Thermocouples: temperature to emf (or vice verca)
Posted June 1st, 2012 by ChrLie
#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
That's terrific! A lot of
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:
John Weeks
WaveMetrics, Inc.
support@wavemetrics.com
There's a GUI for
There's a GUI for thermocouple emf calculations here: http://umn.edu/~withers/IgorIndex.htm
It does D, K, S, B and R types, and I made some attempt at cold junction compensation. It should convert between emf and temperature in either direction, depending on which setvariable you adjust. John's comment about floating point errors apply to my code too.
Tony.
Himmelkreuzdonnerwetter!
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?
Hi Tony, (I haven't been
Hi Tony,
(I haven't been looking here for a while)
yes, indeed! It is all your fault! ;-)
C
Heyy. Anyone know how to
Heyy. Anyone know how to apply the cold junction compensation for the thermocouple. Thanks