Maintenance 6
PERFORMANCE TEST
To initiate the self-tests, press the SRQ button for 3 seconds. The TEST annunciator will then light up, and the 8842A will run through the analog tests in sequence. Each test number is displayed for about 1 second. The instrument can be stopped in any of the test configurations by pressing the SRQ button while the test number is displayed. Pressing any button continues the tests.
After the last analog test is performed, all display segments light up while the instrument performs the in-guard program memory, calibration memory, and display tests. The instrument then assumes the power-up configuration: VDC, autorange, slow reading rate, offset off, local control.
If the 8842A detects an error during one of the tests, it displays the ERROR annunciator and the test number for about 2-1/2 seconds, and then proceeds to the next test. The test number thus becomes an error code. (Error codes are listed in Table 2-1, Section 2.)
Passing all diagnostic self-tests does not necessarily mean the 8842A is 100% functional. The test, for example, cannot check the accuracy of the analog circuitry. If one or more errors are displayed, the 8842A probably requires service.
6-4. DC Voltage Test
The following procedure may be used to verify the accuracy of the VDC function:
1.Ensure the 8842A is on and has warmed up for at least 1 hour.
2.Select the VDC function.
3.Connect the DC Calibrator (see Table 6-1) to provide a voltage input to the HI and LO INPUT terminals. Connections for the Kelvin-Varley Voltage Divider and the Fluke 5440A are shown in Figure 6-1.
4.For each step in Table 6-2, select the indicated range, set the DC Calibrator for the specified input, and verify that the displayed reading is within the limits shown for each reading rate. (For step A, connect a short across the HI and LO INPUT terminals and press OFFSET. The measurement in step C should be relative to this offset.)
5.Set the DC Calibrator to input negative voltage, and repeat steps C thrugh G of Table 6-2.
6.With the unit in the 2V range, check the A/D linearity by setting the DC Calibrator for each step in Table 6-9, while verifying the display reading is within the limit shown. Set the DC Calibrator for zero volts and disconnect if from the 8842A.
