Can anyone measure the value of an inductor?

Paully · 8793

0 Members and 1 Guest are viewing this topic.

Offline Lee Hankins

  • Full Member
  • ***
    • Posts: 165
Reply #15 on: January 21, 2011, 12:04:57 PM
Jim, thank you for the reply.  The way Paully started out this Post and the responses he was getting I just thought that I was missing something or doing something wrong.  Most newer DMM's seem to include an inductance range so why would one consider sending out the inductors, freight would cost more than an inductance meter.

Lee Hankins

Lee Hankins
"End of the Road"
Homer, Alaska


Offline JC

  • Sr. Member
  • ****
    • Posts: 485
Reply #16 on: January 21, 2011, 12:27:15 PM
Well, I can't say that I have much experience with the inductance-measuring feature on newer meters; I certainly don't own one with that feature, but I can sure see how it would come in handy. 
 
Seeing these responses and links, to me, reinforces the idea that measuring inductance is considerably more complex than, say, measuring resistance or Voltage.  In my mind, anyway, the meter would have to be generating an AC test signal, measuring some aspect of how the inductor reacts to the frequency it is generating, then translating that into a useful reading on the display!  Quite a bit of math going on there, among other things!

Jim C.


Offline Paul Joppa

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 5833
Reply #17 on: January 21, 2011, 01:01:56 PM
Man, I had a beautiful and very long-winded answer, which failed to post and I lost it!

Oh well. The fact is, an inductor with an iron core will have an impedance that is partly inductive, partly resistive, and partly non-linear (hysteresis losses). And these will vary with frequency and signal level. (And at high frequencies, capacitances will mask inductive behavior making measurements impossible.

For crossover applications, the best practical thing is to measure the series resistance, the inductance, and the parallel "resistance" at a frequency near the crossover frequency and at a signal level near that expected in use. For this you need a bridge that works with an external oscillator, and of course the external oscillator. These buggers are difficult to use. I don't have one.

Paul Joppa


Offline Grainger49

  • Hero Member
  • *****
    • Posts: 7175
Reply #18 on: January 22, 2011, 02:15:07 AM
elcraigo,

The Monster power supply got stalled.  Trouble in the high voltage supply side.  That and cutting and changing the feed to the C4S board for dual mono feed.  I hate to take my Seduction out of the system to butcher it while it sounds so good.

I will do it soon, I keep saying that but will.
« Last Edit: January 22, 2011, 02:21:09 AM by Grainger49 »



Offline Paully

  • Sr. Member
  • ****
    • Posts: 516
Reply #19 on: January 22, 2011, 09:08:18 AM
I am really, really happy with the sound of the speakers from what I have heard to this point.  Ecstatic actually.  But I don't need to be able to measure inductors multiple times (though I appreciate the suggestion, it was neat).  I just want to know what it is for these one time since I probably am not going to become a crossover engineer (anyone who is familiar with my posts knows that isn't going to be a serious problem for me anytime in the near future).  Postage back and forth is pretty much all I want to incur.  So Jim, if you will send your address to me and you don't mind sending them back at my expense, I would love to know how close the inductors are that I took out to the schematic that is on the web that everyone seems to be using.  I know there is a lot more to it, but I still would like to see if they measure close to the stated 3.5mh.  I appreciate the offer, thank you!

And Jim, you may not be interested, it sounds like you know plenty about what you have planned for your speakers, but when I upgraded my Klipsch crossovers for my Chorus II using Bob Crites' I was pretty pleased.
« Last Edit: January 22, 2011, 11:17:50 AM by Paully »



Offline johnsonad

  • Hero Member
  • *****
    • Posts: 1670
Reply #20 on: January 22, 2011, 02:36:32 PM
Paul, congrats on the rebuild.  I'm in the process of building new crossovers for my Model 19's.  I've got a handheld LCR meter and was astounded by how much my inductors were off by, a couple as much as 25%!  The caps were even worse at up to 50%.  No wonder I've needed a balance control on my preamp...  I went all out and picked up North Creek inductors and all of the caps and resistors are within 1% matching.   

I'm waiting on speaker wire to build the crossovers and plan on burning them in with my Paramounts once the soft start kits come out before putting them into the speaker.  My to do list includes Dynamat for the horns, internal bracing and resealing the cabs.  Hopefully my results are as good as yours!

Aaron Johnson


Offline Jim R.

  • Hero Member
  • *****
    • Posts: 2194
  • Blind Bottlehead
Reply #21 on: January 24, 2011, 02:29:13 PM
Paul,

Sent you a PM the other day.  Haven't heard from you so don't know if you saw it.

