Specifications

5-13
Furthermore, the following phenomena may occur when a cored inductor is measured using an
auto-balancing bridge type instrument.
When a high level test signal is applied to an inductor, measurement may be impossible for a certain
frequency range. This is because the nonlinearity of the core material causes harmonic distortion of
the test signal current, which hinders measurements. If excessive distortion current flows into the
Lpot terminal of the instrument, it causes the bridge unbalance status (see Figure 5-17 (a).) To
reduce the effects of core material nonlinearity, decrease the test signal level. If the measurement
frequency is fixed, it is possible to reduce the distortion current flow into the Lpot terminal by
connecting a low-pass filter (LPF) at the Lpot terminal as shown in Figure 5-17 (b).
When a high level DC bias current is applied to an inductor, measurement may be impossible for a certain
frequency range. This is because test signal distortion is caused by the magnetic saturation of the
inductor core under the applied bias magnetic field. To reduce the effects of core material nonlin-
earity, take the same precautions as those for measurement at a high test signal level.
When a test cable is used to measure low-value inductors, measurement may be impossible for certain
values of inductance at higher frequencies. This is caused by resonance resulting from the DUT’s
inductance and the capacitance of Hp and Hc cables. In this case, the capacitance of the cables
should be changed so that the resonant frequency shifts to a much higher frequency than the maxi-
mum test frequency required. Reduce the length of the Hc and Hp cables or use another type of
cable to decrease the capacitance.
Figure 5-17. Harmonic distortion caused by inductors