Talk:Thermistor

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The first section merely states the definition of a first-order approximation, without mentioning the applicability (or lack thereof) to most thermistors. It then goes on to offer the differential form without adding the solution to that equation. A visit to digikey shows that thermistors being sold are rarely identified by k value OR alpha (linear and exponential models are rather poor, the linear model is sometimes used for "normal" resistors).

Since (I'm guessing) the vast majority of people coming to this page are interested in thermistors from the perspective of using/choosing one for a project, I proposed removing this section, and replacing it with a more hacker/tinkerer-friendly explanation of functionality (charge carriers increase/decrease resulting in more or less resistivity, named ntc/ptc for that reason) and an equation that will make use of the β and R_o values typically given:

${\displaystyle {\frac {1}{T}}={\frac {1}{T_{0}}}+{\frac {1}{B}}\ln \left({\frac {R}{R_{0}}}\right)}$ 

And explaining that R₀ and T₀ are the values commonly given in datasheets.

Possibly go on to explain that β effectively changes with temperature (causing manufacturers to spec multiple β values), which leads into the next section. — Preceding unsigned comment added by 209.6.41.153 (talk) 02:09, 27 February 2015 (UTC)Reply

Who is your target audience? A scientist knows this better. An electronic engineer doesn't need it. Neither do enthusiasts who may want to learn about it's use. For them it's far too high. What most people would would need is HOW ARE THEY MARKED AND HOW TO CALCULATE THE RESISTANCE AT A TEMPERATURE. Explain it on a simple and straightforward way.

I agree that this article should include a simple and straightforward explanation "up front".

After that, later sections "down below" should be written for an expert reader who may want to be reminded of some technical detail.

See the Wikipedia:Make technical articles understandable guideline for more details of the 3 target audiences. --DavidCary (talk) 19:26, 3 March 2014 (UTC)Reply

I totally agree: I came here to find the critical parameters to allow me to select a Thermister. I left no wiser.

"If you can't explain it to a six year old, you don't understand it yourself" Albert Einstein Gutta Percha (talk) 23:30, 3 March 2014 (UTC)Reply

Nice article. One question: "Many NTC thermistors are made from a thin coil of semiconducting material such as a sintered metal oxide. They work because raising the temperature of a semiconductor increases the number of electrons able to move about and carry charge - it promotes them into the conducting band". This is nice simple explanation for NTC, but how does PTC work then? Thanks! --User:Chinasaur

Not really, not a nice article. Full of mistakes and there is no acknowledgement of the corrections. Possibly written by a first year physics or science student.

I've seen the b-constant specified on many datasheets for thermistors, yet can't find a good description of it. My understanding is that it is a way to approximate the R-T relationship that is much worse than the Steinhart-Hart equation? --User:Pigrew

Yes, when I simplify the 3rd-order Steinhart-Hart equation by forcing c=0, I get the somewhat less accurate 2nd-order beta equation. The beta equation is still more accurate than the 1st-order approximation. How could we make the Thermistor#B or β parameter equation section better? --DavidCary (talk) 19:26, 3 March 2014 (UTC)Reply

I removed this application:

• Thermistors are used in smart camera flash guns which adjust for proper film exposure according to the light reflected.

Wow - it appears to have been in the article a long time. I think this is totally wrong because thermistors aren't light sensitive! The author must have been thinking photoresistor, but those are typically slower and used to determine exposure when no flash is used. I could also see them used in flash battery packs, but again, no light-sensing application.

I added the B (beta) parameter equations. They are the ones used by engineers. Mircealutic 18:55, 21 December 2005 (UTC)Reply

Thank you, Mircealutic! --DavidCary (talk) 19:26, 3 March 2014 (UTC)Reply

Trivial point but there must be a better picture of a thermistor out there. Also it may be an idea to get it put onto the page rather that linking to it. Wheatleya 22:11, 22 February 2006 (UTC)Reply

That blown inrush current limiter is a PTC, not an NTC. A PTC has higher resistance, when getting hot, so limiting the current. Eur (talk) 22:53, 26 January 2019 (UTC)Reply

I noticed that pic description too. Maybe confusing "inrush limiting PTC" with a "circuit breaking safety device" in which case it's meant to fail in adverse conditions like an AC voltage spike. I have seen both after they failed, they do look similar. Neither is meant to measure temperature. But is the other one NTC then? Original pic poster account no longer exists. Perhaps the pic was introduced here only because it was incorrectly labelled as NTC. Walkingstick3 (talk) 23:23, 2 March 2023 (UTC)Reply

Our physics laboratory tutor claims that all the thermistors are NTC type and in fact there are no such that of the coefficient positive. Or maybe it is just him who hasn't met them yet.

A combination of a ptc and an ntc thermistor have been used to control CRT degauss coils since the year dot.

