This is in a sense the reciprocal or converse function of the equation for converting voltage to temperature:
For all types of thermocouples (except K at t>0°C), we have:
$$ V(mV) = \mathop \sum \limits_{i = 0}^n {\left( {{t_{90}}} \right)^i} $$
For type K thermocouples at temperatures above 0°C, we have:
$$ T\left( {^\circ C} \right) = {T_{inf}}\left( {^\circ C} \right) + \frac{{V – {V_{inf}}}}{{{V_{sup}} – {V_{inf}}}} $$
Ci = Coefficients from C0 to Cn
t90 = Temperature of the thermocouple in °C
a0 to a2 = Specific coefficients of exponentiation only for type K thermocouples and temperatures above 0 °C
e= natural logarithm constant: 2.71828…
Example of coefficients for type K thermocouples | ||
Temperature (°C) | -270 to 0 | 0 to 1372 |
c0 | 0 | -0.176004136860e-1 |
c1 | 0.394501280250e-1 | 0.389212049750e-1 |
c2 | 0.236223735980e-4 | 0.185587700320e-4 |
c3 | -0.328589067840e-6 | -0.994575928740e-7 |
c4 | -0.499048287770e-8 | 0.318409457190e-9 |
c5 | -0.675090591730e-10 | -0.560728448890e-12 |
c6 | -0.574103274280e-12 | 0.560750590590e-15 |
c7 | -0.310888728940e-14 | -0.320207200030e-18 |
c8 | -0.104516093650e-16 | 0.971511471520e-22 |
c9 | -0.198892668780e-19 | -0.121047212750e-25 |
c10 | -0.163226974860e-22 | |
Exponential coefficients for temperatures above 0 °C | ||
a0 | 0.1185976 | |
a1 | -0.1183432e-3 | |
a2 | 0.1269686e+3 |
VOLTAGE OF DIFFERENT THERMOCOUPLES FOR A TEMPERATURE OF 350 °C
Voltage calculated in mV | |||
Type | By ITS-90 table | Voltage | Difference in % |
B | 0,596 | 0,596 | -0,018 |
E | 24,964 | 24,964 | 0,001 |
J | 19,090 | 19,090 | 0,002 |
K | 14,293 | 14,293 | 0,001 |
N | 11,136 | 11,136 | 0,002 |
R | 2,896 | 2,896 | 0,007 |
S | 2,786 | 2,786 | -0,008 |
T | 17,819 | 17,819 | -0,002 |