How to use a Thermistor 1

[FC72CHF]

Hey can some one give me a quick run down on how to use a thermistor. After some googling, I see that it is common to use the Stienhart-Hart equation. Unfortunately this does not seem to coincide with the info I have. The manufacturer states that the thermistor has a resistivity of 100ohm at 25C and a thermal coefficient of resistance of 2200ppm/C. It is supposed to be linear, but I cant crunch the numbers to match a provided graph.

Someone please fill in the blanks here.

Thermistor paste obtained from:

http://www.electroscience.com/resistor.html

 

[IRstuff]

If you want useful answers, you need to give ALL the information you have, i.e., part number, manufacturer, datasheets, etc. There are dozens of "thermistors" available in the world, we can't possibly guess which one you have.

TTFN

FAQ731-376

 

[FC72CHF]

yikes, man calm down, I dont know any more information and the manufacturer implied that I had every thing I needed in order to use the thermistor

If did have more info, I just might be able to figure it out on my own. Thats why I am asking you guys, because I am lacking quite a bit of info on what the heck is going on.

From what I can see from google, all thermistors follow the same basic laws, thus it is moot that there are dozens of thermistors.

Anyway here is a pdf, pick one...anyone, they just state the resistivity and TCR. I dont know what to do with this.

http://www.electroscience.com/pdf/PTC-2600.pdf

 

[kf2hi]

You linked in your second post to a page about positive tempco (PTC) thermistors. I'm not sure if you can even use the Steinhart-Hart equation for PTC. I know you can apply it to NTC thermistors. But you are better off not using the Steinhart-Hart anyway, unless you have to. On the other hand, the B-parameter equation is much, much easier to use for calculations. It is related to the Steinhart-Hart equation. Read wikipedia on thermistors to understand more about it. As I recall, NTC thermistor datasheets don't always spec B, but if they give R at two temperatures, you can calculate it.
But as I said, I'm not sure those equations even apply to PTC thermistors. Perhaps a simple linear equation works. You should look into it. Do you need PTC or NTC for your application?

 

[kf2hi]

Also, the graphs in the link do make sense. Look at the graph for the PTC 2650. The accompanying text states 5 ohm at 25 C, and tempco 4000 ppm / C. PPM stands for parts per million. That's 0.4 % per C. Now follow the graph from 25 C to 125 C. That's a change of 100 C. 100 X 0.4% is 40 %. The resistance changes from 5 to 7 ohms, or 40 %. The graph agrees with the text.
And by the way, that's not, strictly speaking, a linear relationship between T and R.

 

[ScottyUK]

There's a fair amount of data in the spec sheet, enough to predict how the reistance would change. There's a graph on one of the later sheets showing typical behaviour. What bit are you struggling with?




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If we learn from our mistakes I'm getting a great education!

 

[itsmoked]

Yes you do not use the S-H here just treat this like any other mostly linear transducer someone would use.

Since what you are showing is a make-it-yourself thermistor you will need to make it then characterize it yourself.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[FC72CHF]

aahhhh ok thanks kf2hi, that shows exactly where I was making a mistake

hey thanks guys, always helpful

 

[IRstuff]

That missing datasheet had all the information to have answered your question yesterday, had it been included in the original posting.

TTFN

FAQ731-376

 

[FC72CHF]

Sorry.