How to use RTDs for Temperature Measurement – 8500917
Criteria for Temperature Selection of T/C and RTD Sensor Types
This is part two of a comprehensive three-part series that provides information for choosing an industrial temperature sensor from Thermocouple (T/C) and Resistance Temperature Detector (RTD) sensor types.
The Basics of Temperature Measurement Using RTDs
A Resistance Temperature Detector (RTD) is a passive circuit element whose resistance increases with increasing temperature in a predictable manner.
The traditional RTD element is constructed of a small coil of platinum, copper, or nickel wire. It is then wound to a precise resistance value around a ceramic or glass bobbin. The winding is generally done using one of two styles: birdcage or helix.
The birdcage winding keeps the platinum wire loosely wound on the bobbin. This allows it to expand and contract freely over temperature in order to minimize any stress-induced change in resistance. This style of winding is generally limited to laboratory use, as it has poor resistance to shock and vibration.
The helix wire-wound RTD uses a bifilar wound coil; wrapped around a bobbin and then sealed with molten glass, ceramic cement, or some other high-temperature insulating coating. The helix winding style helps protect the wire element from shock and vibration-induced changes to its resistance. However, it may still be prone to stress-induced resistance change; due to the different coefficients of thermal expansion of the wire coil and bobbin material.
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You can find the other whitepapers in this three part series in the links below: