Recalibration; Preparation - IET Labs, Inc. RLC Digibridge 1693 User And Service Manual

1693 RLC Digibridge

5.9 Recalibration

5.9.1 Preparation

Introduction. This service procedure requires a set of
external calibration resistors whose Rand Q values
are exactly known and generally requires a frequency
counter. (Table 5-13) For the frequency correction,
the counter makes a measurement; but for the four
internal resistance standards, the Digibridge makes
the measurements. After recalibration, the Digibridge
retains in RAM the corrections that the microproces-
sor needs to compensate for the small errors in the
actual values of test frequency and internal standard
resistor parameters.
(Therefore, the Digibridge calculates its measurement
results correctly, accomplishing by calculation the
same result that would be obtained if the recalibra-
tion process actually trimmed the internal standards
exactly to their nominal values.]
Required Equipment. Refer to Table 5-13.
Decision "Whether Frequency Calibration is Needed.
The frequency calibration (paragraph 5.9.7) is neces-
sary - and should be completed before recalibrating
any range - if any of the following is true:
• If the "Dallas Chip" has been replaced.
• If oscillator U4 has been replaced.
140
Table 5-13: Equipment required for calibration
Procedure
1. Remove any adaptor that may be in the test
fixture. Inspect the Digibridge test fixture for
cleanliness. If it is dirty or if it is scheduled
for periodic cleaning soon, clean the test
fixture as described in paragraph 5.6.
2. P l a c e a l l e q u i p m e n t i n c l u d i n g t h e
Digibridge(s) to be recalibrated in th e tem-
perature stabilized room, normally at 23°C.
3. Switch Digibridge(s) ON, and if frequency
calibration is needed (see above), switch the
counter power ON. Allow all equipment to
warm up for at least two hours . Leave the
Digibridge test conditions at the defaults.
4. If frequency calibration is needed (see
"Decision ..." above), skip to the procedure
of paragraph 5.9.7 before zeroing and reca-
librating ranges 4, 3, 2, and 1.
Decision whether K Factor Calibration Is Needed.
The K Factor Calibration (paragraph 5.9.8) is neces-
sary and should be completed before recalibrating
any range, if the "Dallas Chip" has been replaced.
Service and Maintenance