UTC 0-15 Inductance data (was Maxwell-Wien Bridge)

I checked the spec's on my Fluke 79 III, and I see it will work from

45Hz to 1kHz. So now I believe I might be able to get a reliable measurement. The down side is it has a 100pf input impedance, along with the 10 megaohms resistance. I plan a 1 meg resistor in series with the input to the meter to keep the 100pf from being in parallel with the coil. Anyone see a problem with that, is there a better solution?

Mikek

If you would put the problem in LTspice, you might see the problem a bit better.

As I can see this issue is leading nowhere, I'm afraid I will be unable to spare the time to contribute further. Good Luck!

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There seems to be an arithmetic error the last line. If I run those numbers I get 2712 Henries. I suspect the 279Hz number.

It's low, but if the windings were configured for low inter-winding capacit ance - built up as a number of banks of layers, rather than a single bank w ith each layer wound directly above its predecessor - it might be feasible.

If there are x layers, and the interlayer capacitance is y pF, then the par allel capacitancer is y/x pF.

By breaking the winding up into n banks, the interlayer capacitance reduce to roughly y/n and there are n more layers, so the parallel capacitance is reduced by n^2. The winding space wasted by the bits of the former that sep arate the banks screws up the actual numbers a bit, but that captures the g eneral idea.

The extreme case is to wind the coil as a series of pancakes, each bank bei ng just one wire thick, which throws away half your winding space and force s you to think about the inter-pancake capacitances ...

--
Bill Sloman, Sydney

** SNIPPED due to aioe *

May i Pete again (Re-Pete)? Ditch the C, use 10Hz, make all arms about the same Z like i said. Maxwell will be happy.

** SNIPPED due to aioe **

capacitance - built up as a number of banks of layers, rather than a single bank with each layer wound directly above its predecessor - it might be feasible.

parallel capacitancer is y/x pF.

reduce to roughly y/n and there are n more layers, so the parallel capacitance is reduced by n^2. The winding space wasted by the bits of the former that separate the banks screws up the actual numbers a bit, but that captures the general idea.

bank being just one wire thick, which throws away half your winding space and forces you to think about the inter-pancake capacitances ...

With or without the maple syrup?

Lemon juice is better. I've seen liqueurs used, but my head felt fine the following morning, and the liqueur-fanciers all had horrible hang-overs.

But anybody silly enough to confuse pancake windings with crepes won't be too well-informed about food either.

--
Bill Sloman, Sydney

Mike, I'm having trouble understanding all this.

The UTC site says that the O-15 has the following characteristics:

Interstage plate-to-grid transformer with 15k to 1Meg impedance transformation. 100-3000 Hz +/- response within 1dB. 8dBm max (6.3mW) and 330 ohms primary resistance.

Are you trying to measure the primary or secondary inductance?

Where are you getting the resistance values? Please use an ohmmeter to measure the resistance of the primary winding and secondary winding.

What is it that you want to know about this component?

If it is a plate-to-grid transformer, it cannot be very intolerant for DC on the plate side. In a normal circuit, the DC plate current is intended to flow via the primary.

--

-TV

I'm trying to find the inductance of the 1 Megaohm winding. Last night I used this set up.

Wired on my Fluke 79 III like this.

So I adjusted frequency for a null at resonance.

Feel free to criticize the method, that's why I'm here.

I used three capacitance values 60pf, 90pf, and 180pf. I tested a three different currents, I got a range of 1515 Henries to 1739 Henries. This does not factor out the distributed capacitance. The inductance went up at the lowest test frequency 278Hz. The other frequencies were 425Hz and 530Hz. I may be getting close.

It has been suggested that I measure the 15K winding and extrapolate to the 1 Meg.

I don't want to apply DC to my windings, but others have, 4,875 ohms and 330 ohms are in the ballpark as the manufacturer lists.

