
RTDs

Resistance Temperature Detectors (RTDs) are a type of temperature sensor that operates on the principle that electrical resistance of a material changes with temperature. The sensing element in RTD temperature sensors is typically made from a pure material, most commonly platinum, due to its linear resistance-temperature characteristics and its high positive temperature coefficient, meaning that its resistance increases with temperature.
There are two main types of RTDs: wire-wound and thin-film. Wire-wound RTDs consist of a fine wire wrapped around a ceramic or glass core. Thin-film RTDs, on the other hand, consist of a very thin layer (thin film) of platinum deposited on a ceramic substrate, forming a resistance wire in an electrical circuit pattern. Thin-film elements are generally more robust and less susceptible to mechanical strain than their wire-wound counterparts, and their manufacturing process allows for mass production, which makes them more economical.
RTDs have a wide temperature range and offer high accuracy for temperature measurements, which makes them ideal for a variety of industrial applications. They are, however, more expensive and complex to use than other types of temperature sensors, such as thermocouples.
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More Information about Resistance Temperature Detectors
An important consideration when using RTDs is lead wire resistance. Lead wires are used to connect the RTD sensor to the measuring instrument's sensor input, and their resistance can affect the accuracy of the temperature reading. This is particularly important in 2-wire configuration RTDs, where the resistance of the lead wires is in series with the sensor resistance and can cause a voltage drop that introduces error into the temperature measurement. To mitigate these effects, 3- or 4-wire configurations are often used, where the additional wires are used to compensate for the lead resistance.
The temperature-resistance relationship of an RTD is nearly linear over a limited temperature range. To ensure accuracy, the RTD resistance is typically calibrated at a common calibration temperature (like 0°C), and the temperature readings are corrected based on this calibration temperature.
FAQs
What is the measurable temperature range of RTD sensors?
Resistance Temperature Detectors (RTDs) can measure temperatures over a wide range, typically from around -200 degrees Celsius to +850 degrees Celsius, depending on the type of RTD and the specific design. However, the most common type of RTD, made from platinum (often referred to as a platinum resistance temperature detector), usually has a measurement range of -200 degrees Celsius to +600 degrees Celsius.
How does a resistance thermometer detect temperature changes?
A Resistance Thermometer, also known as a Resistance Temperature Detector (RTD), detects temperature changes based on the principle that the electrical resistance of a material changes with temperature. This relationship is typically positive and fairly linear, meaning that as temperature increases, resistance also increases.
What is an RTD?
What is an RTD?
RTD stands for Resistance Temperature Detector. RTDs use a specific type of metal that, depending on the resistance measured in the metal, can measure temperature. Thin film element RTDs use a very thin layer of resistive metal adhered to a substrate, typically ceramic, and coated in glass or epoxy. Wire wound element RTDs provide greater accuracy and a wider temperature measurement range, however, over time the element wire can become stressed leading to slight measurement errors. Coiled element RTDs are the most common type of RTD and allow for strain free measurement on the wire element while still providing accurate measurement.
How do RTD elements work?
As the temperature of a metal increases, the metal's resistance to the flow of electricity increases. As the temperature of the RTD resistive element increases, the electrical resistance, measured in ohms, also increases. Each metal has a certain resistance measurement at different temperatures. Based on the resistance that is measured in a given type of metal, it can be determined what the temperature is. The most common types of metals used in RTDs are platinum, nickel and copper.
What are some advantages and disadvantages of RTDs?
RTDs provide a high level of accuracy over a wide operating range. Because of their accuracy, they are often used in situations where temperature measurement is critical. RTDs are rarely used at temperatures above 660 degrees Celsius and they do not provide the same level of accuracy or resolution as thermistors at lower temperatures.