Measurement Errors And Their Characteristics; Drift Errors; Random Errors - Agilent Technologies ENA Series User Manual

Calibration

Measurement Errors and their Characteristics

Measurement Errors and their Characteristics
It is important to understand the factors contributing to measurement errors in order to
determine the appropriate measures that should be taken to improve accuracy.
Measurement errors are classified into three categories:
•

Drift errors

•

Random errors

• Systematic errors
Drift Errors
Drift errors are caused by deviations in the performance of the measuring instrument
(measurement system) that occur after calibration. Major causes are the thermal expansion
of connecting cables and thermal drift of the frequency converter within the measuring
instrument. These errors may be reduced by carrying out frequent calibrations as the
ambient temperature changes or by maintaining a stable ambient temperature during the
course of a measurement.
Random Errors
Random errors occur irregularly in the course of using the instrument. Since random errors
are unpredictable, they cannot be eliminated by calibration. These errors are further
classified into the following sub-categories depending on their causes.
• Instrument noise errors
• Switch repeatability errors
• Connector repeatability errors
Instrument noise errors
Instrument noise errors are caused by electric fluctuations within components used in the
measuring instrument. These errors may be reduced by increasing the power of the signal
supplied to the DUT, narrowing the IF bandwidth, or enabling sweep averaging.
Switch repeatability errors
Switch repeatability errors occur due to the fact that the electrical characteristics of the
mechanical RF switch used in the measuring instrument change every time it is switched
on. These errors may be reduced by carrying out measurements under conditions in which
no switching operation takes place.
(You don't need to worry about these errors since the E5070B/E5071B does not have
mechanical RF switches).
Connector repeatability errors
Connector repeatability errors are caused by fluctuations in the electrical characteristics of
connectors due to wear. These errors may be reduced by handling connectors with care.
94 Chapter 4