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I'm playing around with developing a homemade linear potentiometer for a project (and for fun), and I'm stuck wondering: what is the advantage of using a hybrid track design (conductive plastic over a wirewound element) vs simply a conductive plastic as the resistive element?

Assuming the plastic is evenly conductive across it's entire length, with the goal being good linearity, does the hybrid design give any sort of added benefit?

here is an example of the hybrid design I am referencing.

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I'm not familiar with the field of potentiometer design but this seems reasonably understandable:

Why use a wirewound potentiometer at all? They typically have higher power ratings and are more mechanically robust. On the other hand, they have a bumpy feel when moved, and the output varies in noticeable steps as the wiper moves from one turn of the winding to the next.

  • The conductive plastic will smooth out the output steps by being effectively a tiny potentiometer connected between each turn of the winding.

  • A track made purely of soft conductive plastic can wear down with use, making worse contact with the wiper (hence increasing the (effective?) wiper resistance) and also changing the overall response of the potentiometer. My understanding is that this is the limit on the lifetime of common potentiometers.

    • If instead the wire carries the majority of the current, worn spots will have little effect on the resistance curve (and if the plastic wears out entirely, you now have merely a wirewound pot rather than a broken pot).

    • The plastic can be optimized for providing a mechanical bearing surface — as opposed to a predictable resistance — as long as it remains sufficiently conductive to provide an adequately low wiper resistance.

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  • \$\begingroup\$ Thanks for the answer! As a follow up, how would the wearing of the conductive plastic resistive element increase the wiper resistance? I thought the wiper resistance was intrinsic to the construction of the wiper itself? \$\endgroup\$
    – Jordan Z.
    Commented Nov 21, 2017 at 1:14
  • \$\begingroup\$ @JordanZ. I suppose it arguably isn't wiper resistance because it isn't constant. But it's the same effect on the circuit as long as the pot is in that position. And wiper resistance in the normal non-worn-out case would also include the resistance of the wiper-track junction which you can't meaningfully measure independently, and which is what's getting worsened here. Edited to clarify a bit. \$\endgroup\$
    – Kevin Reid
    Commented Nov 21, 2017 at 1:55

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