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I have to measure the temperature of a liquid. Does a PTC thermistor has any advantage over an NTC one? I mean, are there conditions where one is preferred over the other?

SamGibson
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Manzillo
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  • you know thermistors are very non linear? implement a lookuptable with some supporting points, and interpolate linear in between... done that some years ago, worked like a charm. So you get an almost precise value – schnedan Sep 18 '20 at 16:49
  • @schnedan yep I know, thanks! My only doubt is whether one of the two might be a better solution with respect to the other – Manzillo Sep 18 '20 at 16:58
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    NTC today are not so bad, but limited in max temperature. when it comes to temperature span and precision platinum based PTC's are the reference. ceramic PTC are very non linear and just good to detect too hot / too warm. Silicon based KTYxx-Series PTC's are cheep and good enough for many applications – schnedan Sep 18 '20 at 17:09
  • In a nutshell: lookup and interpolation will make either (and almost any) work. Whichever has the best matching dynamic range (to your analog front-end), over the intended temperature range, will make the best sensor in this application. – rdtsc Sep 18 '20 at 17:24

2 Answers2

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Most thermistors used for measuring temperature are NTC. They are specified relatively tightly in terms of their parameters for that application.

They usually change quite a bit with temperature, of the order of -5% for every degree C, so that they end up being very nonlinear, to the point that for a wide temperature range you need a lot of dynamic range in the measuring circuitry or you lose resolution at the extremes. For example a thermistor may be 10K nominal at 25°C but only 516 ohms at 125°C, and 210K at -40°C.

There are some PTC thermistors designed for measuring temperature, they tend to have more gentle temperature coefficients (such as the silicon resistance types).

There are also RTDs which are (sometimes pure noble) metals which tend to change about +0.4%/°C near room temperature.

Spehro Pefhany
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PTC thermistors are used when you want to increase the resistance offered with an increase in temperature. NTC is used when you want to reduce the resistance for an increase in temperature.

PTC thermistors are used as resettable fuses in circuits. When the current flow increases, the temperature increases, and the PTC thermistor resistance increases, and the current flow is reduced.

But using NTC or PTC thermistor depends on the circuit you want to design.

Srinivasan M P
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