RTDs (Resistance Temperature Detectors) are temperature detecting devices that vary their resistance value when surrounding temperature changes. RTD sensing elements use well-known materials that change resistance in a predictable and repeatable manner. Their popularity and general use are outcomes of the RTD's predictability and stability.
The most common type and material of RTD is the 100-ohm platinum sensor. Its use is ubiquitous in the laboratory and industrial process applications going back many decades. The precision, reproducibility, and stability of 100-ohm platinum RTDs (PT100) are well known.
For the most part, resistance temperature detectors (RTDs) fall into two main categories. Thin-film elements are one form of RTD, and wire-wound elements are the other. Each type provides advantages in certain situations and purposes. The more common design, wire-wound, is a length of tightly coiled wire wrapped around a ceramic or glass bobbin. Because the wire and wrapping are delicate, it is usually enclosed in an encased metallic tube to protect them from stress and vibration.
The 100-ohm platinum RTD provides accurate temperature readings with excellent stability and repeatability. They are also very resistant to electrical noise, making them ideal for temperature monitoring in industrial facilities near motors, generators, and high voltage equipment.
The American and European (known as the DIN or IEC standard) 100-ohm platinum RTD standards are the same, with the IEC standard considered the default for PT100. According to the IEC751 standard, the RTD must have:
- The electrical resistance of 100.00 O at 0°C
- A TCR (temperature coefficient of resistance) of 0.00385 O/O/°C between 0 and 100°C.
Because resistance is used to measure temperature in 100-ohm platinum RTDs, the lead wires, connections, and measurement devices contribute extra resistance, requiring external compensation to offset the error. A solution is found by inserting a third or fourth lead wire inversely proportional to the external resistances.
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