Giga-tronics 8650A Series, Operation Manual

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Series 8650A Universal Power Meters
2-42 Manual 31470, Rev. E, April 2001
2.3.22 Sources of Error
In the previous accuracy verification procedure, there are four sources of error:
• Source output level variation
• Power splitter output tracking
• Power meter X total measurement uncertainty
• Power meter Y total measurement uncertainty
Worst case uncertainty, which should be used for calibration purposes, is the arithmetic sum of all four
of these sources of error.
Source output level variation occurs in all microwave sources. This happens when the signal source
output level changes during the time it takes to record the displayed value on power meter X and then
to read the displayed value on power meter Y. This source of error can be minimized by using a
laboratory grade signal source.
Power splitter output tracking errors are the maximum signal level variation at the splitter X output as
compared to the splitter Y output.
Total measurement uncertainty for each of the power meters is the worst case combination of mismatch
uncertainty, instrument accuracy, and sensor accuracy.
Mismatch uncertainty is calculated from the reflection coefficients of the sensor and the splitter
(source) according to the following formula:
For a source mismatch specified in terms of return loss (RL), the equation should be modified according
to:
The following factors affect instrument accuracy:
• Instrument linearity or instrumentation uncertainty
• Reference calibrator setability or power reference uncertainty
The following factors affect sensor accuracy:
• Calibration factor uncertainty
• Calibrator to sensor (or power reference to sensor) mismatch uncertainty
• Noise
• Zero set
• Calibration pad uncertainty (for thermal-based power meters only)
• Sensor linearity