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 wide selection of measuring ranges, 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:
RTD probes with IP66 NEMA 4X connection heads offering measuring ranges from -58 to 572 degrees F.
Spring-loaded probes ensure tip contact in thermowells for highly accurate temperature readings.
Heat Trace probes measure the surface temperature of process pipes to detect freeze-up or help maintain a viscosity level to ensure proper flow of the medium inside.
RTD probes with hex nipples allow easy probe replacement and connection to a junction box.
Spring-loaded RTD probes with hex nipples ensure tip contact in thermowells and allow easy probe replacement and connection to a junction box
Probes with an attached plug allow for quick and easy plug-in connections.
Probes with heavy-duty 6 ft. lead wire transitions allow easy connection to thermocouple extension wire.
RTD probes with integral M12 cable connections are perfect for attaching mating temperature transmitters.
Probes with sanitary connections are designed for applications where corrosion and product contamination are factors and are used extensively in the Food and Beverage industry.
Flange mount probes are ideal for use with ovens, freezers, ducts, or any application where through-the-wall temperature sensing is required.
Probes with cuttable lengths provide utmost flexibility and can be trimmed to the required length of a specific application.
Melt-bolt probes measure the melt temperature of plastic as it moves down the barrel of an extruder or injection molding machine.
Immersion RTDs are designed to be inserted into the medium being measured. Used throughout all industries but ideal for the plastics processing industry.
Bolt-on RTDs feature a ring terminal or washer and are bolt or screw mounted for surface temperature measurements.
Threaded bolt sensors are thread mounted and feature a 1/4-28 UNF threaded stainless steel rotating bolt for easy installation.
Wall-mount room temperature sensors (indoor ambient air temperature sensor) are appropriate for indoor use in offices, warehouses, manufacturing plant floor space, and walk-in freezers.
Sensors with a spade tip have an RTD sandwiched between two thin shims of stainless steel or sealed in epoxy between two layers of polyimide tape. Tip can be formed and secured to the outside of various size tubes, pipes, or nozzles.