Generator Polynom Thermocouples


Thread Starter

Rolf Gerste

Hi List

I am looking for a generator polynom to linearise Thermocouple K, J type.

Thanks in advance

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Hoffeldt, Herman (JH)

Hi Rolf

The IPTS-68 standard defines thermocouple voltages as a function of temperature according to the following polynomial equation:
V = C0 + C1*T + C2*T*T + C3*T*T*T+...Cn*(T)^n
V - Thermocouple voltage in units of microV (10^(-6)V)
T - Temperature in Degrees Celsius
C1,C2,C3..Cn - Polynomial Coefficients

For Type J:
Range -210 to 760deg.C, order = 7
C0 = 0
C1 = 5.0372753027E+1
C2 = 3.0425491284E-2
C3 = -8.5669750464E-5
C4 = 1.3348825735E-7
C5 = -1.7022405966E-10
C6 = 1.9416091001E-13
C7 = -9.6391844859E-17

Range 760 to 1200degC, order = 5
C0 = 2.9721751778E+5
C1 = -1.5059632873E+3
C2 = 3.2051064215E+0
C3 = -3.221017423E-3
C4 = 1.5949968788E-3
C5 = -3.1239801752E-10

For Type K:
Range -270 to 0 Deg.C, order = 10
C0 = 0
C1 = 3.9475433139E+1
C2 = 2.7465251138E-2
C3 = -1.6565406716E-4
C4 = -1.5190912392E-6
C5 = -2.4581670924E-8
C6 = -2.4757917816E-10
C7 = -1.5585276173E-12
C8 = -5.9729921255E-15
C9 = -1.2688801216E-17

Range 0 to 1372 Deg.C, order = 8
C0 = -1.8533063273E+1
C1 = 3.8918344612E+1
C2 = 1.6655154356E-2
C3 = -7.8702374448E-5
C4 = 2.2835785557E-7
C5 = -3.5700231258E-10
C6 = 2.9932909136E-13
C7 = -1.2849848798E-16
C8 = 2.2239974336E-20

That's it
Another alternative to using a polynomial for thermocouple linearization, is to use a piecewise linear approximation. this may involve quite a bit less calculating, depending on the accuracy you need and the range over which you want to operate. To do that, you need the thermocouple tables so you can define the breakpoints. I have them in electronic form if you 'd like to try

Rick Daniel
Intelligent Instrumentation
This is the coefficients to convert T° in Volt, but I would like to have the coefficients to convert volt in T° (for T° RAnge -100°C to 200°C). Do you have them? or where can I find them?

Bruce Durdle

74th edition of the CRC Handbook pages15-10 on has the coefficient tables for calculation of temperature from emf values. They reference NIST monograph 175.