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Different Types and Functions of Resistance Temperature Detector (RTD) Sensors

Temperature detection is an important element of many industries, allowing for the detection and/or tracking of various changes in settings, assemblies, or devices. One popular form of such technology is the resistance temperature detector (RTD) sensor, a type of passive temperature sensing device that relies on the principle that the electrical resistance of a metal will adjust in proportion to changes in temperature. As such, any electrical current sent through an RTD sensor will create a measurable resistance value that fluctuates based on temperatures. In this blog, we will discuss RTD sensors in more detail, allowing you to have a better understanding of what types exist and how they are used.

Depending on the application, temperature ranges, applicable standards, and other such factors, RTD sensors may be manufactured in a variety of ways. Nevertheless, all share the same basic function of measuring temperature through resistance. One of the main ways in which RTD sensors differ from one another is based on the element chosen as the sensing component, a few common options including platinum, copper, and nickel.

Platinum sensors are constructed with pure platinum wire, allowing them to have a positive temperature coefficient. With an optimal amount of linear and long-term stability, RTD sensors using platinum elements are known for being very accurate. In addition, those with copper wire extension leads can further benefit industrial applications where there may be a wide temperature range.

Nickel elements tend to be more limited in the range of temperature they can operate on, becoming non-linear when temperatures exceed 572 degrees Fahrenheit. This results in issues related to temperature processing and errors that will need to be corrected. While nickel elements suffer from such issues, they are known for being less expensive which can make them a suitable option for some needs.

With copper elements, good linear resistance is upheld across temperature changes, but they need a longer element than platinum options as a result of their low-resistivity forces. With the potential of copper oxidation, such elements should never be used in applications where temperatures exceed 302 degrees Fahrenheit. As such, they tend to be found within motors, generators, and turbines where they strike a balance between linearity and cost.

When it comes to RTD classification, categorization tends to depend on the construction of the temperature sensing element itself. While the most common options are thin film and wire wound, other types include coiled, PT100, PT1000, two-wire, three-wire, and four-wire variations. To determine which is best for your particular needs, you should consider your application, what temperature levels may be present, if there are any risks of corrosion or other environmental effects, and more.

Whenever an RTD sensor is installed within an assembly, it is important that it has a thermowell for more efficient heat transfer as it allows for such operations to be conducted without having to open a hole in the line. Many sensors will also have additional sheathing made from stainless steel or Inconel so that the sensing element can be safeguarded against any potential environmental effect or mechanical impact. While the sensor is able to conduct readings, it must be connected to a measurement recording device through termination wires.

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