# Thread: Inductance meter?

1. ## Inductance meter?

Does anyone know how to easily test inductance or make an easy inductance meter? I ripped a bunch of inductors out of an old PSU but I have no idea what their values are.

2. shoot me a email i got a file i can send you with schematics and pcb layout of a inductance adapter for you dmm

3. Thanks, I posted a link to it here.

A little more complicated than I was hoping, however.

4. ## Re: Inductance meter?

Originally posted by Telek
Does anyone know how to easily test inductance or make an easy inductance meter? I ripped a bunch of inductors out of an old PSU but I have no idea what their values are.

5. \$130?! Yikes!

I was thinking something along the line of a simple high-resolution timing chip with a voltage sensor (maybe a pic solution) where you pop it in, it'll run power through it and time how long it takes to charge and discharge, and give you a reading based on that. Or something simple that can measure the inductance based on the amount of current that it takes to maintain the inductor, or some circuit that will find an inductance reading and create a voltage so that you can use a voltmeter to read it, or something. Seems like a rather simple thing to do, but I haven't found any really simple solutions

Thanks anyway thou.

6. I built a project like this for a Senior Lab to determine inductance in a large coil. A small coil should be the same thing.

You'd need a voltage supply, an oscilliscope, and a switching mecaninsm (like a pnp transistor), a square singal generator, and a discharge load (resistors).

Basically you wire up the scope to watch how the coil charges up and charges down as the transistor switches on and off the supply in time with the signal generator. The coil will show a typical exponential decay curve, and from that you can determine the inductance.

The point is to take the time off the scope that the value of the voltage reaches half the maximum. Since the decay value is one-half the time, the equation is :

1/2 E/R = E/R (1-e^(-t/T)) T being the decay time constant:

E = voltage

R = discharge resistance (in Ohms)

T=L/R (L is indictance in Henrys).

So, t = T ln 2 --> Ln 2 t/R = L

I'll see if I can't post a schematic tomorrow.

7. I built the circuit in that magizine article and it works pretty well. It helped me when I was learning how to build the MPSB1. You should be able to find it in a kit form. I built it up on a bread board and it worked. It is basically just charging up a cap with a square wave and based on the inductance, the voltage across the cap goes to some value that is linearly proportional to the inductance. You can use an HC14 instead of the Nand gate. They are just using it as an inverter anyway..

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