Inductance meter

[rasco22862]

Is there any schematic or layout of a inductive meter for wah wahs inductors?

[Seljer]

Is there any schematic or layout of a inductive meter for wah wahs inductors?

I've seen many microcontroller inductance/capacitence meter projects
http://www.google.com/search?hl=en&safe=active&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=microcontroller+inductance+meter&spell=1


edit: seems like there are plenty of simpler ones out there too, range and accuracy varies though
http://www.google.com/search?hl=en&q=inductance+meter+schematic&btnG=Google+Search

or you could just creat a bandpass filter/band stop filter (inductor+capacitor), with a know value for the capacitor (estimate the value of the inductor then choose a capacitor so it ends up in the audible range), then with a signal generator, sweep the frequency until you find the centre of the filter band, with the frequency and the capacitance you can do the math to figure out the value of the inductor

[rasco22862]

yes, but those one don´t measure more than 100 millihenries, and the wah wah has a 500 milihenries inductor

[Daniel]

? why won't they measure more than 100mH? i think they could... don't see why not hehehe =]

another thing u could do if u're accuracy is not THAT importante to you is doing a voltage divider, just remember de DC resistence of the coil so the results will be more accurate... i've done this method a few times cause it's really simple, but I can't tell how accurate it is as I didn't have any inductors with know values available but the results where close to what i expected =]

[brett]

If you've got a sine-wave generator and either a scope or good DMM, you can easily measure inductances. 
My sine-wave generator is nothing fancy (a US$15 kit based on an LM13600) but it works fine.
I've measured inductances from about 0.1 mH to 5,000 mH this way.  The accuracy is not that good, but repeatability is very good, so if you calibrate against a known inductance, you can expect good precision.

The schematic is:



The method:
1.  Set the sine wave generator to at least 1 volt p-p, and the scope to a similar range.
2.  Select a suitable capacitor (C) for the likely inductance.  0.1uF is useful for 1 to 100 mH, and 0.01 is useful for 100 to 10,000 mH.

If the inductance is higher or lower than 1 mH and 10,000 mH, use this equation:

C = 1/(L.(2.pi.f)2) 

where C is the capacitance (Farads), L is the inductance (Henries), pi = 3.14 and f is the desired frequency (Hz).  About 1 kHz is often a good value for f.

3.  Sweep the frequency of the sine waves up and down.  The amplitude of the signal will vary with frequency, especially within a particular band of frequencies.

4.  As closely as possible, note the frequency at which the amplitude peaks, then use the following equation:

L = 1/(C.(2.pi.f)2) 

Note:
It is easy to make up a chart(s) of frequency vs inductance for different values of C.  This saves messing with formulae.

Any DMM should also be able to measure the amplitude of the signal (ie a scope isn't needed), but in that case the peak frequency must be indicated on either the DMM or the signal generator.

[Rob Strand]

For infrequent measurements, methods like brett gave are far more reliable.

BTW, (2.pi.f)2  is (2.pi.f) squared.

Many inductance meters suck, they don't work, that goes for a lot of commercial stuff too.
- DC resistance and losses make measurements inaccurate
- Sometimes external humm affects the measurement.
- only measure large inductances