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2.8.3.5.1 Reference Test
The ADC measures and compares its internal reference with the PMC's precision DC voltage
reference source. The measurement is performed using the current measurement circuitry. If an
out-of-bound condition exists, the measurement is repeated using the voltage measurement
circuitry. If the out-of-bound condition persists, a FAIL message is displayed.
2.8.3.5.2 Sample and Hold Test
This test is performed in two steps. The precision reference is measured as described in the
reference test above and the result is stored. Next, the sample and hold circuitry is placed in the
hold mode, and the reference input is removed. After a period of time the reference measurement
is repeated. The hold measurement and the original reference measurement values should agree
within a prescribed limit in order to pass the test. A FAIL message is displayed if an unacceptable
drift is detected in the hold value.
2.8.3.5.3 ADC Test
Operation of the PMC analog to digital converter (ADC) is verified by comparing the ADC's
response to various known input signals. Detection of an out-of-limit measurement value results
in the display indicating FAIL. If shown, corrective maintenance of the ADC circuitry is needed.
2.8.3.6 CURRENT MEASUREMENT TEST
The current measurement circuitry is validated first. Each of the 5 PMC current output ranges are
then exercised at the maximum current value for each range (the 10 A range is tested at 2 A). In
the event of a measurement failure, the PMC DEBUG UTILITIES, (see Sec. 2.8.4.1) can be used
to display measurement values and provide additional operational data for localizing a fault or for
aid in setting manual adjustments.
The following tests are performed to assess the PMC current measurement and output functions.
2.8.3.6.1 Current Measurement Offset Test
The output of the current measurement amplifier is tested with a zero-voltage, input signal. The
amplifier output must be less than a prescribed value or a FAIL message is displayed.
2.8.3.6.2 DC Current Measurement Gain Test
The PMC's precision reference is measured using the PMC's DC current measurement circuitry.
The measurement amplifier's DC gain value is then compared with the expected value and a FAIL
message is displayed if the difference falls outside a prescribed limit.
2.8.3.6.3 AC Current Measurement Gain Test
The PMC precision reference is measured using the AC current measurement circuitry. The AC
measurement amplifier's gain value is then compared with the expected value and a FAIL message
is displayed if the difference falls outside a prescribed limit.
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