Most resistance temperature detectors (RTDs) consist of a fine wire (typically platinum) wrapped around a ceramic core, exhibiting a linear increase in resistance as temperature rises. With a measuring range of -58 to 572 degrees F, RTDs generally have higher accuracy and repeatability than thermocouples, but their response times are slower.
have a linear increase in resistance as temperature rises. RTDs come in 2-wire, 3-wire or 4-wire versions. A 2-wire RTD signal is affected by the distance to the controller. 3-wire or 4-wire RTDs can compensate for line losses.
have two dissimilar metal wires joined at the hot junction. As temperature changes, a millivolt signal is read at the cold junction. The most common types of temperature thermocouples are Type J thermocouples and Type K thermocouples. Advantages of thermocouple sensors include: low cost, small size, wider temperature ranges and faster response than RTDs. The disadvantages of using thermocouples include: they are less linear and accurate than RTDs, a matching extension wire is needed, and thermocouples are sensitive to electrical noise.
AutomationDirect offers a variety of RTD probes and sensors:
For indoor use to measure ambient air temperature.