[time-nuts] TAPR "PulsePuppy" Pot Selection

[Poul-Henning Kamp]

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In message <CAKn+a3sNg3fE-C8=g-_UTwj3ibmeujGVPfApV5yvR7cNN8FqPw at mail.gmail.com>, Mark Goldberg writes:

>When the pot is used as a voltage divider, theoretically it should have
>the same TC throughout, so temperature effects should not affect the divide
>ratio or the output.

I researched this a bit a couple of years ago in relation to HP5065 C-field tempco

The major tempco in pots are mechanical in nature.

Plastics have *horrid* tempcos, most in the hundreds of
PPM and the best (nylon) barely making it under 20 PPM.

Mind you, that is usually measured on relatively large linear
extrusions, not small bits of geometrically complicated plastic,
like you would use to encapsulate a trimpot.

There are trimpots on the market which claim 5PPM ratio stability,
but the conditions under which that is measured are not very easy
to implement in practice.

If you want anything close to 1PPM trimpots, hunt eBay for "ESI dekapot"


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