Fluke 5790B, Руководство по обслуживанию

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5790B
Service Manual
3-6
12. If the readings in step 14 and 15 differ by more than 0.5 µV the BALANCE
control is not properly adjusted and the Self Calibration process has to be
repeated from step 1.
13. Set the CALIBRATE switch to 100:1+. Adjust the 100:1 CALIBRATE
adjustment until the reading is 0
±
0.5 μV.
14. Push

on the 5730A.
15. Set the CALIBRATE switch to OPERATE and the MODE switch to the
necessary position.
16. This completes the self-calibration of the 752A.
Note
1. The 10:1 adjustment must be done before the 100:1 adjustment.
2. Follow the “Self-Calibrate a Fluke 752A Divider with a Fluke
8508A as the Null Detector” procedure. Adjust the 752A to within
0.09 µV/V or less of the nominal ratio for 10:1 and 0.18 µV/V or
less for 100:1.
3. Be sure the 752A is well stabilized in a constant temperature
environment before calibration starts. The instrument stays
calibrated as long as the temperature remains constant.
4. It can be difficult to adjust the BALANCE control for a difference
of exactly 0 μ V but it is not necessary to get it to exactly zero to
get good results. Instead, adjust the BALANCE for as close to
zero as is practical but a difference as large as 1 μ V is still
acceptable. Then adjust the 10:1 or 100:1 CALIBRATION
adjustment for a reading that is the same for the switch in the
10:1+ position as the 10:1- position but opposite sign. For
example, if the BALANCE difference is 1 μ V, then adjust the
appropriate CALIBRATION adjustment until one switch position
is say +0.5 μ v and the other position is -0.5 μ V. These two
readings do not have to be the same to meet the
±
0.5 μ V
requirement given in the procedure. To determine if the
adjustment is close enough:
Take the reading in the 10:1+ position and add it to the reading
in the 10:1- position and then divide the result by two. For
example, if the reading in the 10:1+ position is +0.75 μ V and in
the 10:1- position is -0.25 μ V then: (+0.75 μ V+(-0.25 μ V))/2 =
+0.25 μ V. This meets the requirement for an adjustment to within
±
0.5 μ V.
5. Using a DMM takes longer and more care is necessary to self-
calibrate a 752A than using a Fluke 845, but it can still be done
in a reasonable time once you get used to the new technique.
You need to determine which settings of the 8508A work best.
Settings such as the number of digits (7 or 8), using FAST, or
using the FILTER, can be tried until a combination is found that
works best. It may be that one set of settings is found to be best
for the initial adjustments and then a change in the settings for
the final adjustment is necessary. For example, it may work best
to set up the meter to respond quickly to a change in voltage to
get the adjustments close then change to a setting that takes
longer per reading but has less scatter for the final readings.