multicomp pro MP700499, Руководство пользователя

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Chapter 9 Appendix
9.1 Effect of extended test line and induced voltage
Test lines can usually be extended by customization. If you want to extend the test line, please
contact the dealer or Multicomp-Pro. The user can not extend the test line privately.
Reduce induction voltage
Because the instrument under AC power to test resistance with very small resistance, the inductive
voltage will affect the test. The inductive voltage makes the current in the instrument produce
inductive coupling inside the wire, which will affect the in-line signal. Because the AC current
(reference signal) is 90 degrees different from the phase of the induced voltage, the synchronous
detector circuit can remove the induced voltage when the voltage is low. But when the voltage is
high, the inductive voltage will distort the signal and produce the wrong synchronous detection
signal. The instrument detects the internal inductive voltage, if the voltage rises to a certain height,
will produce the wrong test signal. Reducing the length of the test line, especially the length of the
branch part, will weaken the inductive voltage.
When the standard test line is used, the induced
voltage will affect the deviation of the result value by about 15 dgt.. if the zero adjustment
and the test wiring are extremely different in 3 mΩ range .
9.2 Influence of Eddy Current
The AC current in the instrument will generate eddy current around the metal plate, and the
eddy current will generate inductive voltage inside the test line. Because the phase of the
induced voltage is 180 degrees different from the phase of the AC current (reference current),
the synchronous detection current can not eliminate the induced voltage, which leads to a test
error. Eddy effect is unique to the ohmmeter of AC power supply. The distance between the
metal parts including the metal plate and the test line (branch part) should be reduced to avoid
the influence of eddy current.