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Resistance temperature detectors

21st February 2013


Utilisation of resistance temperature detectors (RTD) has grown in lieu of thermocouples primarily in cold temperature applications. This has been driven by the availability of low cost reliable thin film RTD elements.

RTD's offer improved signal-to-noise ratio and increased immunity to EMI and do not require cold junction compensation compared to a thermocouple. Design engineers often do not consider application of RTD's at higher operational temperatures since these devices generally do not operate above 900°C and in many cases the higher operational temperatures cannot survive high vibration larger thermal cycle environments. This is a consequence of the grain growth of the wire element (generally platinum) at high temperatures. This results in a decrease in mechanical properties and increased sensitivity to chemical contaminants. Internal welds utilised in RTD construction are inherently weaker because of the grain growth induced from welding. Mitigating this effect requires a material that can maintain its structural integrity at higher operating temperatures. The development of a Metal Matrix Composite (SIMx) addresses these issues. It is composed of base material of transition metals reinforced with nano-oxides. These oxides are embedded within the lattice and grain boundaries of the material. These inhibit grain growth at elevated temperature. The integrity of the matrix is maintained which improves mechanical properties and chemical resistance. This core material is the basis of an RTD that is capable of withstanding vibration and thermal cycle loads in ground-based power generation systems.

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Harco is based in Branford, Ct. USA. www.harcolabs.com







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