Piezo capacitance

Anyone have good guess for the capacitance of a 1" diameter piezo disk?

Likewise, how much capacitance in around 100' of typical telephone twisted pair? ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Jim Thompson
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Probably a few tens of nF for a 20mm 'bender' disk (which will be larger when mounted on the metal backing).

10-20pF per foot comes to mind.

Best regards, Spehro Pefhany

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Spehro Pefhany

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Some call the cable Cat1, but TIA never catagorized anything below Cat3. So 100ohm would be a good guess with out looking up the mfg specs.

Heres the Beldin wire data sheet..

Some vague references to 40 - 50nF / km for 24-26awg TP wire, on the telecom sites.

Cheers

Reply to
Martin Riddle

Gads!

Thanks! ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

1 foot of the RS variety telephone 4-cond cable measured 23pF

Cheers

Reply to
Martin Riddle

Thanks, Martin! ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

I just measured the only piezo disk I have, a .75 inch one. It measures

20 nF.

Cheers, John

Reply to
John - KD5YI

Oops! I found a .9 inch disk. Measures 24 nF.

Reply to
John - KD5YI

I would be willing to bet if you were to use several different model instruments to measure that, you won't get inconsistent readings.. I would think the applied energy from the instrument would cause a piezoelectric (mechanical change) effect there by giving you different readings from one to another..

Just a thought.

Jamie

Reply to
Jamie

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Then you _would_ get inconsistent readings.
Reply to
John Fields

That was an error in my statement, I meant to say "You would get inconsistent readings" Even if all units were calibrated with one source, not the piezo as the calibration source, of course.

Thanks for noticing.

Jamie

Reply to
Jamie

Interesting thought, not sure how inconsistent that number would be though. I worked for an Ultrasonics manufacturer building transducers and amplifiers. After a transducer (PZT8 bonded to aluminum) was complete, I measured the R and C at antiresonance with just a few volts. The tuning components were calculated with the R and C and then the amp drove the assembly at hundreds of volts. I sure hope we didn't mistune because of our low power measurement. That brings up one of my pet quibbles, Ferrites and A sub L. Always specified at one number with no power level attached. Then they are used at several hundred watts, and they are at the input to a radio used a few microwatts. I have never seen a derating of A sub L dependent on power level. Mikek

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amdx

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