Specifications

4.8.3 A difference in open/short compensation conditions
Improper open/short measurements deteriorate the accuracy of compensated measurement results.
If the open/short measurement conditions are not always the same, inconsistent measurement val-
ues will result. Each short device has its inherent impedance (inductance) value and, if not defined
as zero or an appropriate value, the difference of the short device used will produce resultant mea-
surement discrepancies. Effective impedance of the short device will vary depending on how it con-
tacts to the measurement terminals. When the bottom-electrode test fixture is used, contact points
on the measurement terminals will be different from the case of the parallel-electrode test fixture, as
shown in Figure 4-20. If the short device is not straight (slightly curved), the measured impedance
will be different depending on which side of the device comes upside. These effects are usually
small, but should be taken into considerations especially when performing a very low inductance
measurement, typically below 10 nH.
Figure 4-20. Difference in short impedance by test fixture types
4.8.4 Electromagnetic coupling with a conductor near the DUT
Electromagnetic coupling between the DUT and a metallic object near the DUT varies with mutual
distance and causes variance in measured values. Leakage flux generated around inductive DUT
induces an eddy current in a closely located metallic object. The eddy current suppresses the flux,
decreasing the measured inductance and Q factor values. The distance of the metallic object from
the DUT is a factor of the eddy current strength as shown in Figure 4-21 (a). As test fixtures contain
metallic objects, this is an important cause of measurement discrepancies. Open-flux-path inductors
usually have directivity in generated leakage flux. As a result, measured values will vary depending
on the direction of the DUT. The difference in the eddy current due to the leakage flux directivity is
illustrated in Figures 4-21 (b), (c), and (d).
If a parasitic capacitance exists between the DUT and an external conductor, it is difficult to remove
the effect on measurement because the guarding technique is invalid. Thus, the DUT should be sepa-
rated from the conductor with enough distance to minimize measurement errors.
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