C0G ceramics vs humidity

Does anyone have reliable information on the affect of humidity on C0G capacitors?

Polypropylene caps will drift about 1/2% from 50 to 90% humidity, polycarb are much worse, maybe 3-4%. I have never seen any numbers on ceramics.

Bob

Reply to
Badbob
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I've never heard of any humidity effects on C0Gs. Fully dense ceramics don't absorb water the way plastic does.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Reply to
Phil Hobbs

Hmm I assume the polypro's I buy are sealed, but maybe there is some long time constant for water leakage?

George H.

Reply to
George Herold

There is. As little as hours for dipped, maybe a week+ for boxed.

Bob

Reply to
Badbob

Kind of what I was thinking, but the way ceramics are made it's hard to say how well sealed they are.

Bob

Reply to
Badbob

On a sunny day (Thu, 09 Apr 2015 07:59:03 +0300) it happened snipped-for-privacy@downunder.com wrote in :

Although I have not tried it that way, it seems to me with a Raspberry Pi (35$) and a USB sound modem (5$) on ebay, you should be able to do it all.

Here:

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The Raspi runs Linux, has ax25, soundmodem I do have it installed on a Raspi IIRC, plus a whole lot of other ham software (sat tracking for example 'predict').

Writing your own AX25 kernel (I did) is not for a beginner (at least not in a resonable amount of time if you are diehard and want to try in asm on a micro). In 2013 I did it (HDLC 1200Bd) in a PIC for data transmission from my model airplane. Slightly modified encrypted protocol, FPV, on screen HUD. Some of thar PIC asm code was published here.

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Reply to
Jan Panteltje

Why not try it?

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John Larkin         Highland Technology, Inc 
picosecond timing   laser drivers and controllers 
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Reply to
John Larkin

I'd exepct no significant effect. If there is anything, it would probably be in the low parts-per-million range.

It would be interesting to measure. Any conventional c-meter would have tempcos that would make that sort of long-term measurement meaningless... even if it had enough resolution.

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John Larkin         Highland Technology, Inc 
picosecond timing   laser drivers and controllers 
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Reply to
John Larkin

That's the kind of thinking I was trying to avoid :^)

Reply to
Badbob

That's the irony. I'm building a capacitance meter who's stability depends on 6 capacitors (it has 6 ranges). C0Gs are a natural, except it would be nice to know if changing humidity would cause drift. I seem to remember seeing hermetic ceramics at one time, but not recently.

It would make an interesting experiment.

Reply to
Badbob

No one has mentioned the possible effect on Leakage. May or may not be more important than the C change.

Mark

Reply to
makolber

I'd try measuring a few before and after boiling them in water for an hour or two. Sort of the T/H equivalent of cold spray and a heat gun.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

Put one cap in a constant-humidity environment, put the other in a humidity-controlled environment, hold the temperature constant, and make some comparisons.

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Tim Wescott 
Wescott Design Services 
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Reply to
Tim Wescott

To avoid multiple effects humidity on drifts --> PCB/SMT components coating, IMHO.

I've done it many years ago on old chassis VME's cards and is also nowadays used by many EMS.

Habib.

Reply to
Habib Bouaziz-Viallet

Not in my application, but maybe in others...

Reply to
Badbob

I don't have that kind of equipment anymore. My test chamber will probably involve a cup half filled with water and a paper towel over it.

Reply to
Badbob

Have you tried asking the manufacturer? I've gotten "inside" information by asking. Typically people who sell stuff want to be helpful. That's what I do.. try and help my customers*.

George H.

*it's not always easy.. other times it's a pleasure.
Reply to
George Herold

I was thinking of an AC Wheatstone bridge with four identical caps, with the output transformer coupled to some AC detector. That could be balanced to PPM resolution. Opposite-arm pairs would be in separate compartments; make it mechanically out of sheet metal or copperclad FR4 maybe, soldered up. Balance it, then put a small wet sponge in one section and a dessicant in another, and see what happens. Reverse wet/dry and compare.

An afternoon project to build, maybe a week or so to take data.

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John Larkin         Highland Technology, Inc 
picosecond timing   laser drivers and controllers 
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Reply to
John Larkin

An FR4 PCB could be expected to have moisture absorption, enough to affect PCB capacitance some.

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John Larkin         Highland Technology, Inc 
picosecond timing   laser drivers and controllers 
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Reply to
John Larkin

I like to get away from a screen+mouse now and then, maybe mill or bend some metal, and solder stuff. Make measurements. Like in the olden days.

The capacitance/humidity measurement would be interesting, given that sub-PPM resolution is likely needed.

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John Larkin         Highland Technology, Inc 
picosecond timing   laser drivers and controllers 
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Reply to
John Larkin

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