Agilent Technologies 4294A Specifications download pdf (Page 26)

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 2-10. 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 uti-

lized 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

residual 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 func-

tions:

• Open/short compensation or open/short/load compensation

• Cable length compensation

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 com-

pensation is not effective. The cable length compensation offsets the error due to the test lead’s

transmission characteristics.

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Agilent Technologies 4294A Specifications Page 26