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Understanding Infrared Thermography Reading 3

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3.2 Contacting Thermal Measuring Devices<br />

The most commonly used contacting devices include bimetallic thermometers,<br />

thermochromic liquid crystals, thermocouples, resistance thermometer,<br />

thermistors and heat flux indicators. These devices are discussed briefly here.<br />

For more detailed information, refer to ASNT Nondestructive Testing<br />

Handbook. third edition: Volume 3. <strong>Infrared</strong> and Thermal Testing.<br />

■ Bimetallic Thermometers<br />

Bimetallic thermometers are sensors constructed of dissimilar metallic strips<br />

bonded together. Typically. different iron nickel alloys are used. The strips<br />

differ in temperature coefficient of expansion such that temperature changes<br />

result in predictable bending of the assembly. Arranged in a spiral or helical<br />

configuration. one end of the bimetallic element is fixed and the other end is<br />

attached to a pointer. Properly calibrated, the angular position of the pointer<br />

can be made to indicate temperature on a scale.<br />

Charlie Chong/ Fion Zhang

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