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Thermocouples

Sohaib Hasan. Thermocouples. THERMOCOUPLE. Invented by Thomas Johann Seebeck in 1821 Converts Thermal Potential Difference to Electrical Potential Difference. OPERATION.

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Thermocouples

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  1. Sohaib Hasan Thermocouples

  2. THERMOCOUPLE • Invented by Thomas Johann Seebeck in 1821 • Converts Thermal Potential Difference to Electrical Potential Difference

  3. OPERATION • When two dissimilar metals are joined at both ends and one end is heated, there is a continuous current which flows through the circuit. Metal A X Y Metal B Seeback Voltage eAB = αΔT

  4. SELECTING A THERMOCOUPLE • Style • Joints • Type • Sheath Metal • Junction • Length • Diameter

  5. THERMOCOUPLE STYLES • Beaded Wire • Surface Probe • Thermocouple Probe

  6. THERMOCOUPLE JOINTS • Transition Joint • Molded Junction • Rugged Junction • Industrial Head • Cast Iron Head • Aluminum Head

  7. THERMOCOUPLE JOINTS • Quick Disconnect • Standard • Mini • Ceramic • Ceramic Mini • Handle Probe

  8. TYPES Al: Aluminum Cr: Chromium Cu: Copper Fe: Iron Mg: Magnesium Ni: Nickel Pt: Platinum Re: Rhenium Rh: Rhodium Si: Silicon W: Tungsten

  9. SHEATH METAL • Stainless Steel • Inconel

  10. LENGTH & DIAMETERS • Standard Lengths • 6” • 12” • 18” • 24” • Custom • Standard Diameters • 0.010” • 0.020” • 0.032” • 0.040” • 0.062” (1/16”) • 0.125” (1/8”) • 0.1875” (3/16”) • 0.25” (1/4”)

  11. JUNCTION • Grounded • Ungrounded • Exposed

  12. COLD JUNCTION COMPENSATION (CJC) • In order to get accurate temperature, the reference junction should be at 32oF (0oC). • If the temperature at X is desired, temperature at Y should be 32oF to get accurate ΔT. Metal A X Y Metal B Seeback Voltage eAB = αΔT

  13. CJC CORRECTION • Placing junction at 32oF • Hardware Correction • Software Correction X Y

  14. TEMPERATURE vs. VOLTAGE

  15. REFERENCES • www.omega.com • www.temperatures.com • en.wikipedia.org/wiki/Thermocouple • www.m-system.co.jp • www.megatron.co.il/Thermocouple.html

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