Calculating Coefficients for an RTD (Resistance Temperature Detector) Probe

M

MetroBioCen

#1
Hello everybody We sent an RTD to be calibrated. We used this RTD to calibrate our thermometers. Althought the Calibration Certificate is Ok, the coeficients for the RTD are not present. We need those corfficients to be set on the Hart 1502A digital thermometer which uses the RTD, in order to measure temperature. How can I calculate those coefficients. Values of resistance vs temperature are as follows: 84,070Ω -39,965?C 100,1346Ω -0,008?C 139,4873Ω 100,068?C 196,2719Ω 250,119?C 318,3385Ω 599,647?C Thank you very much in advance MetroBioCen
 
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dgriffith

Quite Involved in Discussions
#2
Re: Calculating Coefficients for an RTD Probe

I can't imagine sending a ITS-90 PRT thermometer to a reputable provider and not getting coefficients.
But you're calling it an RTD. Please explain what it is you really sent for cal. Was it a PRT, or an RTD, such as a PT100/IEC-751/DIN-43760?
If RTD, then the coefficiants for those are R0, Alpha, Beta, and Delta:R0=100.1346; Alpha=0.00385; Beta=1.507; Delta=0.111, according to the 1502 manual.
If you have a triple point of water cell (0.01 ?C) you can determine your own R0 and be close enough. If you need it more precise at 0 ?C and can make an ice bath very well, then do that.

Otherwise, if you sent a PRT, then: you got hosed; you didn't ask for the right calibration; you need to look on page two . . . :)
 
Last edited:
M

MetroBioCen

#3
Re: Calculating Coefficients for an RTD Probe

Hi, thank for your answer. The device is in fact a PRT with the following data: Manufacturer: Fluke; Model: 5626. It was calibrated at TESTO Industrial Services GmbH, in Germany. I really ignore why they did not send the coefficients.
 

dgriffith

Quite Involved in Discussions
#4
Re: Calculating Coefficients for an RTD Probe

We have exactly that PRT, which is in fact a secondary standard probe. It is constructed internally just as a SPRT would be, and is very fragile despite the SS sheath. Hart's admonishment is "if you can hear it when you put it down, you've put it down too hard".
Indeed you should have received the derived coefficients (A7,B7,C7, a4,b4) and a 1? conversion table.
Hart is also in England, if it helps.
In any case, that probe needs to go to a specialized thermometry provider, in my opinion.

Call the provider and ask questions.
 
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