Thermistor circuit design

Thread Starter

Zsolt Nagy 1

Joined Jul 4, 2018
3
Greetings everyone!

Can you help me please in the design of a thermistor circuit (with series-parallel resistors preferred), that gives off a linear signal between +10°C and +120°C? I have 5V available.

Thanks for your answers in advance.
 
Last edited:

Thread Starter

Zsolt Nagy 1

Joined Jul 4, 2018
3
Thank you so much, but I'm already through this. I need a solution. I checked this, too: http://mathscinotes.com/2011/07/thermistor-mathematics/

And calculated with Mark Biegert's excel datasheet. But the problem remains: when I choose the mid value between 10°C and 120°C (65-67.5°C), the circuit doesn't work even at room temperature. Somehow the linearization range should be made longer.

Any idea?
 

ericgibbs

Joined Jan 29, 2010
11,923
hi,
OK, could you post a circuit diagram showing the details of the Thermistor and linearising components, so that we can check it out.
E
 

Thread Starter

Zsolt Nagy 1

Joined Jul 4, 2018
3
You can find everything in it, with the values set by me. But the calculations in the spreadsheet aren't my work. The orange fields are filled by the user, they're the ones I filled. The "Desired Ratio @ T1" was 45% from the beginning.

Thanks for the fast reply.
 

Attachments

Last edited:

ericgibbs

Joined Jan 29, 2010
11,923
hi,
I have tried to linearise the thermistor over 10C thru 120C, using a series and parallel resistors.
The linearity is poor even over a much smaller range 20C thru 80C.
What are the accuracy limits in degrees Cdeg are you trying to achieve over 10C to 120C.??
For 10C thru 120C I would choose a semiconductor IC.

E
 

MrAl

Joined Jun 17, 2014
7,971
Hi,

I dont think you can linearize a thermistor that perfectly using linear resistors. You can only get it so good.
You can try pairing a NTC with a PTC but it would probably be too hard to get right.
As Eric suggests, a dedicated IC chip made for measuring temperature would be better in most cases if you need good linearity.
Alternately if you are using a microcontroller, you can linearize in code although some regions will then have higher resolution than others.
 

WBahn

Joined Mar 31, 2012
26,398
Greetings everyone!

Can you help me please in the design of a thermistor circuit (with series-parallel resistors preferred), that gives off a linear signal between +10°C and +120°C? I have 5V available.

Thanks for your answers in advance.
What linearity specs are you trying to meet?

Why are you trying to do this (as opposed to just using a temperature IC)? Is this a course assignment of some kind?
 
Top