How to Measure Inductance of a Coil

By Paul Dohrman

Inductors are sometimes wound by the user instead of bought. In such cases, the inductance would not be stamped on the side but instead may need to be found empirically. The best way to measure inductance for an inductor like a coil (solenoid) is to use an inductance bridge or meter. If you have neither, a more indirect way is to use an oscilloscope.

Step 1

Connect a resistor of known resistance and the coil in series with the sine wave oscilloscope.

Step 2

Turn on the oscilloscope and clamp the two clips of one voltmeter to the circuit on opposite sides of the coil to determine the voltage drop across the coil. Then do the same for the resistor with another voltmeter.

Step 3

Set the frequency of the oscilloscope such that the voltage drop across the resistor and inductor are the same. Finding said frequency may be a matter of trial and error. At that frequency, the resistance of the resistor and the impedance of the inductor will be equal.

Step 4

Set the resistor’s resistance and the inductor’s impedance equal to each other and solve for the inductance of the coil. Resistance = 2?fL, where \"f\" is the frequency of the oscilloscope and \"L\" is the coil’s inductance. The resistance of the resistor has not changed from the start; it is independent of the frequency. So \"L\" can be solved for by arithmetic.

About the Author

Paul Dohrman's academic background is in physics and economics. He has professional experience as an educator, mortgage consultant, and casualty actuary. His interests include development economics, technology-based charities, and angel investing.