Resistance Temperature Detector

Resistance Temperature Detectors (RTDs) are precision temperature sensors that operate by measuring changes in electrical resistance of specific metallic elements as temperature varies. Essentially, RTDs determine temperature by correlating the resistance of the sensing element to the temperature value. A small current passes through a pure metal wire inside the sensor, and the resulting voltage, which changes proportionally with resistance, is measured and converted into temperature readings.

RTDs are constructed by either winding wire (wire-wound type) or depositing a thin metal film (thin-film type) onto a ceramic or glass core. This assembly is then sealed within a protective ceramic or glass capsule. They offer a broad temperature measuring range—typically from -50°C to 500°C for thin-film RTDs, and -200°C to 850°C for wire-wound RTDs—making the correct choice of sensing element and sheath material crucial for optimal performance.

Known for their high accuracy, stability, and repeatability, RTDs are widely used in both laboratory and industrial settings. Platinum is the preferred metal for RTD elements due to its excellent resistance to oxidation and corrosion, while alternatives like copper, nickel, and nickel-iron alloys are less common because of their limited temperature range and reduced stability.

RTDs are also less susceptible to electrical interference, which makes them particularly suitable for industrial environments near motors, generators, and other high-voltage equipment.

Various RTD configurations exist to meet specific application requirements, including:

RTDs with thermowells

Mineral insulated RTDs

Specialty/custom RTDs

When deciding between an RTD and a thermocouple, consider factors such as:

Required temperature range

Response time

Physical size constraints

Desired accuracy and stability