Tabby (talk) 23:39, 11 January 2008 (UTC)Reply

The first B-parameter equation is incorrect. It is algebraically inconsistent with the second B-parameter equation, which is correct. The first equation should be... 1/T = 1/T0 + ln(R/R0)/B. Please note also that T0 in these formulas is Kelvin temperature, while the last part of the B-parameter addition says "R0 is the resistance at temperature T0 (usually 25C)". It should say "T0 (usually 298.15K)". That's the same temperature, of course, but if 25 is used in the equations as T0, they won't work. -- John O'Flaherty

Hopefully they are fixed, but please check. PAR 17:56, 2 August 2006 (UTC)Reply

It looks right, now. Also added parentheses around the denom. in eqn.4 of that section. J.O'F,8-5-2006.

A very nice article. Thank you!

However I think there is a mistake: Using the parameters you give for a 3 KOhms thermistor

a = 1,40E-03 b = 2,37E-04 c = 9,90E-08

at 25°C (= 298.15 K) I get a resistance of 5264,260842 Ohms. The expected value of 3000 Ohms I get at 35.9906°C. Is there an error in the parameters?

Another question: Can you please publish the parameters for most common thermistors (like 30K, 100K), or help me where I can find them?

Email: m31415@nurfuerspam.de

Thanks,

Martin

I don't know what you did wrong but when I use:

${\displaystyle R=e^{{\left(\beta -{\alpha \over 2}\right)}^{1 \over 3}-{\left(\beta +{\alpha \over 2}\right)}^{1 \over 3}}}$ 

with T=298.15, I get 3067.5 ohms, which is off by about 2 percent, which is about the roundoff error in the abc coefficients. If you still get a different answer, list all your steps and values, so we can find the error. Theres a lot of good information at the at the YSI technical page PAR 15:22, 7 August 2006 (UTC)Reply

• I just ran in to the same problem.... I had mistaken alpha for a in the "beta=" equation because this mistake had been made in the Steinhart-Hart_equation page (now fixed). But this article had an error in the R= equation, too (what PAR found)- it used a instead of alpha. So I changed the units to x and y instead of alpha and beta to avoid confusion. It should work now - I verified it with the example & got 3067.500051 —Preceding unsigned comment added by Morcheeba (talk • contribs) 18:39, 3 February 2010 (UTC)Reply

Equation of R in function of T is wrong!

NO MERGE - these are two entirely different devices and should not be confused. PAR 16:08, 1 February 2007 (UTC) Seconded. Different principles are at work here (& different equations to approximate) Morcheeba (talk) 18:41, 3 February 2010 (UTC)Reply

Dear Author of the article “Thermistor” I would like to draw attention to some misuses of language that plague technical literature. You start your article with the definition of a thermistor:

“A thermistor is a type of resistor with resistance inversly proportional to its temperature.” A physical quantity y is said to be inversely proportional to a quantity x if the following equation holds:y=A/x where A is a quantity that does not depend on x. What you wanted to say is that the function R(T) is monotonically decreasing. Note that monotonic decrease and inverse proportionality have absolutely no relationship with each other. For instance the function y(x)=A/x is increasing rather than decreasing if x>0 and A <0 and even if A >0 one has y(x₁)<y(x₂) for all x₁<0 and 0<x₂ even though for these values one has x₁ < x₂ .

Another comment I would like to make: It would be nice to write equations in technical literature always in unit independent form so that it is unnecessary to state in which units the quantities have to be used. For instance the equation

1/T = a + b ln(R) + c ln3(R)

Should be written as

1/T = a + b ln(R/ohm) + c ln3(R/ohm)

and the values of the constants are

a=1.4 10-3/K
b=2.37 10-4/K
c=9.90 10-8/K
This way the user of the formula may write his values with any kind of units 

and the result will not depend on the units he uses. Sincerely Yours Bernhard Lesche —Preceding unsigned comment added by 200.17.69.109 (talk) 13:20, 8 January 2009 (UTC)Reply

"Over small changes in temperature, if the right semiconductor is used, the resistance of the material is linearly proportional to the temperature." This cannot be true for an NTC thermistor unless the resistance is negative. I think that what is meant is, "Over small changes in temperature, if the right semiconductor is used, the rate of change of resistance of the material with respect to the temperature is constant." However, I suggest that this observation is trivial, since it is true for any differentiable function. —Preceding unsigned comment added by 63.86.92.198 (talk) 13:22, 5 August 2009 (UTC)Reply

Using a numerical exempel it's easy to verify that the correct formula for ß in the rearranged Steinhart-Hart equation is:

beta = sqrt ((b / 3c)³ + alpha² / 4)

not:

beta = sqrt ((b / 3c)³ + a² / 4)

For example using a thermistor with these properties (typical values of part number B57861S0103F040):

T = 243.15 K -> R = 177000 ohm
T = 273.15 K -> R = 32650 ohm
T = 303.15 K -> R = 8057 ohm

and solving the system of linear equations from entering these into the Steinhart-Hart equation gives:

a = 0.0011249909
b = 0.00023475694
c = 0.000000085529225

Using T = 273.15 K gives:

alpha = -29650.698

Note how (b / 3c)³ = 765857450, (a² / 4) = 0.00000031640113 and (alpha² / 4) = 219790970

Adding (b / 3c)³ and (a² / 4) obviously make little sense, considering the big difference in magnitude.

