Range Check; Meter Tracking; Output Calibration; Frequency Response - HP 428B Operating And Service Manual

Model 428B
5-12. Allow a 30 minute warmup and stabilization
period before conducting the following performance
checks.

5-13. RANGE CHECK.

5-14. Figure 5-3 illustrates the test arrangement
recommended. A de meter calibrator is required for
this test.
a. Zero the 428B on the 1 mA range.
b. Switch the 428B and the meter calibrator to the 10
amp range. Set the meter calibrator for 5 amps of
output (maximum output for the recommended
6920B). Connect a test lead between the output
terminals of the meter calibrator and loop the test
lead through the jaws of the 428B twice (see
Figure 3-3). The 428B should read 10 amps ± 0.3
amp.
c. Switch the meter calibrator to the 1 amp range and
adjust it for 1 amp of output. Remove the test lead
from the 428B Probe jaws. Zero the 428B, then
loop the test lead 3 times through the 428B probe
jaws. Switch the 428B to the 3 amp range. The
428B should read 3 amps ± 90 mA.
d. Remove the test lead from the 428B probe jaws
and zero set the 428B. Clamp the jaws over the
unlooped lead after switching the 428B to the 1
amp range. The 428B should read 1 amp ± 30 mA.
e. Continue to downrange the 428B and the meter
calibrator as in Steps c and d and as guided by the
Performance Check Test Card. Where possible,
keep the calibrator at full output to take advantage
of the greater accuracy; this consideration applies
to any meter calibrator which is specified at full
range (or full-scale) output. Note that there will be
a small residual magnetism induced in the probe
by the 10 amps of current that have been passed
through the probe, and that it is good practice to
degauss the probe before using the 1 mA range.

Figure 5-3. Range Check.

15

5-15. METER TRACKING.

5-16. The test arrangement and equipment required
for this test are the same as for Paragraph 5-13.
a. Zero the 428B on the 1 mA range.
b. Switch the 428B to the 100 mA range. Switch the
meter calibrator to the 10 mA range and adjust for
10 mA of output. Connect a long, thin test lead to
the output terminals of the meter" calibrator and
loop the lead ten times through the jaws of the
428B probe. Read 100 mA ± 3 mA on the 428B.
Remove the test lead from the jaws of the probe
one loop at a time and check the linearity of the
readings. Each reading should be within 3 mA of
nominal (e.g. 90 ± 3 mA, 80 ± 3 mA. etc.).

5-17. OUTPUT CALIBRATION.

5-18. A meter calibrator and a one kilohm resistor are
required for this test.
a. Switch the 428B and the meter calibrator to
the 100 mA range. Connect a test lead
between the meter calibrator output leads and
clip the 428B probe to the lead.
b. Set the meter calibrator to 100 mA output and
read full-scale on the 428B.
c. Connect a voltmeter to the output jack of the
428B. In parallel with the 1000 ohm resistor.
d. The voltmeter should read 0.73 V ± 10 mV.

5-19. FREQUENCY RESPONSE.

5-20. A 50 ohm resistor and a function generator are
required to complete this check.
a. Connect a 50 ohm resistor to the high output
jack of the function generator.
b. Turn the 428B RANGE switch to 100 mA then
clip the 428B probe around the resistor lead.
c. Set the function generator to:
Range: .0001
DC Offset: 0
d. Upon the first up-scale alternation to the 428B,
set the function generator Output Level control
for a full-scale reading on the 428B.
e. Connect the vertical input of the oscilloscope
to the output jack of the 428B.
f. Set the coupling of the oscilloscope input to
DC. Set sensitivity and vernier to display
variations of the 428B output as a 10
centimeter peak -to-peak signal.
g. Set the function generator to the sine function.
h. Slowly raise the frequency of the function
generator output using the frequency dial and
function switch as necessary to bring the
output to 400 Hz. Watch the oscilloscope,
looking for the lowest amplitude of peak
deflection.
i. The peak-to-peak level of the waveform
should not drop below 7 centimeters (-3 dB).
Function: Square
Frequency Dial: 5