Thermocouples: temperature to emf (or vice verca)

#pragma rtGlobals=1 // Use modern global access method. //The function emf2T converts a thermocouple electromotive force (emf, in milli volts to temperature (in Celsius) or vice verca; //currently for B, S and C-Type thermocouples. All coefficients taken from ASTM E-230. // //syntax: emf2T(TC_string, temp, emf) //Parameters: TC_string is a string indicating the thermocouple type, here B, S or C // tmp is temperature in Celsius // emf is the emf in mV // The value that needs to be calculated must be entered as NaN // //To convert a temperature into an emf value use e.g. print emf2T("B", 1400, nan) //To convert emf to temperature use e.g. print emf2T("B", nan, 8.956) function emf2T(type, Tmp, emf) string type variable Tmp, emf variable c0, c1,c2,c3,c4,c5,c6,c7,c8, c9 c1 = 0 //if not assigned later make sure they are all zero c2 = 0 c3 = 0 c4 = 0 c5 = 0 c6 = 0 c7 = 0 c8 = 0 c9 = 0 // ********************************************************************************************* // *********************** B- Type thermocouples Pt6%Rh / Pt30%Rh ************************* // ********************************************************************************************* strswitch(type) case "B": if (numtype(Tmp) == 0 && numtype(emf) == 2) // this is a temperature to EMF conversion if (tmp >= 0 && tmp <= 630.615) c0 = 0.000000000000E+00 c1 =-0.246508183460E-03 c2 = 0.590404211710E-05 c3 =-0.132579316360E-08 c4 = 0.156682919010E-11 c5 =-0.169445292400E-14 c6 = 0.629903470940E-18 c7 = 0 c8 = 0 return c0*tmp^0 + c1*tmp^1 +c2*tmp^2 +c3*tmp^3 +c4*tmp^4 +c5*tmp^5 +c6*tmp^6 +c7*tmp^7 +c8*tmp^8 endif if (tmp > 630.615 && tmp <= 1820) c0 = -0.389381686210E+01 c1 = 0.285717474700E-01 c2 =-0.848851047850E-04 c3 = 0.157852801640E-06 c4 =-0.168353448640E-09 c5 = 0.111097940130E-12 c6 =-0.445154310330E-16 c7 = 0.989756408210E-20 c8 =-0.937913302890E-24 return c0*tmp^0 + c1*tmp^1 +c2*tmp^2 +c3*tmp^3 +c4*tmp^4 +c5*tmp^5 +c6*tmp^6 +c7*tmp^7 +c8*tmp^8 endif endif if (numtype(Tmp) == 2 && numtype(emf) == 0) // this is a EMF to temperature conversion if (emf >= 0.291 && emf <= 2.431) c0 = 9.8423321E+01 c1 = 6.9971500E+02 c2 = -8.4765304E+02 c3 = 1.0052644E+03 c4 = -8.3345952E+02 c5 = 4.5508542E+02 c6 = -1.5523037E+02 c7 = 2.9886750E+01 c8 = -2.4742860E+00 return c0 + c1*emf^1 +c2*emf^2 +c3*emf^3 +c4*emf^4 +c5*emf^5 +c6*emf^6 +c7*emf^7 +c8*emf^8 endif if (emf > 2.431 && emf <= 13.82) c0 = 2.1315071E+02 c1 = 2.8510504E+02 c2 = -5.2742887E+01 c3 = 9.9160804E+00 c4 = -1.2965303E+00 c5 = 1.1195870E-01 c6 = -6.0625199E-03 c7 = 1.8661696E-04 c8 = -2.4878585E-06 return c0 + c1*emf^1 +c2*emf^2 +c3*emf^3 +c4*emf^4 +c5*emf^5 +c6*emf^6 +c7*emf^7 +c8*emf^8 endif endif break // ********************************************************************************************* // *********************** S- Type thermocouples Pt / Pt10%Rh ****************************** // ********************************************************************************************* case "S": if (numtype(Tmp) == 0 && numtype(emf) == 2) // this is a temperature to EMF conversion if (tmp >= -50 && tmp <= 1064.18) c0 = 0.000000000000E+00 c1 =0.540313308631E-02 c2 = 0.125934289740E-04 c3 =-0.232477968689E-07 c4 = 0.322028823036E-10 c5 =-0.331465196389E-13 c6 = 0.255744251786E-16 c7 =-0.125068871393E-19 c8 = 0.271443176145E-23 return c0*tmp^0 + c1*tmp^1 +c2*tmp^2 +c3*tmp^3 +c4*tmp^4 +c5*tmp^5 +c6*tmp^6 +c7*tmp^7 +c8*tmp^8 endif if (tmp > 1064.18 && tmp <= 1664.5) c0 = 0.132900444085E+01 c1 = 0.334509311344E-02 c2 = 0.654805192818E-05 c3 = -0.164856259209E-08 c4 = 0.129989605174E-13 return c0*tmp^0 + c1*tmp^1 +c2*tmp^2 +c3*tmp^3 +c4*tmp^4 +c5*tmp^5 +c6*tmp^6 +c7*tmp^7 +c8*tmp^8 endif if (tmp > 1664.5 && tmp <= 1768.1) c0 = 0.146628232636E+03 c1 = -0.258430516752E+00 c2 = 0.163693574641E-03 c3 = -0.330439046987E-07 c4 = -0.943223690612E-14 return c0*tmp^0 + c1*tmp^1 +c2*tmp^2 +c3*tmp^3 +c4*tmp^4 +c5*tmp^5 +c6*tmp^6 +c7*tmp^7 +c8*tmp^8 endif endif if (numtype(Tmp) == 2 && numtype(emf) == 0) // this is a EMF to temperature conversion if (emf >= -0.235 && emf <= 1.874) c0 = 0 c1 = 1.84949460E+02 c2 = -8.00504062E+01 c3 = 1.02237430E+02 c4 = -1.52248592E+02 c5 = 1.88821343E+02 c6 = -1.59085941E+02 c7 = 8.23027880E+01 c8 = -2.34181944E+01 c9 = 2.79786260E+00 return c0 + c1*emf^1 +c2*emf^2 +c3*emf^3 +c4*emf^4 +c5*emf^5 +c6*emf^6 +c7*emf^7 +c8*emf^8 +c9*emf^9 endif if (emf > 1.874 && emf <=11.950) c0 = 1.291507177E+01 c1 = 1.466298863E+02 c2 = -1.534713402E+01 c3 = 3.145945973 c4 = -4.163257839E-01 c5 = 3.187963771E-02 c6 = -1.291637500E-03 c7 = 2.183475087E-05 c8 = -1.447379511E-07 c9 = 8.211272125E-09 return c0 + c1*emf^1 +c2*emf^2 +c3*emf^3 +c4*emf^4 +c5*emf^5 +c6*emf^6 +c7*emf^7 +c8*emf^8 +c9*emf^9 endif if (emf > 11.950 && emf <= 17.536) c0 = -8.087801117E+01 c1 = 1.621573104E+02 c2 = -8.536869453E+00 c3 = 4.719686976E-01 c4 = -1.441693666E-02 c5 = 2.081618890E-04 return c0 + c1*emf^1 +c2*emf^2 +c3*emf^3 +c4*emf^4 +c5*emf^5 +c6*emf^6 +c7*emf^7 +c8*emf^8 endif if (emf > 17.536 && emf <= 18.693) c0 = 5.333875126E+04 c1 = -1.235892298E+04 c2 = 1.092657613E+03 c3 = -4.265693686E+01 c4 = 6.247205420E-01 return c0 + c1*emf^1 +c2*emf^2 +c3*emf^3 +c4*emf^4 +c5*emf^5 +c6*emf^6 +c7*emf^7 +c8*emf^8 endif endif break // ********************************************************************************************* // *********************** C- Type thermocouples W5%Re / W26%Re ***************************** // ********************************************************************************************* case "C": if (numtype(Tmp) == 0 && numtype(emf) == 2) // this is a temperature to EMF conversion if (tmp >= 0 && tmp <= 630.615) c0 = 0.0000000 c1 = 1.34060323e-2 c2 = 1.19249923e-5 c3 = -7.98063543e-9 c4 = -5.07875153e-12 c5 = 1.31641973e-14 c6 = -7.91973323e-18 return c0*tmp^0 + c1*tmp^1 +c2*tmp^2 +c3*tmp^3 +c4*tmp^4 +c5*tmp^5 +c6*tmp^6 endif if (tmp > 630.615 && tmp <= 2315) c0 = 4.05288233e-1 c1 = 1.15093553e-2 c2 = 1.56964533e-5 c3 = -1.37044123e-8 c4 = 5.22908733e-12 c5 = -9.20827583e-16 c6 = 4.52451123e-20 return c0*tmp^0 + c1*tmp^1 +c2*tmp^2 +c3*tmp^3 +c4*tmp^4 +c5*tmp^5 +c6*tmp^6 endif endif if (numtype(Tmp) == 2 && numtype(emf) == 0) // this is a EMF to temperature conversion c0 = 0.0 c1 = 7.4124732e1 c2 = -4.28082813 c3 = 5.21138920e-1 c4 = -4.57487201e-2 c5 = 2.80578284e-3 c6 = -1.13145137e-4 c7 = 2.85489684e-6 c8 = -4.07643828e-8 c9 = 2.51358071e-10 return c0 + c1*emf^1 +c2*emf^2 +c3*emf^3 +c4*emf^4 +c5*emf^5 +c6*emf^6 +c7*emf^7 +c8*emf^8 +c9*emf^9 endif break default: break endswitch return NaN // if non of the other if-statements are entered, return NaN end

