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Old 23rd October 2009, 12:57 PM   #11
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My 2 cents -- I use a GR 1658 Digibridge AND a Heath IB5281 manual bridge. You can often find the latter for less than $10 and it's accurate within a few percent.

I had an HP which was very nice, but gave it to the University.

I have been tooling around with the Analog Devices impedance analyzers on a chip -- these babies are remarkable since you can sweep a frequency range with them. You can thus make Q measurements as well.
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Old 23rd October 2009, 02:42 PM   #12
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by Allen Wright View Post
I don't know why you guys are heaping dirt oncheap DMMs - I suspect you have never tested them. As I stated, our two cheap (circa $50) DMMs are both within 1% of my GR digital bridge (which wasn't $50!!) on the ranges needed for crossover chokes.
You said most of the relevant things: this kind of instrument can indeed measure inductances whose minor parameters are negligible and values not too extreme. Under those conditions, the accuracy will be that of the calibration, and can be pretty good.
But when you attempt measuring inductances of lowish values, having high losses, things don't go that smoothly.
Measuring the leakage inductance of a transformer with these instruments gives fancy results, because the minor parameters at the test frequency are overwhelming and cannot be resolved from the true inductance.

But, OK, for crossover coils, it is probably sufficient.
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Old 23rd October 2009, 07:15 PM   #13
ro9397 is offline ro9397  United States
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In the imortal words of L.A. "motorist" Rodney King, "Can't we all just get along?"...just kidding!

Thanks for the helpful & timely replies. I'm leaning toward just following the specs from an online inductance winding calculator. If I get a meter it will be the above mentioned $45 LC from PE. Too bad the MM adapter instructions are in French.

Thanks again!

Decades ago when cosmetics were low priority speaker projects came together quickly. Now I'm getting older & sweating every detail. This may be my last hurrah in a reference speaker so it's going slow & easy, even though only the xo & final assembly remains to be completed.

OT: The panel laminate is 5/8" real Russian BB ply (5x5 sheets, no voids, many fine layers) over 5/8" old-fashion particle board; each panel was individually laminated. Recommended A+.
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Last edited by ro9397; 23rd October 2009 at 07:24 PM.
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Old 23rd October 2009, 07:32 PM   #14
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Since you are going to build a 2-way speaker system I think that the WT3 Woofer Tester from Parts-Express would be an excellent choice.

You can use it for checking you driver´s impedance, you can measure inductors and resistors. Furthermore, it works fast (!) and it is a breeze to use when designing your zobels and notch circuits. It measures your speaker or circuit within 2-3 seconds.

It is not stated in the tech. papers but the WT3 can easily measure small inductors. Expect the tolerances to be within 5% when calibrated with a 1 % resistor (delivered together with the WT3). For values below 0,5 mH the error might increase, though. Precision when measuring resistors will be approx. +/- 0,25 % when calibrated with the 1000 Ohm 1% resistor.

Right now the WT3 is delivered together with a small precision scale. This can be used if you are going to make your own T-S parameters (Vas) with the "added mass method".

I tested my precision scale since I was a bit sceptical about this cheap little device. I could not get my hands on some extremely precise reference weights but used some coins with a well-known weight. The precision scale showed the weight spot-on in approx. 75 % of the cases. The rest 25 % was extremely close.

You can see it all here:

Parts-Express.com:*Dayton WT3 Bundled with Precision Scale | parameter testing speaker speaker tester woofer tester woofer tester 2 woofer tester 3 wt2 wt3 www.woofertester.com woofertester.com woofertester3 woofertester2 clio lms linearx melissa mls

Karsten
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Old 23rd October 2009, 08:13 PM   #15
dangus is offline dangus  Canada
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Any speaker testing software that can measure impedance ought to be able to measure inductors. Like "speaker workshop"; it says it can measure "passive components".

The self-calibrating L/C meter project in the June 1996 "Electronics Now" is about the simplest meter possible, if you'd rather build. There's a PIC, a comparator, a common alphanumeric LCD, and not much else. However, one big problem that I just noticed (after digging up the original magazine issue): it doesn't go up into the millihenries or over one uF, which makes it nearly useless for audio diy. Check the clones and updated versions carefully; I'm sure someone has modified it for a wider range by now. There's versions that use Atmel mcus instead, and even one that reads out in Morse code so you can measure things in the dark.

Here's what I posted before:
Quote:
Originally Posted by dangus View Post
The PIC meter from AlmostAllDigitalElectronics (AADE) was published in June/96 Electronics Now, and hex was available from the Gernsback website (or BBS) at one time. LC PIC meter has hex code, and links to many other PIC L/C meter pages.

I found a partial mirror of the Electronics Now ftp site, and here's the schematic and assembler and hex for the L/C Meter II.
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Old 23rd October 2009, 08:52 PM   #16
anatech is offline anatech  Canada
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Hi Conrad,
Quote:
...if you have a scope and generator, resonate the inductor with a known cap, then calculate the value from the frequency
Exactly. Accurate and easy requiring gear that most of us have on the bench.

