inductance test frequency

[Rosewood]

My didgital vom test inductance at 200 hz, is that usful at all and if not why. I seem to recall testing at 500 to 1k was what was needed but I can't remeber why.

[Joe Gwinn]

My didgital vom test inductance at 200 hz, is that usful at all and if not why. I seem to recall testing at 500 to 1k was what was needed but I can't remember why.

Inductance measured at 200 Hz isn't useless, but inductance measured at 1,000 Hz is far more useful for audio components such as guitar pickups.

A bigger issue is if your meter is able to accurately measure the inductance of low-Q inductors such as pickups. Many LCR meters fail miserably here, being off by a large factor, yielding claimed inductance values that are unrelated to reality.

What make and model of meter are you using?

[Rosewood]

Hi Joe, the meter is a elenco lcm 1950. This may be reaching a little too far but say you have a pickup with a published inductance value, could you measure that at 200hz and get any good information knowing what the published specs were?

[belwar]

Pardon my ignorance if I get this wrong, im still learning.

Having only one test frequency isn't going to let you test the accuracy of someone elses inductance measurement unless they tested at 200hz. Inductance changes with the frequency that it is tested at.

For example, I tested a P-90 that I made the other day... At 120hz I got a measurement of 6.78, but at 1000hz I got 22.71 (rounded for accuracy).

The unloaded resonance freq was 6.22.

... and the pickup sounded like crap. Switched to A5 from A4 and it sounded like a dream.

[salvarsan]

For example, I tested a P-90 that I made the other day... At 120hz I got a measurement of 6.78, but at 1000hz I got 22.71 (rounded for accuracy).

Test for serial, not parallel inductance using the Extech. That's what the SER/PAL button is for.

120Hz and 1kHz inductance readings should agree within 10% then.
Usually, the 1kHz L is lower than the 120Hz L.

The unloaded resonance freq was 6.22.

... and the pickup sounded like crap. Switched to A5 from A4 and it sounded like a dream.

The LCR meter readings are unrelated to sound quality -- they tell you details about the consistency of your batch of pickups.

-drh

[Rosewood]

Test for serial, not parallel inductance using the Extech. That's what the SER/PAL button is for.

120Hz and 1kHz inductance readings should agree within 10% then.
Usually, the 1kHz L is lower than the 120Hz L.


The LCR meter readings are unrelated to sound quality -- they tell you details about the consistency of your batch of pickups.

-drh

Are you saying the inductance value at 120hz and 1k should measure within 10% of each other? If that's so should it be within 10% at 200hz also?

[salvarsan]

Are you saying the inductance value at 120hz and 1k should measure within 10% of each other? If that's so should it be within 10% at 200hz also?

For a given pickup type and using the serial mode on the Extech LCR meter, YES.

An SK P-90 at hand measures
7.4H@120Hz and 7.0H@1kHz in SERial mode, but reads
22.5H@120Hz and 7.7H@1kHz in PARallel mode.

The parallel readings don't seem useful here.

Inductance means that the coil impedance decreases linearly with frequency
...until distributed capacitance and eddy current effects become significant.

Otherwise, the pickup impedance plot would be a flat sloped line instead of a curved one, like below:

[Mike Sulzer]

An SK P-90 at hand measures
7.4H@120Hz and 7.0H@1kHz in SERial mode, but reads
22.5H@120Hz and 7.7H@1kHz in PARallel mode.

The parallel readings don't seem useful here.

Well, that makes sense; the resistance of the coil does appear in series with the inductance. Losses due to eddy currents appear as a resistor in parallel. Can we be sure that eddy losses are very small at low frequencies? Because the meter cannot handle both series and parallel resistances. You cannot get three derived parameters from two numbers.

I think the only way to be sure is to make measurements over a range of frequencies and then compare these measurements to a model of the pickup circuit containing all significant effects. This is not so easy.

[RedHouse]

For a given pickup type and using the serial mode on the Extech LCR meter, YES.

An SK P-90 at hand measures
7.4H@120Hz and 7.0H@1kHz in SERial mode, but reads
22.5H@120Hz and 7.7H@1kHz in PARallel mode.

The parallel readings don't seem useful here.

Inductance means that the coil impedance decreases linearly with frequency
...until distributed capacitance and eddy current effects become significant.

Otherwise, the pickup impedance plot would be a flat sloped line instead of a curved one, like below:

What software is that in the pic?

[salvarsan]

What software is that in the pic?

It comes bundled with a fancy hardware dongle for ~$190:
http://www.syscompdesign.com/circuitgear.htm


The device is a hobbyist/student-grade digital scope + signal generator.

-drh

[David Schwab]

It comes bundled with a fancy hardware dongle for ~$190:
http://www.syscompdesign.com/circuitgear.htm


The device is a hobbyist/student-grade digital scope + signal generator.

I've been wanting to pick up a 'scope. That looks pretty cool. So do you like the software?

Dongles... Already have two dongles on my Mac... I'm going to need a separate USB hub just for the dongles soon!

[salvarsan]

I've been wanting to pick up a 'scope. That looks pretty cool. So do you like the software?

It's a good enough. It is also open source and cross-platform.

Dongles... Already have two dongles on my Mac... I'm going to need a separate USB hub just for the dongles soon!

My joke -- the device itself, whatever its functionality, is by definition a dongle since the software doesn't do anything without it.


-drh

[Joe Gwinn]

Hi Joe, the meter is a elenco lcm 1950. This may be reaching a little too far but say you have a pickup with a published inductance value, could you measure that at 200hz and get any good information knowing what the published specs were?

The first question to ask is if the Elenco LCM 1950 can make a valid inductance measurement on a guitar pickup. If not, the rest of the question is meaningless. So, first we must see if the 1650 is up to the job. Most ~$200 LCR meters are not. The Extech is one LCR meter that is known to work.

[David Schwab]

My joke -- the device itself, whatever its functionality, is by definition a dongle since the software doesn't do anything without it.

That's a common term though... I have two USB dongles plugged into my keyboard's USB ports, one for Cubase SX and the other for Pro Tools. I have cordless mouse so I don't need those ports, but if I get a new dongle I'll have to stick it in the USB 2 card I have installed, or get a spare hub, which is funny, since they don't do anything on their own.

I guess the proper term is "hardware key", but I've always called them "dongles".

[Joe Gwinn]

My didgital vom test inductance at 200 hz, is that usful at all and if not why. I seem to recall testing at 500 to 1k was what was needed but I can't remember why.

You might try the test described in the following ancient posting: http://music-electronics-forum.com/s...1&postcount=20.