Resistance Temperature Detectors (RTDs)
RTD Types, Calibration
There are some excellent references online, but none seems totally complete simply because there are so many different types of device calibrations.
The Minco Products website has lots of very useful information in a pdf-format Technical Reference file. You can download it here. It contains technical detail about a number of RTD types including platinum (PRTs), copper and nickel.
An online resistance calculator is also located here and provides the temperature-resistance values for 23 different RTDs types, including some nickel and copper ones.
Burns Engineering Company has a downloadable RTD resistance Vs. Temperature calculator they call DINcalc (it’s a zipped file).
It is based on the 100 Ohm, 385 Temperature Coefficient Platinum RTD that is nearly a universal standard in the process control world. The German DIN standard DIN 751 for RTDs recognizes only platinum material with a temperature coefficient of resistance of 0.00385
Platinum RTD Output Equation
ASTM Standard E 1137/E1137M for Industrial Platinum Resistance Thermometers specifies that the resistance-temperature relationship for such devices for the range 0 °C to 650°C, to within the tolerances given below, will be described by the equation:
R(t) = R(0)[1 + At +Bt2]
Where:
t = temperature (to ITS-90), °C,
R(t) = resistance at temperature t,
R(0) = resistance at 0°C
A = 3.9083 * 10-3(°C), and,
B = -5.775 * 10-7(°C-2).
More details and the equation for -200 °C to 0°C as well as the inverse, temperature as a function of resistance are provided in the standard.
The standard is a copyright product of the ASTM and may be purchased at their website, www.astm.org.
In Europe, the German DIN standard, DIN EN 60751 (Industrial platinum resistance thermometers and platinum temperature sensors (IEC 60751:2008); German version EN 60751:2008) Standard , had been the major, recognised source for RTD properties.
Not withstanding this fact, the British have standard BS 1041-3 (BS 1041-3:1989
Temperature measurement. Guide to selection and use of industrial resistance thermometers). Both recognize the 0.003850 temperature coefficient for platinum RTDs.
Now the IEC administers the “DIN” standard as IEC Standard 60751.
The Callendar-Van Dusen equation and others are used to correct for the non-linearity of the resistance-temperature relationship for very high accuracy measurements, such as those performed in a metrology or calibration laboratory
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