Temperature Transducer

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Temperature Transducer

  1. 1. K.ARUNKUMAR AIT-07-002 Temperature Transducer
  2. 2. <ul><li>It is a temperature monitoring device. </li></ul><ul><li>The four most common temperature transducers: </li></ul><ul><li>the thermocouple </li></ul><ul><li>the RTD(Resistance Temperature Detector), </li></ul><ul><li>the thermistor and </li></ul><ul><li>the IC (Integrated Circuit) sensor </li></ul>What is?
  3. 3. Thermocouple <ul><li>Two dissimilar metals connected to form two junctions is called thermocouple . </li></ul><ul><li>The emf developed in the circuit is thermo electric emf. The current through the circuit is called thermoelectric current this effect is called thermoelectric effect or Seebeck effect . </li></ul>
  4. 4. <ul><li>In a Cu-Fe thermocouple the direction of the current is from copper to iron at the hot junction. </li></ul>
  5. 5. <ul><li>If the hot and cold junctions are interchanged, the direction of current also reverses . Hence Seebeck effect is reversible </li></ul>
  6. 6. Applications <ul><li>When one end (cold junction) is kept constant at a certain temperature, normally at 0°C, and the other end (measuring junction) is exposed to unknown temperature, the temperature at latter end can be determined by measurement of EMF so generated. </li></ul><ul><li>Three zones: </li></ul><ul><li>Uniformly hot zone </li></ul><ul><li>Varying zone </li></ul><ul><li>Uniformly cold zone </li></ul>
  7. 7. <ul><li>One of the main application of thermocouple is to find out the unknown temperature. </li></ul>Applications Thermocouple device
  8. 8. Standard thermocouple types <ul><li>They differ only by the way of pair of metals that forms the thermocouple. </li></ul><ul><li>Base metal type: </li></ul><ul><li>T,J,E,K,N </li></ul><ul><li>Nobel metal types: </li></ul><ul><li>S,R,B </li></ul>
  9. 9. Advantages <ul><li>Self powered </li></ul><ul><li>Simple </li></ul><ul><li>strong </li></ul><ul><li>Inexpensive </li></ul><ul><li>Wide variety of physical forms </li></ul><ul><li>Wide temperature range </li></ul>
  10. 10. Disadvantages <ul><li>Non linear </li></ul><ul><li>Low voltage </li></ul><ul><li>Reference required </li></ul><ul><li>Least stable </li></ul><ul><li>Least sensitive </li></ul>
  11. 11. RTD(Resistance Temperature Detector) <ul><li>An RTD is basically a temperature sensitive resistor. </li></ul><ul><li>It is a positive temperature coefficient device . </li></ul><ul><li>As like thermocouple it doesn't produce any voltage by itself. </li></ul><ul><li>It is used in electrical appliances such as motors, generators etc; </li></ul>
  12. 12. Tabulation <ul><li>The RTD is made from a pure material whose resistance at various temperatures has been documented. </li></ul>
  13. 13. <ul><li>When voltage is passed to the RTD connected device there is a voltage drop across the RTD element. </li></ul><ul><li>By that voltage drop the resistance of the RTD element can be easily determined. </li></ul><ul><li>Then by tabulating the resistance value in the table, the temperature of the device can be measured. </li></ul>
  14. 14. Two wired RTD circuit Three wired RTD circuit
  15. 15. Common Resistance Materials for RTDs <ul><li>Platinum (most popular and accurate) </li></ul><ul><li>Nickel </li></ul><ul><li>Copper </li></ul><ul><li>Balco (rare) </li></ul><ul><li>Tungsten (rare) </li></ul>
  16. 16. RTD elements <ul><li>The RTD element is the simplest form of RTD. </li></ul><ul><li>It consists of a piece of wire wrapped around a ceramic or glass core. </li></ul><ul><li>Because of their compact size, RTD elements are commonly used when space is very limited. </li></ul>
  17. 17. RTD thin film element <ul><li>A surface element is a special type of RTD element. </li></ul><ul><li>It is designed to be as thin as possible thus providing good contact for temperature measurement of flat surfaces. </li></ul>
  18. 18. RTD probe <ul><li>This is the most rugged form of RTD. </li></ul><ul><li>A probe consists of an RTD element mounted inside a metal tube, also known as a sheath. </li></ul><ul><li>The sheath protects the element from the environment. </li></ul>
  19. 19. Advantages RTD <ul><li>Most stable </li></ul><ul><li>Most accurate </li></ul><ul><li>More linear than thermocouple </li></ul>
  20. 20. Disadvantages <ul><li>Expensive </li></ul><ul><li>Slow </li></ul><ul><li>Current source required </li></ul><ul><li>Small resistance change </li></ul><ul><li>Four-wire measurement </li></ul>
  21. 21. Thank you

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