Specifications

2-13
Averaging function calculates the mean value of measured parameters from the desired number of
measurements. Averaging has the same effect on random noise reduction as that by using a long
measurement time.
Figure 2-11. Relationship of measurement time and precision
2.4.6 Compensation function
Impedance measurement instruments are calibrated at UNKNOWN terminals and measurement
accuracy is specified at the calibrated reference plane. However, an actual measurement cannot be
made directly at the calibration plane because the UNKNOWN terminals do not geometrically fit to
the shapes of components that are to be tested. Various types of test fixtures and test leads are used
to ease connection of the DUT to the measurement terminals. (The DUT is placed across the test
fixture’s terminals, not at the calibration plane.) As a result, a variety of error sources (such as resid-
ual impedance, admittance, electrical length, etc.) are involved in the circuit between the DUT and
the UNKNOWN terminals. The instrument’s compensation function eliminates measurement errors
due to these error sources. Generally, the instruments have the following compensation functions:
• Open/short compensation or open/short/load compensation
• Cable length correction
The open/short compensation function removes the effects of the test fixture’s residuals.
The open/short/load compensation allows complicated errors to be removed where the open/short
compensation is not effective. The cable length correction offsets the error due to the test lead’s
transmission characteristics.