#Type j to type k thermocouple conversion how to#
#Type j to type k thermocouple conversion full#

#Type j to type k thermocouple conversion how to#

To learn more about cold junction compensation you can consult How To Do Cold Junction Compensation, and you can find the coefficients here: Where T CJ is the cold junction temperature, V CJ is the computed cold junction voltage, and the T 0, V 0, p i and q i are coefficients. To convert temperature to voltage, you can again use a rational function approximation of the form, Usually a range of -20 to +70☌ is sufficient. You don't need a valid equation for a wide temperature range as the cold junction is likely to be placed at ambient temperature. In that case you need the inverse transform, that is, an equation for converting temperature into voltage. You can then compute a cold junction voltage from that measured temperature, and use it to compensate the type K thermocouple voltage before converting the thermocouple voltage to a temperature. If so, you must measure the temperature of the cold junction using another sensor, perhaps a thermistor. Your type K thermocouple may be terminated at a cold junction temperature other than 0☌.

The following table contains calibration coefficients for Type K thermocouple wire. The coefficients, fitted data and charts of residual errors may be found in this Excel spreadsheet of K type thermocouple data.

#Type j to type k thermocouple conversion 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 K 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 K thermocouple data with a rational function of the following form,

The calibration equation uses a ratio of two smaller order polynomials rather than one large order polynomial. This page shows you how to convert type K thermocouple voltage to temperature with rational polynomial functions accurately and efficiently – more so than you can using NIST's higher order polynomials.Ī rational polynomial function approximation for Type K thermocouples is used for computing temperature from measured thermocouple potential.

However, the polynomial equations NIST provides aren't as accurate as they should be – they produce errors of fit as the high-order polynomial functions oscillate around the data, as shown in these curve fits of NIST polynomials to Type K thermocouple data.įortunately, there are more accurate ways to fit the data – using rational polynomial functions. NIST, the National Institute of Standards and Technology, provides a database of thermocouple values and a high order polynomial formula curve fitted to type K thermocouple data. However, if you are not using the Mosaic Thermocouple Wildcard, but looking for accurate equations for type K thermocouple measurement, we hope the type K thermocouple calibration coefficients and methods here are helpful.Įquations for voltage to temperature conversion usually use high order polynomials. Mosaic's Thermocouple Wildcard automatically converts measured voltages to temperatures for you, and with high accuracy.