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# low temperature coefficient variable resistor

#### jiuning

Mar 27, 2011
3
Hello,

Anyone knows any low temperature coefficient variable resistor? For example, the temperature coefficient is less than 10 ppm/K. I really appreciate if digikey link can be provided. Many thanks.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Digikey lists 320 through-hole resistors with temperature coefficients ranging from 0.2 ppm/K to < 10 ppm/K

It also lists 9864 surface mount resistors with the same specs.

If you're looking for in-stock items, this falls to 57 and 310 respectively.

Use the parametric search Luke! Just search for "precision resistor" and start from there!

#### jiuning

Mar 27, 2011
3
I am looking for variable resistor with low temperature coefficient, rather than two terminal resistor. I found a few 5 ppm/K variable resistors, but there is no variable resistor of less than 5 ppm/K. Thanks anyway.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Ah, sorry. I presumed your use of variable in that was somehow used by you in connection with the thermal coefficient, not that you needed an actual variable resistor.

It strikes me that thermal effects are likely to move the wiper enough to exceed several ppm. And the construction of the path over which it travels is gong to make temperature stability far more of a challenge.

Out of interest, why do you need such high temperature stability?

#### jiuning

Mar 27, 2011
3
Thanks for the explanations.

Actually 100 ppm/K is good enough for me, but I just want to know about the best, out of curiosity.

I need the variable resistor to work as a reference which is connected in serial with a sample. If an AC current of frequency w is passed through the sample and the variable resistor, a 3w signal will be generated on the sample due to heating effect. The variable resistor is adjusted to cancel the 1w signal so that the 3w signal on the sample can be detected. If you are familiar with this you will know that it is the so called 3-omega method. In this way, the reference variable resistor must have much smaller temperature coefficient than that of the sample.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Thanks for that. (Previously the only time I had seen omega and 3 in the same sentence, it referred to fish oil!)

I would suggest that if possible, the resistor used to trim out one of these signals should be kept in an environment that is not affected by the changes in temperature applied to the sample. (But I'm sure you know this)

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