Measuring inductors

[hodad]

I have one of those cheap LCR/Transistor testers (like this: tester), and when checking inductance across one side of a transformer I get a different reading depending on which pair of the 3 connections on the meter I use. As a f'rinstance, I'll see 2.4 Henries if I'm hooked to 1 & 2, but 3.8 across connections 2 & 3. I'm a little befuddled as to what would cause this difference. The meter, considering its cheapness, has proven pretty useful in other situations, and I can't quite figure out why I'm seeing what I'm seeing here.

 

[emrr]

Is it series / parallel?

 

[gyraf]

To figure out what terminals are closest to the truth, put a known-value capacitor in series and measure resonant frequency..

 

[CJ]

What kind of transformer are you trying to measure?

 

[hodad]

What kind of transformer are you trying to measure?

Just a crappy little 600:600 OEP. I've also tried with another small isolation transformer of unknown origin with similar results. Measuring across either primary or secondary produces similar results. I'll probable just build a couple of simple filter circuits & see which value seems best reflected by the behavior I see.

 

[CJ]

How come they have 3 leads on the tester?

 

[Gold]

How come they have 3 leads on the tester?

It does transistors too. It's a very handy little tester. You can also get them in a small case with an Li battery for more like $18.

 

[dai h.]

(I think) those are from this open source project:

https://www.mikrocontroller.net/articles/AVR_Transistortester

FWIW (instructions on measuring coils) is on page 45 "section 3.10 Measurement of coils"

https://www.mikrocontroller.net/articles/AVR_Transistortester#Downloads_(English)

 

[hodad]

Apparently it struggles with measuring inductance across a transformer. The manual is not terribly clear on whether it has trouble with all inductors over 1H or not. It does seem to work fine with smaller value inductors though.

 

[dai h.]

FWIW I vaguely recall (on another forum to do with discussing (guitar, bass, etc.) pickups that some LCR meters have trouble measuring L when the R is (relatively?--not sure exactly how much) high. I was rather disappointed with my (IIRC) A&D 5827(?) LCR meter which was kind of expensive for occasional hobbyist use (it was only after I bought it that I found many of the pickup winding people seemed to be primarily using another model (which I forget the name of) which apparently did work for measuring pickups (and was less expensive than the one I purchased, to boot).

After that a parts seller/store (here in Japan) started selling the (Taiwan made) DE-5000 (from 2012 according to the web page) and did one of those "mass purchase (10,000 units initially according to their FAQ) and pass the cost savings to the consumer" type deals (maybe USD$50-ish at the time for the unit only without the accessories (which were also very reasonably priced--credit to them), and those apparently are okay to measure pickups with--which I bought since the price seemed too good to pass up on. (Those are the ones on ebay coming from various individuals from Japan with the Japanese text on the box--unfortunately the price has gone up since they apparently pay in USD and the Yen has weakened vs. the dollar a lot--took a quick look and they are about USD$61 for the unit only, so still not very expensive, however since they don't ship internationally I guess you have to buy from some intermediary if you want one.) Anyway, perhaps there is something better now (I haven't really kept up with the latest available).

 

[S.Samuelsson]

Hi.

(I think) those are from this open source project:

https://www.mikrocontroller.net/articles/AVR_Transistortester

Yes... and no.

There are several far east manufacturers that have based their versions of that particular microcontroller based tester on the Frejek/Kübbeler work, but the more one reads about it, the more apparent it becomes that a lot of corners have been cut on the far east offerings.
Not surprising at all considering the price those testers are offered.

There are also alleged differences between the manufacturers as well.
I have two different ones from completely different sources, and while the values measured are similar enough to be useful between those two, there are differences.
The PCB's are similar, but not the same.
IDK about the circuitry, but I'd assume that there's differences in there as well.
As there are probably in the firmwares as well.
The beotch of it is the fact that it's almost impossible to find out what particular manufacturer has followed the original work the closest, so buying one of the far east offerings is a roll of dice.
But a cheap one at that .

AFAIK there are quite a few individuals that assemble, test and sell those testers in the west as well, but the price is obviously something entirely different.
And as per the original idea behind that project, there's always the DIY route.

Whether those aforementioned differences matter in the real world, that's a different topic.
And also something that everyone has to decide for themselves.

FWIW (instructions on measuring coils) is on page 45 "section 3.10 Measurement of coils"

https://www.mikrocontroller.net/articles/AVR_Transistortester#Downloads_(English)

Those instructions are as good as any place to start, but not all of them are accurate on the clones.

Regards,
Sam