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Old 03-14-2012, 03:00 PM #1
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Default Calculating Temperature Based on Thermistor Resistance?

I'm trying to gain a working understanding of how to determine temperature based on thermistor resistance. My purpose is to be able to read the internal temperature of a Coherent Sapphire, based on thermistor leads that I have access to through the pinout.

Here's what's catching me:

- All I know about the thermistor itself, is that it is a "standard type 10K at 25C"

From what I've read, any time you want to calculate the actual temperature using a thermistor, you need some combination of additional coefficients, or a "beta" and "alpha" value. From what I've found in searching part numbers, even across multiple "10K at 25C" thermistors, there seem to be different (or a lack of) figures stated for beta/alpha.

Regardless, I know that somehow the resistance, coupled with the knowledge that this is a "standard type 10K at 25C" thermistor, has been enough information to allow temperature reading in this scenario.


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Old 03-14-2012, 05:21 PM #2
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Default Re: Calculating Temperature Based on Thermistor Resistance?

Quote:
Originally Posted by rhd View Post
I'm trying to gain a working understanding of how to determine temperature based on thermistor resistance. My purpose is to be able to read the internal temperature of a Coherent Sapphire, based on thermistor leads that I have access to through the pinout.

Here's what's catching me:

- All I know about the thermistor itself, is that it is a "standard type 10K at 25C"

From what I've read, any time you want to calculate the actual temperature using a thermistor, you need some combination of additional coefficients, or a "beta" and "alpha" value. From what I've found in searching part numbers, even across multiple "10K at 25C" thermistors, there seem to be different (or a lack of) figures stated for beta/alpha.

Regardless, I know that somehow the resistance, coupled with the knowledge that this is a "standard type 10K at 25C" thermistor, has been enough information to allow temperature reading in this scenario.
Come on RHD...... (took 5 seconds)

http://www.thermo-dynamics.com/pdfil...p_vs_resis.pdf

and there are a lot more...


Jerry
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Last edited by lasersbee; 03-14-2012 at 05:23 PM. Reason: Spelling errors
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Old 03-14-2012, 05:31 PM #3
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Default Re: Calculating Temperature Based on Thermistor Resistance?

Quote:
Originally Posted by lasersbee View Post
Come on RHD...... (took 5 seconds)

http://www.thermo-dynamics.com/pdfil...p_vs_resis.pdf

and there are a lot more...


Jerry
Thanks for the link, but I've found lots of those charts. They're not difficult to locate. The problem, is that for 10K @ 25C thermistors, I've seen a number of those charts. Yours indicates 0 degrees at 32,630.

This one:
Technical Reference - Thermistor Resistance Table
indicates 0 degrees at 29,490.

Clearly the tables vary based on the part, and apparently knowing that you have 10K @ 25C is not enough to pin down exactly what your resistance-to-temperature correlation will be.
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- The Necessity of Safety Goggles (link)

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Old 03-14-2012, 05:47 PM #4
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Default Re: Calculating Temperature Based on Thermistor Resistance?

That depends on the manufacturer and the exact part number...
There are variations and different spec tolerances between
manufacturers of the same 10K part. Just look at the chart
you linked to. There are two 10K thermistors on it...

You would need to know the part number of the specific part
that you have...

It also depend on how accurate you need your readings...

I have 2 thermistors on my Coherent FAP Laser and decided to
add 2 digital 1-wire sensors instead of trying to figure out the
exact curve of the 2 thermistors on the head and heatsink...
The 1-Wire sensor are accurate enough for my use...

Jerry
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Last edited by lasersbee; 03-14-2012 at 05:51 PM. Reason: Spelling errors
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