Using Dip Meter to Measure Inductance

The dip meter of grid dip oscillator can be used to measure many parameters including the inductance of an inductor.

Dip Meter Tutorial Includes:
Dip meter / GDO basics How to use a dip meter / GDO Using GDO to measure inductance Using GDO to measure capacitance Measuring antenna resonant frequency Measuring feeder electrical length

The grid dip meter or grid dip oscillator, GDO is a very versatile test instrument. It can be used to measure many parameters. Some measurements are made directly and quite obvious - others are less obvious, but nevertheless the dip meter is able to make some useful measurements of a variety of parameters.

One such measurement that the dip meter can make is that of the inductance of an unknown inductor.

How to measure inductance with a dip meter

The method used to measure the inductance of an unknown inductor with a grid dip meter is relatively straightforward. The method used involves using a known capacitor in parallel with the unknown inductor to make parallel resonant circuit.

With the known capacitor connected, the grid dip meter or grid dip oscillator can be used in the normal way to determine the resonant frequency of the resonant circuit.

Once the resonant frequency has been found it is a relatively straightforward calculation to determine the value of the inductor. It can be found from the formula:

L = \frac{1}{4 Π^{2} f^{2} C}

Where
π = 3.142
f = frequency of resonance (i.e. point of the maximum dip)
C = value of capacitor in Farads
L = value of the inductor in Henries

Precautions

There are a number of precautions that should be observed to give the best results:

Using different capacitors yields different results: If an inductor is measured using this method with a dip meter using different capacitor values, then slightly different inductance values will be deduced. The reason for this is the distributed capacitance of the inductor. If the inductor has a metal core, this will also cause inductance to vary with frequency. As a result, it is best to check any inductors near the frequency of intended use.

Although this is not the most accurate method of determining the value of an inductor, it works very well if no other methods are available. It certainly gives results that are as accurate as are needed for most applications.