This is a method to measure inductance (L) of a sample inductor. This is done by putting in series a Resistor of known value, and an Inductor of unknown value.
A sine wave A.C. supply of known stable frequency is introduced to the circuit. A voltage across these components is then measured. We can use a step-down transformer to provide a lower A.C. supply voltage.
VL - Voltage difference of Inductor
VR - Voltage difference of Resistor
Use a Multimeter or Voltmeter to measure
the voltage difference on Resistor (VR) and Inductor (VL).
Calculate value of inductance of the inductor specimen being tested using formula below.
Assuming Inductor has negligible resistance
L (mH)= 3.1831 x R x (VL/VR) for f = 50Hz
L (mH)= 2.6526 x R x (VL/VR) for f = 60Hz
If Inductor has measureable resistance
L (mH)=3.1831xRx (VL/VR - Rz/R) for f = 50Hz
L (mH)=2.6526xRx (VL/VR - Rz/R) for f = 60Hz
where Rz is the Resistance of coil Inductor
The above formula si derived from these formula which can be used for any frequency range.
L = (R/2πf) x VL/VR units in Henry's
f - Sine Wave frequency in Hz
R - Resistor value in Ohms
The accuracy of measurement relies only on the precision of your Multimeter or Voltmeter.
A voltmeter that can measure as small as millivolt at two decimals would bring you 95% accuracy or more.
You can use this simulated circuit in parallel to your actual circuit to verify your result.
Invest to use a resistor that is 1% or less tolerance for more stable and accurate result.
You may need several value of resistor to cover more range of inductance value.
For example, for an inductor in 500uH or less, you may need a small value resistor from 1-Ohm to as small as 10 milliohms.
And for larger inductor from 1mH to as large as 10H, a 1-Ohm to as much as 1K resistor.
