What is the calibration interval for the 8901B power meter and AM/FM calibrators?
If the unit is left powered up and the temperature is stable, calibrating once a week is no problem, and calibrating once a month may be possible if nothing happens to the power sensor like over power or mechanical shock.
As suggested, a means of doing a quick check to verify that the calibration has not drifted unacceptablely should be implemented. The idea of switching the 8657A through the interface would work fine.
The AM/FM calibrators were designed to verify that the 8901A/B is meeting its +/-1% AM/FM accuracy specification. So when the AM/FM calibration routines are run using the calibrators, as long as the reading is between 99% and 100%, the 8901B is calibrated. This should remain within these limits for better than one year. Agilent employees with a lot of experience with this have seen units 5 years old still meeting the +/-1% specification.
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