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

Oh, I see I missed 7 in my drawing where I referred to the Fluke 79 III.

What's wrong with me?

In this same time frame I posted a photo of a Fluke 79 III, I thought you were getting that photo from my link, and also, I thought you missed the 7 in your post when I thought you were referring my photo of the Fluke 79 III. Tough sentence please read slowly, referring to my writing, not your reading ability.

This is what I thought you were seeing.

formatting link

Probably not, I just jumped to an improper conclusion. Mikek

Mikek

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Reply to
amdx
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I made a mistake in my earlier post.

Using 1000Hz, 464Hz, and 60pF, I calculate the stray capacitance to be about 16.5pF. This means that the inductance would have to be about

1540Hy under those conditions.

Please describe how you managed to calculate the Q in detail and there may be more info available.

Reply to
John S

Find the upper and lower 3db points, subtract lower from upper and divide center frequency by the result. Mikek

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Reply to
amdx

Perhaps I asked the wrong question. How did you determine that what you measured was the 3dB points? Voltage ratio? What was the min voltage and what was the 3dB voltage? What was the supply voltage?

Reply to
John S

As you may recall, I have resistor in series with a parallel LC. I am measuring across the resistor, so I look for a null in the voltage. I found resonance by finding the null, then adjusted the the freqgen amplitude so my meter read 0.1V. I then checked to make sure I still was still at null. I recorded the 0.1V. Then I raised the freq until my meter read 1.414V, recorded voltage. I then lower the freq though the null until my voltage again read 1.414V. Then subtract lower from upper and divide center frequency by the result. Sorry, I didn't record the supply Voltage.

Thanks, Mikek

PS. Just for more fun, I rang the coil as follows.

10Hz 113400pf 2230 Henries 15Hz 49630pf 2265 20Hz 28620pf 2210 40Hz 7448pf 2120 60Hz 3362pf 2090 80Hz 1999pf 1977 100Hz 1287pf 1968 140Hz 680pf 1900 Henries 180Hz 414pf 1887 220Hz 280pf 1869 260pf 199.5pf 1878 300Hz 153pf 1839 350Hz 108pf 1914 400Hz 88.3pf 1793 450Hz 62.3pf 2007 500Hz 47.4pf 2137 Henries

These numbers didn't follow a smooth line, which I can't account for, but they're in the ballpark.

I've pretty much ran the course with this and figure the inductance of the 1 Meg winding has an inductance between 1700 Henries and 2000 Henries. I ran these tests with 2.28 times the current of the 3db test you ask about above.

Reply to
amdx

So, are we done or shall we continue with this?

Reply to
John S

I'm happy, it seems to meet the 4 times rule, I found what seems to be an impossibly large inductance in a tiny size. I may make another attempt at finding the SRF, because I'm curious to know if the distributed capacitance is truly in the 11 pf to 20 pf range, (difficult to believe). It looks like the cover may come off of the coil, I'd like to see how it is wound, but I hesitate to remove it. This transformer is getting to be a rare find, I paid $25 for it and don't want to damage it. Thanks for your time and interest, Mikek

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