johnweeks

That's terrific! A lot of effort typing in all those constants!

I would comment that the straightforward method of evaluating a polynomial has potential problems caused by floating-point truncation errors. A better way to do it is outlined in Numerical Recipes. This method is followed by the Igor poly() function, so I would recommend poly(). To use it, you need to create a wave with the coefficients, something like this fragment that implements just one part of your function:


			if (tmp > 630.615 && tmp <= 2315)
 
 				Make/D/FREE cw = {4.05288233e-1,  1.15093553e-2,   1.56964533e-5, -1.37044123e-8, 5.22908733e-12, -9.20827583e-16, 4.52451123e-20}
 
				return poly(cw, tmp)
			endif

John Weeks
WaveMetrics, Inc.
support@wavemetrics.com

June 1, 2012 at 08:55 am - Permalink

tony

There's a GUI for thermocouple emf calculations here: https://www.wavemetrics.com/node/21411
It does S, B, R, K, T, E, J, N, C, and D types, and includes cold junction compensation. It should convert between emf and temperature in either direction, depending on which setvariable you adjust.

June 27, 2012 at 09:43 am - Permalink

tony

Himmelkreuzdonnerwetter! I've just noticed the identity of the original poster - Hi Christian! I guess there aren't so many people out there using types C and D :) I wonder, was it I who introduced you to the delights of Igor back in Hannover in the late 90s, or did you pick it up somewhere further on down the line?

June 29, 2012 at 11:17 am - Permalink

ChrLie

Hi Tony,

(I haven't been looking here for a while)
yes, indeed! It is all your fault! ;-)

C

July 5, 2012 at 03:06 am - Permalink

Tanay

Heyy. Anyone know how to apply the cold junction compensation for the thermocouple. Thanks

August 21, 2012 at 02:31 pm - Permalink

tony

After many years, I have released my thermocouple calulator GUI as an IgorExchange project. I'll update the link in this thread, in case anyone out there is interested in such a thing.

September 24, 2020 at 02:26 am - Permalink

Thermocouples: temperature to emf (or vice verca)

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