Resistance temperature detectors (RTDs), also known as resistance thermometers, accurately sense process temperatures with an excellent degree of repeatability and interchangeability of elements. They provide higher accuracy than thermocouples in their temperature range because platinum is a more stable material than are most thermocouple materials. RTD’s also use standard instrumentation wire to connect to the measurement or control equipment.
Thermocouples are the most common, convenient, and versatile devices used to measure temperature. They convert units of heat into useable engineering units that serve as input signals for process controllers and recorders. Thermocouples are generally less expensive than RTD’s, they are more durable in high vibration or mechanical shock applications and are usable to higher temperatures. Thermocouples can be made smaller in size than most RTD’s so they can be formed to fit a particular application.