Introduction
I only occassionally need to measure the value of an inductor, however my current two multimeters don’t support inductance measurement. In addition the meters that do are quite expensive and often don’t have very good ranges especially down in the lower inductance range.
I do however own a fairly accurate frequency meter so I thought of building this project which is essentially a basic LC oscilator with the frequency given by the standard LC tank frequency relationship.
fc = 1/(2*Pi*sqrt(L*C))
The PCB is assembled on a single sided board and uses a basic comparator with hysteresis, a BNC socket is provided to connect directly to a frequency counter.
The button on top of the allows the board to operate with two different parallel capacitors giving two different ranges as a validation of the reading if required. This might be important where an inductor has a large amount of parastic capacitance, in my case I simply average out the two readings.
As can be seen from the photos below, though hole trimmers allow the adaptor to be calibrated for a capacitance with a nice round value to simplifiy the calculation mentioned above.
Images
The Low cost inductance meter adaptor is assembled in a off the shelf box which I brought from Jaycar electronics, measuring 80x50x30mm
Top view of PCB with lid removed, note the red button stands above the PCB mounted on standoffs.
Underside of the PCB, I used 3mm nuts to space the bottom of the PCB from the bottom of the box