# Multifunction DAQ

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## How to calculate Temp from Resister from PT100 equation,

Hi.. everybody,,

This is sound like the Mathematic problem. I measure the voltage (SCXI-1121) of PT100. After I got the signal I need to calculate back to Temp.

My problem is about how to recalculate from the polynomial equation of PT100 as following

Rt=R0[1+at+bt^2+c(t-100)t^3] :

Rt : from measurement
R0 : 100 ohm

I also try with Mathlab (roots() command) and iteration but the answer has a lot of root and complex root in which it is far away from the actual temp value.

I don't know that I did is the wrong solution to get the Temp value ?

Thank you in advance for anybody help.
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## Re: How to calculate Temp from Resister from PT100 equation,

The thermistor constants a, b, and c are supplied by the thermistor manufacturer. So, you should be able to look at the manual or literature for the thermistor to get those constants and calculate the Rt and the temperature. I've linked to a document below that goes through an example calculation.

How Do I Calculate a Thermocouple Reading, That Uses Cold Junction Compensation, By "Hand?"
http://digital.ni.com/public.nsf/websearch/DBF08A40F88F9C8D8525643A00578E53?OpenDocument

Also, if you have LabVIEW, there is a VI that does this conversion from voltage to temperature for you. The VI is called 'Convert Thermistor Reading VI' and can be found in the Data Acquisition>>Signal Conditioning subpalette.

I hope this helps.

Regards,

Todd D.
NI Applications
Engineer
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