Prbimbal; Bias Comp; Bias Error - Tektronix 11A52 Service Manual

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Test Failure
The test failure may be caused by a faulty probe, bad probe-to-amplifier connection, amplifier signal path
problems, or by a faulty probe fine offset ACVS channel.
PRBIMBAL
This routine checks the error the calconstants used to balance the amplifier when a Level 2 active probe is
installed. The test produces meaningful results only when a Level 2 probe is connected, and has been run through
a probe calibration cycle. The test generates a percentage error, which must fall within a ±2% range. If the
error bounds are exceeded, the test is flagged as failed.
Test Failure
Failures here may be caused by a faulty probe, bad probe-to-amplifier connection, or amplifier signal path
problems.
BIAS COMP
This routine checks the calconstant used to compensate for input bias current in the input stages of the amplifier.
The Bias Camp calconstant is generated during the amplifier calibration cycle, and loaded into the ACVS
system to generate a voltage that cancels the input bias to prevent a voltage from being present at the
amplifier's input connector. The test ensures that the resulting calconstant is within the allowable range of
ACVS Bias correction adjustment. The allowable range is from -0.999 to +0.999. If the calconstant indicates
, that more adjustment is needed than the circuitry provides, the test is flagged as failed.
Test Failure
The test failure may be caused by a failure in the ACVS channel used for bias compensation, or by M377's with
excessive input current.
BIAS ERROR
This routine is a check and balance on the bias compensation algorithm. In amplifier calibration, the bias
compensation algorithm is iterative. The bias error test checks to ensure that the results of the iterative
calculations are properly converging on a reasonable bias compensation value.
The results returned by the Bias Error test depend heavily on the algorithms used to generate the bias
compensation correction, and have little or no meaning unless the user has a thorough understanding of the
numerical methods used during the bias compensation part of calibration in the 11A52. .
Test Failure
By virtue of the algorithm design, it should be impossible for this test to fail by itself. However, if the Bias
Comp test fails, this test may fail as a byproduct.
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11A52 Extended Service Manual