Where a thermocouple senses temperature as a function of the voltage generated from the difference in temperature between the open and closed ends, a Resistance Temperature Detector (RTD) senses temperature as a result of the change in resistance that occurs when it changes temperature.
Platinum is the material used in most RTD's. It is highly resistant to contamination and has a predictable resistance change as a function of temperature. Classically, platinum wire is wound around a ceramic bobbin.
Other materials used in RTD's are tungsten, copper, nickel and nickel alloys. The common characteristic of most of these materials, including platinum, is high resistivity (copper is the exception). The higher the resistivity, the less metal that needs to be used. Because of its stable and predictable characteristics, platinum is the first choice for use in RTD's.
Some RTD's are constructed by depositing a platinum film on a substrate. It is then encapsulated for protection. Because these thin-film devices are small, they respond rapidly to changes in temperature.
RTD temperature measurements might be made by measuring the resistance of the sensor and using that reading to determine its temperature. Because the resistance of an RTD is quite low, however, the resistance of the wires connecting the RTD to the meter can be significant. To eliminate the error introduced by the lead resistance, a Wheatstone Bridge or similar circuit is used. When the RTD is connected in this manner, it is possible to read only the resistance of the RTD. This is why most RTDs have three or more leads. Unless otherwise stated, all Love Controls RTDs are made for three wire operation.
In the bridge circuit, the RTD is one resistor in the group of resistors which comprise the bridge. A small regulated current, sometimes known as a "search current" is transmitted through the device. At a constant current, the voltage measured across the bridge will vary with the resistance and provide a value that can be interpreted as temperature.
RTD's are generally less rugged and more expensive than other sensors. They offer, however, higher accuracy (typically ±0.10% of reading), repeatability and long-term stability.
RTD's are typically used in food, laboratory and pharmaceutical applications, and in other applications requiring high accuracy.
All Love RTD's are manufactured to industry standards and meet stringent ANSI standards. This assures interchangeability with other standard RTDs without requiring additional instrument recalibration.
Love RTD's are used in all types of applications, can measure wide temperature ranges, and are offered in a large variety of standard configurations.
All Love RTD assemblies are designed for process temperatures up to 850ºF (500ºF for teflon wire). If higher service temperatures are required, please consult the factory. See Applications Guidefor additional information