Chapter 10 Appendix
10.1 Effects of Extending the Measurement Lead and Induced Voltage
The test lead extension is normally performed by Hioki. If you want extension performed, contact
Regal Electro. Users should not extend the measurement leads.
Reducing Induced Voltage
Since the instrument measures a minute resistance with AC power, it is affected by induced voltage.
Induced voltage refers to voltage that allows the current generated in the instrument to build an
inductive coupling in a lead and affect signal lines. Since the phase of the induced voltage is shifted
from that of the AC current (reference signal) by 90°, it can be eliminated with the synchronous
detection circuit if the voltage is low. But for high levels, the induced voltage distorts the signals,
causing incorrect synchronous detection. The instrument monitors induced voltage internally and
generates an abnormal measurement signal if the level rises above a certain level. Reducing the
length of the lead will lower induced voltage. Reducing the length of the branched section is
particularly effective. Even when using the standard measurement lead, if in the 3mΩ range the lead
placement differs substantially between when the zero-adjust feature was used and when the
measurements were taken, the effects of induced voltage will cause the values to fluctuate by
approx. 15 dgt.
10.2 Effect of Eddy Currents
The AC current generated in the instrument induces eddy currents in the surrounding metallic
plates, which generate induced voltage in the test lead. Since the phase of this induced voltage is
shifted from that of the AC current (reference signal) by 180°, it cannot be eliminated by the
synchronous detection circuit, resulting in measurement errors. The influence of eddy currents is a
phenomenon unique to ohmmeters that measure resistance with AC power. To protect the test lead
from such effects, keep metallic parts, including metallic plates, at a suitable distance from the test
lead (branched section).
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