Agilent Technologies 85054D, User'S And Service Manual

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85054D 1-9
General Information
When to Calibrate
When to Calibrate
A network analyzer calibration remains valid as long as the changes in the systematic
error are insignificant. This means that changes to the uncorrected leakages (directivity
and isolation), mismatches (source match and load match), and frequency response of the
system are small (<10%) relative to accuracy specifications.
Change in the environment (especially temperature) between calibration and
measurement is the major cause in calibration accuracy degradation. The major effect is a
change in the physical length of external and internal cables. Other important causes are
dirty and damaged test port connectors and calibration standards. If the connectors
become dirty or damaged, measurement repeatability and accuracy is affected.
Fortunately, it is relatively easy to evaluate the general validity of the calibration. To test
repeatability, remeasure one of the calibration standards. If you can not obtain repeatable
measurements from your calibration standards, maintenance needs to be performed on the
test port connectors, cables and calibration standards. Also, maintain at least one sample
of the device under test or some known device as your reference device. A verification kit
may be used for this purpose. After calibration, measure the reference device and note its
responses. Periodically remeasure the device and note any changes in its corrected
response which can be attributed to the test system. With experience you will be able to see
changes in the reference responses that indicate a need to perform the measurement
calibration again.