RTD Sensors Made Easy. What is an RTD Sensor?

RTD's. What are they? What are they used for? How do they work? What is the difference between a 2-wire & 3-wire configuration?

What are RTD temperature sensors?

RTDs, or Resistance Temperature Detectors, are a very common type of temperature sensor known for their accuracy, stability, and repeatability characteristics.

Where are RTD temperature sensors Used?

RTD sensors are used in many industrial, scientific and OEM applications found in nearly all markets, such as water treatment plants, food processing equipment, medical research & development, and pharmaceutical manufacturing to name a few.

How do RTD temperature sensors work?

Within an RTD temperature sensor is an RTD element.  The element operates by measuring the change in resistance of a thin wire wound on an insulated form or coiled up in a self-supporting structure. Most often the wire is made of pure or slightly doped platinum, a material that exhibits a very stable and linear change in resistance over a wide range of temperatures.

The vast majority of RTD temperature sensors in commercial use are known as Pt100 sensors, which indicates that they use a platinum element with 100 Ohms resistance at 0°C.

Other less common types of RTD temperature sensors may use a Platnum1000, Copper50, or Nickel100 element, to name a few.

What is the difference between 2 and 3 wire configurations?

While the element itself only requires 2 connections, the actual RTD hook up may utilize 2 or 3 lead wires.

The drawback of the simple 2-wire connection is that, in addition to the measuring the resistance of the element, the R1 & R2 lead wires also have a resistance, which can introduce offset errors into the measurement.

As a result, a 2-wire RTD connection is mostly used in applications where the lead wires are very short, or if the measurement accuracy and precision are not critical.

The 3-wire RTD connection is far more common. The resistance of the element including the R1 & R2 lead wires are measured.  Then the resistance is also measured through the R2 & R3 lead wires.  This allows the measuring instrument to account for the resistance of the lead wires, thereby allowing a more accurate temperature measurement to be calculated.