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Thermocouple and their Calibration

Thermocouple and their Calibration. Presented by. Rao Khaliq 2007-Chem-05. Temperature. Physical property of matter that quantitatively expresses the common notions of hot and cold. It is an intensive property. Why to measure temperature???.

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Thermocouple and their Calibration

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  1. Thermocouple and their Calibration

  2. Presented by • RaoKhaliq 2007-Chem-05

  3. Temperature • Physical property of matter that quantitatively expresses the common notions of hot and cold. • It is an intensive property.

  4. Why to measure temperature??? • It provides the driving force for heat flow. • It controls the reaction rates in process plant. • Temp above max. limits may cause safety problems.

  5. Temp Measuring Instruments • Thermistors. • Electrical Resistance Detectors (RTD). • Pyrometers. • Expansion of materials. • Thermocouples.

  6. What are Thermocouples???? • Thermocouple are devices used to measure the Temperature.

  7. How they work??? • Principle of working. “ Ajunction between two different metals that produces a voltage related to a temperature difference.” • This is also called the Seebeck effect after “Thomas Seebeck” who discovered this phenomenon.

  8. Seeback Effect • “When there is a difference in temperature between the two ends of circuit of two dissimilar metals, a small voltage is formed within the circuit.”

  9. Two Junctions • Hot Junction The junction that is put into the process in which temperature is being measured is called thehot junction. • Cold Junction The other junction which is at the last point of thermocouple material and which is almost always at some kind of measuring instrument, is called the cold junction.

  10. THERMOCOUPLE TYPES • Base Metals –up to 1000 Celsius • Type E • Type J • Type K • Type N • Type T • Noble Metals – up to 2000 Celsius • Type R • Type S • Type B • Refractory Metals –up to 2600 Celsius • Type C • Type G • Type D

  11. Votage to Temp. Conversion Charts

  12. Voltage to Temp Conversion Tables

  13. Selection of a Thermocouple • Factors to consider when selecting a Thermocouple: • Temperature Range • Media • Required Response Time • Accuracy • Measurement System Installation • Cold Junction Compensation • Leadwire Compatibility

  14. Time Response • The time response equates to how long it takes the TCs system to reach thermal equilibrium with the environment.

  15. Applications • Steel industry • Heating appliance safety • Thermopile radiation sensors • Manufacturing • Radioisotope thermoelectric generators • Process plants

  16. Thermocouple Calibration The equipment used: • Multimeter • Digital thermometer • Electrical device with a thermocouple • Thermo bath • Thermocouple table • Water

  17. How to Calibrate a Thermocouple?? • Heat the water filled bath to 30 degrees Celsius and turn the thermocouple device on. • Place one junction of the thermocouple into the water and allow the voltage to stabilize, Record the voltage from the multimeter. • Raise the water temperature to 35 C and record the voltage on the multimedia again. Repeat this procedure for each 5 C. • Repeat this procedure for each 5-degree increase in temperature from 35 to 60 degrees Celsius.

  18. Contt….. • Measure the room temp and look up the voltage for your thermocouple type at the room's temp. • Use the curve-fitting method of your choice to find the line that best fits your recorded data. • The slope of this line provides the voltage increase for each degree of temperature increase. • The voltage on a standard type K thermocouple should increase about 40 microvolts for every degree Celsius increase in temperature.

  19. The Advantages of Thermocouples • Self powered • Simple • Inexpensive and • Useful for wide Temperature ranges • Safety

  20. Thermocouples Disadvantages • Non-linear • Least sensitive and • Least stable • Measurement Errors • Corrosion

  21. Questions??????

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