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Thermocouple as a Transducer


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General description of Thermocouples which are a type of thermo-electric Transducer.

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Thermocouple as a Transducer

  2. 2. Outline Thermocouples 2  Introduction  Principle  Description  Types  Applications  Advantages  Disadvantages
  3. 3. Transducer variations in a physical quantity another physical quantity in measurable form Thermocouples 3 Transducers are used in instrumentation systems to interface physical quantities with analytical ones.
  4. 4. Thermocouple • A thermoelectric transducer that converts heat directly into electricity, according to the Seebeck effect. • This can be used to generate electricity, measure temperature difference or change the temperature of objects. Thermocouples 4
  5. 5. The Seebeck Effect temperature difference between two junctions voltage difference between them which drives the current Thermocouples 5 Eemf = - S T where, S is the Seebeck coefficient = T1 – T2
  6. 6. Basic Thermocouple Circuit Thermocouples 6 If the SA and SB are constant for the given temperature range, then From Seebeck effect, the voltage gradient at any point in the circuit, Total measured end-to-end voltage between the junctions, Vb -Vc = (SA – SB) (Th -Tc ) = SAB (Th -Tc )
  7. 7. How it looks like ? Thermocouples 7 Its construction consists of two conductors, welded together at the measuring point and insulated from each other along the length, inside an outer protection sheath.
  8. 8. Types of Thermocouples Type K : Chromel-Alumel Type J : Iron-Constantan Type T : Copper-Constantan Type E : Chromel-Constantan Type N : Nicros-Nisil Type S : Platinum-Rhodium Type B : Platinum-Rhodium Type R : Platinum-Rhodium Thermocouples 8 There are many thermocouples, but only 8 of them are standardized internationally. BASE METAL NOBLE METAL Each thermocouple type has a specific range of temperature and environment.
  9. 9. Thermocouple EMF vs Temperature Thermocouples 9 This shows that the various thermocouples differ in their respective sensitivities.
  10. 10. Applications • Temperature Measurement • Power Generation • Radiation Sensors • Gas Safety Equipments • Manufacturing Industry Thermocouples 10
  11. 11. Advantages • Rugged • Inexpensive • Quick response time • Very simple in construction • Used to measure temperature ranges spanning thousands of degrees, around -200 C to 2200 C Thermocouples 11
  12. 12. Disadvantages • Low accuracy • Vulnerable to corrosion • Thermocouple operation is relatively complex with potential sources of error Thermocouples 12
  13. 13. THANK YOU Thermocouples 13