Additel 221A Multifunction Temperature Calibrator User Manual - Manual (Page 56)

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9.4.3 Custom RTDs Library
The calibrator can measure temperature with most RTDs. But sometimes there is a need to support non‐standard RTDs
and Standard PRTs (standard platinum resistance thermometers).
The calibrator allows you to input the customized values, so you can measure temperature usingevery kind of RTDs and
Standard PRTs.
How to create a custom industry RTD?
To get high precision, IEC and ASTM standards specify a more complex polynomial that fine‐tunes the
resistance‐temperature relationship. One form of that equation is given here as below. The industry RTDs also specify
values for the constants R0, A, B, C (The C constant is only used for temperature less than 0℃).
1 100
For example, for the common Pt385 RTD with 100Ω resistance at 0 °C, the values are:
100Ω
A 3.9083 10
B 5.775 10
C 4.183 10
How to create a standard PRT?
The Standard Platinum Resistance Thermometer (SPRT) Calibration Laboratory of the NIST ThermometryGroup can
distinguish among the ITS‐90 from the argon triple point (Ar TP, –189.3442 °C) to the silver freezing point (Ag FP,
961.78 °C) for the calibration of SPRTs.
The ITS‐90 defines temperature through a set of specified thermometric fixed points, interpolation instruments, and