Non-linear pot, more precise in middle

[davidd31415]

Hi,

I took apart a potentiometer that I thought was a simple rheostat. The max resistance between an outer leg and the middle leg was higher than the constant resistance between the two outer legs.

It turns out to have two resistive strips inside and a wiper that connects the two. Each end of the outer strip is connected to an outer leg and the inner leg is connected to one end of the inner strip. As the pot is turned the position where the two strips are jumped together changes.

The strips are of different resistances per length and the pot is non-linear. I notice it appears to have less precision as the wiper approaches the ends.

If there might be another reason why this pot would be designed this way, please let me know what you think. My question is: what would I call a pot like this if I were looking to order one? I've seen precision, and logarithmic, but non-linear alone wouldn't exactly describe this behavior (higher precision in one area)...

Thanks,

Dave

 

[MacGyverS2000]

The very nature of a non-linear resistor denotes a change in precision at different points along the scale. To expect elsewise would require a change in adjustment screw sensitivity over the range in question, and I wouldn't even want to imagine such a mechanical beast.

Or maybe I'm missing something...


Dan - Owner

http://www.Hi-TecDesigns.com

 

[MikeHalloran]

Does it happen to be a throttle position sensor?

That's one place where a nonlinear pot with a sensitive middle would make sense.





Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

They call them "center weighted" and other such things. Often they are customized devices. They use them for stuff like joysticks where maybe you want very accurate control near the center and large motions at the two limits. If you need to buy one as a replacement, you really need to get one from the maker, or you will have quite tussle getting it correct.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[ScottyUK]

One possibility would be a 'balance' pot from an audio application.

Have a look at the ALPS website. They make an enormous variety of pots.

http://www3.alps.co.jp/alpscom/pdf/index_potentiometers-e.html

----------------------------------

Sometimes I only open my mouth to swap feet...

 

[davidd31415]

Thank you all, your responses have been helpful!

One question I still have on this subject:

Is there a term for the "total resistance" of these types of pots? When I say "total" I am refering to the fixed end-to-end resistance, not the minimum or maximum variable resistance.

Thanks,

Dave

 

[itsmoked]

That would be what the pot was called.

"This is a 100K pot"; means the end to end resistance.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[zappedagain]

FWIW - I ran into something similar earlier in the year from Bourns. I turns out they can make a less expensive precision pot with 'trick' materials at the ends of the turns. The only gotcha is that if you want a pot to turn montonically to zero resistance or to max resistance these won't do it. They get jumpy near the ends; if your application stays in the center then they are fine. I was replacing a voltage adjustment pot on a power supply so these wouldn't do.