MAINTENANCE
5-1. INTRODUCTION.
5-2. This section contains information necessary to
maintain the Model 400E/EL. The following
paragraphs describe the Performance Checks, the
Calibration Procedures. and the Troubleshooting
Procedures.
5-3_ REOUIRED EOUIPMENT.
54. Table 5-1 is a list of the equipment required to
properly maintain the Model 400E/EL. If the model
recommended in Table 5 - 1 is not available, a
substitute may be used as long as it meets the
required specifications.
5-5. MECHANICAL ZERO
(400E Only).
5-6. Before any performance checks or calibration is
begun, complete the mechanical zero adjustment in
the following steps:
a. Be sure the meter has been off for at least
one minute, or momentarily short the meter
terminals.
b. Rotate mecha nical adjustment screw
CLOCKWISE until meter pointer is to the
left of zero and moving upscale toward zero.
c. C o ntinue to rotate adjustment screw
clockwise. STOP when needle is exactly on
zero. If needle overshoots. repeat step b.
d. When pointer is exactly over zero. rotate
a d j u s t m e n t s c r e w s l i g h t l y
COUNTERCLOCKWISE to relieve tension
on suspension. If the pointer moves to the
left, repeat whole procedure, but make
counterclockwise rotation less.
5-7. PERFORMANCE CHECKS.
5-8. The performance checks are "in cabinet" tests
that compare the 400E/EL with its specifications.
These procedures can be used both for incoming
inspection and periodic inspection. The performance
checks should be conducted before any attempt is
made to calibrate the instrument. A Performance
Check Test Card is provided at the end of this section
for recording the performance of the instrument
during the performance checks. The card can be
removed from the manual and used as a permanent
record of the incoming inspection or of a routine
performance check.
5�. ACCURACY AND FREQUENCY RESPONSE
TESTS.
5-10. The accuracy and frequency response tests
compare the Model 400E/EL with its accuracy
specifications. Three methods are given 'in the
following paragraphs. Any one of the three
procedures can be used dependent upon the test
equipment available and the desired accuracy to
which the 400E/EL is to be checked. The procedure
using the -hp- 745A AC Calibrator and the 746A
Amplifier is the simplest and most accurate for all
voltages at frequencies from 10Hz to 1 10kHz. From
1 10kHz to
I
OM Hz, the 652A Test Oscillator can be
used for the 3 and 1 volt ranges with an accuracy of
0.25% (0.75% for lower ranges). The Thermal
Converter Method is more time consuming and
subject to burn-{)ut; but it has an accuracy
uncertainty of 0.04% to 0.1 8%. The E02-738BR can
be used to check all ranges at 400Hz to a minimum of
.3 millivolts. The accuracy at 400Hz is 0.2% at 300
volts and 0.3% using the attenuator. The frequency
response can be checked with a maximum of 3 volts
with the 652A Test Oscillator. The 654A Test
Oscillator can be used below I volt output from 10Hz
to IOMHz with a flatness of 0.5%. This flatness is
without adjusting the amplitude at each change of
frequency.
5-11. Accuracy Check f rom 10Hzto 110kHz.
5-1 2. The test setup in Figure 5- 1 uses the 745A AC
Calibrator System. This calibrator can produce any
voltage level from O.lmY to 100 volts in a seven digit
readout for frequencies from 1 0Hz to 1 10kHz. The
accuracy is from 0.022% to 0.205%. The 746A
Amplifier can be used for voltages above 1 00 volts
with the same accuracy.
For optimum performance, let the
400E/EL and the 745A/746A
warmup for at least one-half hour.
a. Place the 400E/EL on the 3 volt range and
position the 745A to read 3.00000 volts at
400Hz.
b. Connect the test setup as shown in Figure
5- 1. Set the 745A SENSE switch to LOCAL
or if more accuracy is desired place the
SENSE switch to REMOTE and connect the
sense terminals to the input of the 400E/EL.
5- 1