Fluke NetDAQ 2640A, Service Manual

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Theory of Operation
Inguard Software Description
2
2-63
Self-Test Command 2-121.
The self-test command from the outguard causes the following tests to be performed, in
the order given. If the A/D test fails, the tests that require the A/D (zero offset test,
reference balance test, ohms overload test) are not done.
A/D Test 2-122.
This test simply triggers the A/D and waits for either the A/D interrupt or a timeout. If
the timeout occurs before receiving an A/D interrupt, the test fails and the A/D is
assumed to be non-functional. The timeout is set to 10 ms, greater than either the 2640A
or 2645A A/D reading time.
Zero Offset Test 2-123.
The zero offset test measures the four zero offsets, and ascertains that they are within
reasonable limits. The test fails if any of the offsets measures greater than 2000 counts
(2645A) or 12000 counts (2640A). This is approximately 0.175 volts. A typical zero
offset measurement is approximately 0.1 volts.
Reference Balance Test 2-124.
The reference balance test measures the two reference balance values. The individual
counter values (N counts and P counts) are tested against limits, as are the differences
between the counter values. For both references on, each counter must be less than
0x8000, and their difference must be less than 0x6000. For both references off, each
counter must be less than 0x2000, and their difference must be less than 0x200.
Ohms Overload Test 2-125.
For this test, a two-wire ohms measurement is attempted without any channel selected
(however the tree and function relays must be set). This should result in an overload.
Any other value causes the test to fail.
OTC Test 2-126.
The OTC test attempts to do an open-thermocouple check with no channel selected.
Unless this results in an “open” indication, the test fails.