Self-Inductance Meter

EE September 1988 SELF-INDUCTANCE METER Measuring self-inductance reliably is notoriously difficult and inductance meters are, therefore, few and far between and also quite expensive. The instrument described here offers reasonably accurate (within 1%) measuring of low-frequency inductors from 10pH to 2 H. One of the reasons that the measurement of inductance is so tricky is that the value of inductance varies considerably with the conditions of measurement. The principal reason for the variation in inductance is the variation of per- meability, which changes with the level of the test signal and the d.c. bias. Principle of meter When a non-constant current is passed through an inductance, an e.m.f., u, is induced whose magnitude depends on the rate of change of current, di, in a unit of time, dt , i.e. u =L(di/dt). If di/dt is kept constant ( = k) by increas- ing or decreasing the current uniformly, u =Lk that is, the e.m.f. is directly proportional to the inductance (see Fig. 1)...