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Tables and polynomials

Tables and polynomials for thermocouples and Pt100

RTD tables:

Thermocouple tables:

All tables collected

 

Guide to the use of the tables

Thermocouples

The tables show the output signal of the thermocouple as a function of the measuring junction temperature. The reference junction is supposed to be at 0 °C. Most temperature indicators perform that measurement of the reference temperature internally.

If the output signal is measured with a voltmeter which has no internal compensating circuits for the actual reference junction temperature the voltmeter will present the differential temperature between measuring and reference junctions.

Example: With a type K thermocouple connected to a plain microvoltmeter you are measuring 100 °C in 20 °C room-temperature. According to the Type K table the temperatures equal 4096 µV and 798 µV respectively. The difference is 3298 µV which is shown in the voltmeter display. If you compare the difference to the table value of 80 °C you will find a slightly different number, 3267 µV, which depends on the non-linear voltage-temperature function. To obtain correct result the rule is to add the room-temperature to the measured value.

The non-linearity is indicated in the righthand part of the columns by the Seebeck coefficient which is measured in µV/°C for each ten-degre level of temperature. For thermocouple K the coefficient varies around 40 µV from 0 to 1000 °C. Above, it will be less. The Seebeck coefficient is used to interpolate in the gaps between the tabulated temperatures.

Above the tables you will find the polynomials used to calculate the emf-voltages for each temperature. The polynomials are experimentally derived and the more winding a function is the more high-order terms are needed to follow the turns. Type K even needs a special exponential term to track som irregularities of its temperature-emf function. IEC 60751 also contains the experimentally derived reverse functions.

RTD Pt100

The table shows resistance as function of temperature. As an example the resistance at 100 °C is 138,506 ohms. In the right-hand side of the columns dR/dT is shown which is the sensitivity at the actual temperature interval. Thus at 100 °C dR/dT is 0,0739 ohms/°C. The function is slightly non-linear.

The sensitivity value can be used for interpolation inbetween the tabulated temperatures.