If so, you must measure the temperature of the cold junction using another sensor, perhaps a thermistor. Your type T thermocouple may be terminated at a cold junction temperature other than 0☌. The following table is of calibration coefficients for Type T thermocouple wires. The rational function approximation interpolates the data well so that computed values of temperature are more accurate than the residuals plots would indicate. Most of the residual error results from rounding of the NIST provided voltage values to the nearest microvolt. The graph shows residual errors after calibrating the thermocouple with a rational function of polynomials. The following table contains calibration coefficients for Type T thermocouple wire. The coefficients, fitted data and charts of residual errors may be found in this Excel spreadsheet of thermocouple data.
#Millivolt to temperature conversion chart full
The full temperature range is broken into several sub-ranges, and a different set of coefficients used for each. The coefficients, T o, V o, p i and q i were found by performing a least squares curve fit to the NIST data for type T thermocouples. The second form of the equation emphasizes the most efficient order of operations. The function uses a ratio of two polynomials, P/Q, in this case a fourth order to a third order polynomial. Where T is the thermocouple temperature (in ☌), V is the thermocouple voltage (in millivolts), and T o, V o, and the p i and q i are coefficients. Using a least squares curve fitting procedure we fit the National Institute of Standards and Technology (NIST) type T thermocouple data with a function of the following form, The calibration function uses a ratio of two smaller order polynomials rather than one large order polynomial. The rational polynomial coefficients for type T thermocouples provided here exhibit an order of magnitude lower errors than the type T NIST ITS-90 thermocouple coefficients, for both direct and inverse conversion.Ī rational polynomial function approximation for Type T thermocouple data is used for computing temperature from measured thermocouple voltage (potential). This page provides those functions and coefficients so you can convert thermocouple voltage to temperature (for measurement) and temperature to voltage (for cold junction compensation) accurately and efficiently. The data can be fit with much lower errors using rational polynomial functions. However, their high order polynomials are often not very accurate – they show systematic errors because the polynomial functions weave around the desired data, as shown by these curve fits to Type K thermocouple data. For example, the National Institute of Standards and Technology ITS-90 database of thermocouple values publishes a high order polynomial formula with coefficients for voltage-to-temperature conversion. If you are using other hardware and are looking for equations to accurately convert type T thermocouple to voltage, we hope the type T thermocouple calibration equations and coefficients on this page will be helpful.įunctions for voltage to temperature conversion often use high-order polynomials. If you are using the Thermocouple Wildcard, type T voltage measurements are automatically converted to temperatures for you.
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