Using the corrected formula with (alpha² / 4) above:

beta = 31395.038

R = e ^ ((beta - alpha / 2) ^ (1 / 3) - (beta + alpha / 2) ^ (1 / 3)) = 32650.027

which is the expected result (after some rounding errors)

Instead using (a² / 4) would give R = 96345.655

Shirifan (talk) 20:35, 13 January 2010 (UTC)Reply

Some Thermistors are given a "Climatic Category" in accordance with IEC 60068-1. This is a way of representing the temperature specifications of a thermistor using three different numbers separated by a slash (/). For example, a Climatic Category 55/155/56. The first number is the minimum operating temperature expressed in negative degrees Celsius. The second is maximum operating temperature in positive degrees Celsius. The last is the duration of test Ca (damp heat, steady state) at a relative humidity of 93% +2/-3% and an ambient temperature of 40 °C. —Preceding unsigned comment added by Girmann (talk • contribs) 21:00, 13 August 2010 (UTC)Reply

The Jim Williams ap note discusses Wien bridge oscilators and thermisters, but not both together, at least on the pages listed.Constant314 (talk) 05:17, 30 January 2012 (UTC)Reply

What is needed for this paragraph is a reference that says that there is a "thermistor principal" and its exact definition. Its use in this paragraph suggests that any two terminal device exhibiting an increase of resistance as it get hotter is exhibiting "thermistor principal". NTC (Negative temperature coefficient) thermistors are far more prevalent than PTC thermistors, so if there is a thermistor principal it would mean a device showing a decrease of resistance as it got hotter. Furthermore the second paragraph of this very article says "Thermistors differ from resistance temperature detectors (RTD) in that the material used in a thermistor is generally a ceramic or polymer, while RTDs use pure metals." A lamp is much more like an RTD than a thermistor.Constant314 (talk) 03:43, 2 February 2012 (UTC)Reply

The history section says that "The first NTC thermistor was discovered in 1833 by Michael Faraday", but that "The thermistor was invented by Samuel Ruben in 1930". Surely these two statements cannot both be correct. At the very least some clarification seems to be required. 86.167.6.253 (talk) 16:36, 25 October 2012 (UTC)Reply

Appears to be solved, by saying "A commercially viable thermistor was invented..." Walkingstick3 (talk) 23:44, 2 March 2023 (UTC)Reply

According to the article Iron–hydrogen resistor some early thermistors were made from uranium dioxide. This might be worth including in the history section.150.227.15.253 (talk) 15:00, 22 September 2022 (UTC)Reply

The article started out so good and then it becomes useless at the temperature coefficient of resistance formula. Please explain everything and don't use the lazy approach, use the redundant one. For example: What does the d mean? Is it a substitute for a Delta or does it mean something else? Is the R(T) another equation? Which equation is inserted?
--Jangirke (talk) 20:05, 21 March 2013 (UTC)Reply

"R(T)" is standard notation for a function. It simply means the resistance at a particular temperature. An approximation of R(T) may be expressed by an equation. "dR/dT" is standard notation for the first derivative of Resistance with respect to Temperature. It refers of the slope of resistance vs temperature curve at a particular temperature. Constant314 (talk) 02:34, 22 March 2013 (UTC)Reply

Is the electrical symbol correct? The same symbol is for the varistor and the two are not the same. Here by us we use another symbol for thermistor that has the little horizontal line vertical. TrinarSK (talk) 10:16, 9 April 2013 (UTC)Reply

I've also seen a resistor with a circle around it as a schematic symbol for a thermistor. I think this should be mentioned or highlighted on the page as well. Kchoboter (talk) 02:05, 6 December 2013 (UTC)Reply

This statement is incorrect. "PTC thermistors 'latch' into a hot / low resistance state: once hot, they stay that way, until cooled", when the device is hot the resistance is high, causing a larger voltage drop across the device that dissipates heat and keeps the device latched. It should read, "PTC thermistors that have become hot, and therefore have higher resistance, will remain hot; the higher resistance causes more voltage drop across the device ensuring the resistance does not drop. This hysteresis can be used as a latch." Nagaru (talk) 19:22, 14 October 2015 (UTC)Reply

The two IEC standard symbols are missing, and none of the images found in Commons are correct. Widefox; talk 23:29, 29 January 2018 (UTC)Reply

I think the article lacks a clear explanation of the difference between a thermistor and a resistance thermometer, as does the Wikipedia article called "Resistance thermometer" https://en.wikipedia.org/wiki/Resistance_thermometer. I found it very frustrating to read the two articles and find that neither of them explains this. Polar Apposite (talk) 17:15, 19 January 2023 (UTC)Reply