REDwire RTD, thermocouple or thermistor: Which temperature sensor is right for you?

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Are you trying to decide which temperature sensor is the right fit for your application?

Are you trying to decide which temperature sensor is the right fit for your application? This article takes a look at the advantages of resistance temperature detectors (RTD), thermocouples and thermistors, to help you determine the best solution for your needs.

Resistance temperature detectors: An RTD sensing element consists of a wire coil or deposited film of pure metal. The element’s resistance increases with temperature in a known and repeatable manner. RTDs exhibit excellent accuracy over a wide temperature range, and represent the fastest growing segment among industrial temperature sensors. Their advantages include: a temperature range from -260 to 850 degrees C; repeatability and stability; sensitivity (the voltage drop across an RTD provides a much larger output than a thermocouple); linearity (platinum and copper RTDs produce a more linear response than thermocouples or thermistors); low system cost; and standardization (manufacturers offer RTDs to industry standard curves). 

Thermocouples: A thermocouple consists of two wires of dissimilar metals welded together into a junction. Though thermocouples are simple and familiar, designing them into systems is complicated by the need for special extension wires and reference junction compensation. Their advantages include: extremely high temperature capability (rated as high as 1,800 degrees C); resistance to shock and vibration; and small size and fast response. 

Thermistors: A thermistor is a resistive device composed of metal oxides formed into a bead and encapsulated in epoxy or glass. A typical thermistor shows a large negative temperature coefficient. Resistance drops dramatically and non-linearly with temperature. Sensitivity is many times that of RTDs, but useful temperature range is limited. Their advantages include: low sensor cost (basic thermistors are quite inexpensive, but models with tighter interchangeability or extended temperature ranges often cost more than RTDs); high sensitivity (can change resistance by tens of ohms per degree temperature change, versus a fraction of an ohm for RTDs); and a thermistor bead can be made the size of a pin head for small area sensing.

For more information, contact Mod-Tronic, the Brampton, Ont.-based distributor of MINCO temperature sensors.

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Mod-Tronic Instruments Ltd.

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