Thermocouple Formulas

The output voltage from THERMOCOUPLE-1 is not directly proportional to temperature. The temperature from voltage output is calculated using a polynomial formula:

where d0 through dn are the coefficients of approximate inverse functions giving temperature as a function of the thermoelectric voltage and E is the thermocouple output voltage as given by the formula:

E = Vout / GAIN

Vout = Voltage Output from THERMOCOUPLE-1 Board

GAIN is fixed at 137 on THERMOCOUPLE-1 Board

For a J-Type Thermocouple in the temperature range of 0 to 760 degrees Celsius, the inverse coefficients are given as follows:

Coefficient Value
d0 0.000000
d1 19.78425
d2 -0.2001204
d3 0.01036969
d4 -0.0002549687
d5 0.000003585153
d6 -0.00000005344285
d7 0.000000000509989

Example: Voltmeter shows 367 millivolts at the output of THERMOCOUPLE-1 board. What is the temperature ?

Solution:

E = Vout / GAIN = 367/137 = 2.68 millivolts

So the thermocouple voltage is 2.68 millivolts.

Temperature = 0.00000 + 19.78425 X 2.68 - 0.2001204 X 2.68 X 2.68 + 0.01036969 * 2.68 X 2.68 X 2.68 - ... = 51.8 degrees Celsius

NOTE: Maximum measurable temperature using a J-Type Thermocouple and THERMOCOUPLE-1 Board is 529.7 degrees Celsius.