Resistance Temperature Detectors (RTD's)

RTD’s are built from selected metals (typically Platinum), which change resistance with temperature change. The transducer is the temperature sensitive resistor itself, with the sensor being a combination of the transducer and electronics that measure the resistance of the device.

The resistance temperature detector (RTD) measures the electrical conductivity as it varies with temperature. The electrical resistance generally increases with temperature, and the device is defined as having a positive temperature coefficient. The magnitude of the temperature coefficient determines the sensitivity of the RTD. Apart from Platinum, other metals are used for RTD’s such as Copper and Nickel. Platinum is the most common and has the best linear characteristics of the three, although Nickel has a higher temperature coefficient giving it greater sensitivity.

The temperature coefficient defines how much the resistance will change for a change in temperature, and has units of ohms/o C. The greater the temperature coefficient, the more the resistance will change for a given change in temperature. This ultimately defines how sensitive the device is. RTD’s are generally quite linear, however the temperature coefficient does vary over the range of operation. As an indication, the temperature coefficient for Platinum is averaged at 0.00385 over the range from 0o C to 100o C, but varies by about 2% over this range.