I've even seen projects using a 555 timer, but these and meters generally only make the reading easier to take and often will be off a little.

Hi Jack,
Quote:
I use a GR 1658 Digibridge
Nice!
Quote:
I had an HP which was very nice, but gave it to the University.
Big tears!!
I had an HP 4261A that I liked a lot (still at my old shop), it would also measure transformers. I miss it for that reason. My newer 4263A doesn't have the transformer option, but otherwise I really love that thing. Of course, now I have the need for testing components at 10 MHz and up. Out of range for the 4363A, and Ebay offerings for those types are still very, very high. The one thing the meter makes real easy is "Q" factor, or dissipation depending on how you set it up.

Jack, have you actually got one of those Analog Devices chips running now? I'd be interested in your construction if you have. I have loudspeaker driver testing in mind. It takes me 20 minutes or so with my TI calculator and normal bench gear. At least my numbers are accurate.

Hi ro9397,
From what you have said so far, I'd still recommend you resonate the inductor with a known capacitance. You probably have everything you need on hand for that. It's a no cost option. Failing that, a Heathkit impedance bridge would do very nicely and at low cost. I'll bet it's more accurate than many digital instruments out there.

The one thing I tend to see is that the average person assumes greater accuracy from a digital display, completely unfounded of course. Measuring reactive components seems to be much less accurate than a pure resistance. Often times, the last two digits on a less expensive digital meter are not useful once you figure out the error budget. Of course, that's an answer that not many people wish to see (or even know about).

Good luck on this no matter which way you end up going.

-Chris
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Old 23rd October 2009, 10:43 PM   #17
dangus is offline dangus  Canada
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The version of the AADE L/C meter I linked to (LC PIC meter) does have an enhanced range compared to the original: "1 nH to 150 mH, 0.01 pF to 10 uF"
The morse code version ELSIE Meter Kit (which also has serial port interface, and LED option, and measures frequency), measures even higher L:
"Capacitance: ~ 1 pF to ~ 1 uF
Inductance: 1 uH to ~ 500 mH
Frequency: up to 40 MHz (in version 2 software)"

Still, computers with sound cards are cheaper than the parts to build such a meter, and if you're reading this, it's reasonably likely that you already have one. Using free software, they can measure complex impedance at the push of a mouse button. Getting the same results from basic bench instruments still requires a calculator or spreadsheet - or logarithm tables or a sliderule, for the real traditionalists.
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Old 23rd October 2009, 11:28 PM   #18
dangus is offline dangus  Canada
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[ran out of time while editing my previous post]
I'm not in a hurry to get rid of the vintage General Radio impedance bridge, but I'm an idiot not to have made room on the test bench for a tiny PC with IMP/M or "Speaker Workshop". My excuse is not yet building up an interface box with built-in test amplifier, and how much space a CRT monitor would hog. It's not that I believe that demons live inside computers and they are gateways to hell (to paraphrase a Hellraiser movie), as you might suspect. In fact, if software existed, a dedicated PC could get by with a parallel-port (or serial) alphanumeric LCD display, and just a few buttons on a keypad or game controller. Using a "biscuit pc", 1/2 ISA, PC/104 or other embedded computer board, it could fit in an old bench-top instrument case.

Here's an Elektor article on a simple soundcard RLC meter; software can allegedly be downloaded from Elektor (June 2008).
http://icom.hsr.ch/uploads/media/RLC_Meter_EN_01.pdf The hardware required is a couple of opamps to buffer the sound card inputs, and a reference resistor.

The same search terms turned up Tor Vergata's impressive "Visual Analyzer" project, which interestingly requires exactly the same hardware: ZRLC (It also does 'scope, spectrum analyzer, function generator, and much more.)

Last edited by dangus; 23rd October 2009 at 11:42 PM.
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Old 23rd October 2009, 11:35 PM   #19
anatech is offline anatech  Canada
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Hi dangus,
Thanks. I'll look into these things.

I have to admit that I'm slow at adopting sound cards for bench use. Computer connections can create odd problems at times.

-Chris
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Old 24th October 2009, 01:50 AM   #20
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Quote:
Originally Posted by anatech View Post
Jack, have you actually got one of those Analog Devices chips running now? I'd be interested in your construction if you have. I have loudspeaker driver testing in mind. It takes me 20 minutes or so with my TI calculator and normal bench gear. At least my numbers are accurate.
Yes, I have used it -- but I don't think that the low impedance accuracy is adequate for speakers -- on the other hand, if you had to measure the corrosion in the karzi of an Airbus A320 (or something aluminum like that) it would work like a champ -- and this latter problem has been driving the folks in Toulouse nuts. Problem is that you'd have to add series resistance, etc., etc.
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