-- Jim

Jim Rebman -- recovering audiophile

Equitech balanced power; uRendu, USB processor -> Musette DAC -> 5670 tube buffer -> Finale Audio F138 FFX -> Cain and Cain Abbys near-field).

s.e.x. 2.1 under construction.  Want list: Stereomour II

All ICs homemade (speaker and power next)


Offline Grainger49

  • Hero Member
  • *****
    • Posts: 7175
Reply #22 on: January 25, 2011, 01:25:48 AM
Paul may not have turned on email notification for PMs.  I sent him an email.
« Last Edit: January 28, 2011, 06:31:34 AM by Grainger49 »



Offline Paully

  • Sr. Member
  • ****
    • Posts: 516
Reply #23 on: January 28, 2011, 06:16:03 AM
"I've got a handheld LCR meter and was astounded by how much my inductors were off by, a couple as much as 25%!"

I am really surprised by that, one, because all of the parts in my speakers were still within 10% and also I wouldn't have thought that an inductor would drift all that much.  I guess I think of them as little transformers where the winding is what matters and that shouldn't age so much.  But I also don't know that much about inductors!  Just curious what would cause an inductor to drift over time or is it possible that, just like the 846A, they changed the crossover values here and there with the Model 19 while tweaking and didn't publish it.  That was why I was so curious to measure the value of my inductors.  I have read that this specific crossover for the 846A is often found with widely varying values that have nothing to do with drift, so I wanted to know if mine matched up to the schematic or not.



Offline elcraigo

  • Full Member
  • ***
    • Posts: 107
Reply #24 on: January 28, 2011, 09:16:11 AM
Depends on the Inductor
I've seen inductor specs from -30 /+50% to +/- 3%

Craig Lewis (elcraigo is a nickname a good friend who grew up in Mexico gave me)


Offline Paul Joppa

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 5833
Reply #25 on: January 28, 2011, 10:47:41 AM
Inductors don't drift, but their measured value (if they have a non-air core) will vary with frequency and measuring current. And with exactly what is measured, since the terminal impedance is a combination of several things with different phase angles - some measurements sort these out differently from other measurements. The long-winded answer I wrote, which got lost (see my previous post) went into excruciating detail - probably a good thing it was lost!

Bottom line, never trust an inductance measurement unless you know an awful lot about it and the device being measured! I have a simple-minded choke checker which I use for plate and power supply chokes, and it regularly reads 10% to 30% lower than proper, carefully made measurements done with good instruments. Since I expect that error and have confirmed that it is always with that range of error, it's still useful to me - but it's sure not accurate!

Paul Joppa


Offline johnsonad

  • Hero Member
  • *****
    • Posts: 1670
Reply #26 on: January 28, 2011, 12:53:37 PM
As PJ said, I don't have the right tool ;)

I read somewhere that the tolerances with the Altecs was lower than 10%.  For some reason 25% comes to mind but I'm probably wrong on that too....

Aaron Johnson


Offline Jim R.

  • Hero Member
  • *****
    • Posts: 2194
  • Blind Bottlehead
Reply #27 on: February 04, 2011, 04:57:59 AM
Paul,

YGPM, and your inductors will be on the way back to you today.

-- Jim


Jim Rebman -- recovering audiophile

Equitech balanced power; uRendu, USB processor -> Musette DAC -> 5670 tube buffer -> Finale Audio F138 FFX -> Cain and Cain Abbys near-field).

s.e.x. 2.1 under construction.  Want list: Stereomour II

All ICs homemade (speaker and power next)


Offline Grainger49

  • Hero Member
  • *****
    • Posts: 7175
Reply #28 on: February 04, 2011, 05:13:55 AM
As PJ said, I don't have the right tool ;)

I read somewhere that the tolerances with the Altecs was lower than 10%.  For some reason 25% comes to mind but I'm probably wrong on that too....


I got the results from Paul.  They are low by about 25%.  I think you got it right.



Offline Jim R.

  • Hero Member
  • *****
    • Posts: 2194
  • Blind Bottlehead
Reply #29 on: February 04, 2011, 05:25:42 AM
Grainger,

Yes, they are low, but at least they are quite close to each other.  I ran the test many times on each and got very consistent results.

I had been thinking of selling this little gadget and the software, but no way I'm doing that now -- this thing is just too cool.  I'm going to have to ressurect mycritical headphone cable project.

-- Jim

Jim Rebman -- recovering audiophile

Equitech balanced power; uRendu, USB processor -> Musette DAC -> 5670 tube buffer -> Finale Audio F138 FFX -> Cain and Cain Abbys near-field).

s.e.x. 2.1 under construction.  Want list: Stereomour II

All ICs homemade (speaker and power next)