Again, this is for pleasure and knowledge. This started when I became aware I have some large ferrite potcores with an A sub L that with

10,000 turns will have over 3 Mega ohms of impedance at 300Hz. Meaning I could wind a matching transformer. The core will hold about 18,000 turns of #36 wire. I have a UTC 0-15 that is spec'd at 1 Meg to 15k. Then the question came up what does 1 Meg mean, or rather does it follow the 4 times rule. (If it follows the 4 times rule, then it should have 4 megaohms of impeadance at 300Hz.) If the UTC follows the 4 times rule then the 1 meg winding should have 2123 henries of inductance. Again for pleasure and knowledge. Mikek

I started with a question about a transformer, the UTC 0-15. Does this design follow the 4 times rule as detailed here;

The article concludes with, "We have shown that the ?four times the impedance? design guideline for the inductive reactance of the transformer windings yields an impedance transformation that departs from its ?ideal? behavior by no more than

3%, and introduces a phase shift of no more than 14 degrees."

It is spec'd at 1 Meg to 15 k, with 80Hz to 3000Hz -3db points. Looking at the frequency response graph for the UTC 0-15 transformer.

I pick 350 Hz as the point where it falls below the 3% criteria. Why, because I don't know any better. It's a WAG. Using 120pf to get resonance at 293 Hz test, I calculate 1715 Henries of inductance for the 1 Meg winding. At 350 Hz, 1715 Henries calculates to

3.77 Megaohms. Close to 4 times.

One thing I have not accounted for is the distributed capacitance of the winding, I think this makes the inductor measure larger? than the true inductance. Please correct me if I have it backwards. I can't get my head around this, need more coffee!

I would conclude the transformer does follow the 4 times rule. 1Meg to

15k in a 7/8" dia and 1-3/16 height package.

Not at all surprising, just never dealt with Henries, let alone 1715 henries. Thanks to those that participated in what some would call folly. Mikek

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It is not a folly, Mike, at least in my opinion. However your refusal to use an ohm meter and try other test methods is kind of a turn-off for me. It is getting difficult to propose a test method. Please continue your posts.

I still will do further tests The only thing won't do at this point is put DC on the windings. I don't consider an ohms test necessary because the manufacturer specifies the DC resistance as 4875 ohms and

330 ohms, 1 meg and 15k respectively. I have confirmation of these numbers from someone that did measure theirs with an ohmmeter.

I'm a little perplexed by the comment, but my IP may have dropped some posts from my threads, but I just went through them all and the only other method I see is below.

From elsewhere, I got,

Several different types of Wien bridges

Use a very low frequency square wave and look at the rise time.

Measure voltage ratio to get turns ratio, then measure 15k winding inductance and calculate 1 meg inductance.

Parallel a known value inductor and measure a smaller value.

What method do you have in mind, if I have the equipment, I would be very happy to set it up and run.

Thanks for the interest, Mikek

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Well, you should get a voltage peak at resonance across a parallel resonant circuit. You should get a voltage null across a parallel resonant circuit only at very low and very high frequencies.

Let's analyze what you've already done first. Taking information from your original post and using no cap and then 60pF cap, I agree that the inductance should be about 1960Hy (which would mean that the secondary distributed capacitance is about 13pF). However that does not square with your Q calculation because the reactance is about 12.3M at 1000Hz. If the winding resistance is about 5000 ohms, then the Q should be about

2400. But, that is with no core loss (parallel R) included. If we now add about 45Megs in parallel with the inductance, it kinda fits.

So, it looks like your original post got close enough.

I apologize, I posted the wrong drawing. I measured voltage across the Resistor not the parallel LC. That is why I adjusted frequency for a null at resonance. Here is the proper one drawing.

Thanks, Mikek

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Your drawing shows a Fluke 9 III. Can't find it.

It works for me, try again.

Not to exciting, just shows I measure across the resistor instead of the coil.

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I found the linked drawing. On the drawing it shows a Fluke 9 III. What's wrong with you?

Are we having some communications problems, or what?

The link works. It shows you using a Fluke 7 iii. If you can find and correct all your errors (including the Fluke 7 iii versus 97 iii), I will try to help.