Number of FAQs related to Terminal Input Modules: 1
"PRT" refers to "Platinum Resistance Thermometer." PRTs use a bridge measurement (a three- or four-wire half-bridge or a four-wire full-bridge) to measure temperatures. Just as any other resistive materials, platinum has a variable resistance depending on the temperature of the surrounding area and on the length of the platinum.
The resistive variability measurement is expressed as Temperature Coefficient of Resistivity. The low Temperature Coefficient of Resistivity value of platinum means that its resistance variability does not swing as widely as many other metals, hence its use.
Platinum's variability of resistance because of temperature is reproducible (most metals have this reproducibility), so the thermometer uses resistive measurements. A fifth-order polynomial is used to increase the accuracy of the correlation between the temperature change and the corresponding resistance change on platinum because the variability of resistance is reproducible, but it is not linear with temperature change.