The document discusses different types of temperature transducers, focusing on thermocouples and RTDs. It provides details on how thermocouples and RTDs function to measure temperature, their common applications, advantages and disadvantages. Specifically, it explains that thermocouples use the Seebeck effect to generate voltage based on a junction of two dissimilar metals, while RTDs measure the change in resistance of materials like platinum as their temperature varies. It also lists standard thermocouple types and common resistance materials used for RTDs, as well as different forms that RTDs can take like probes.

1. K.ARUNKUMAR AIT-07-002 Temperature Transducer

2. It is a temperature monitoring device. The four most common temperature transducers: the thermocouple the RTD(Resistance Temperature Detector), the thermistor and the IC (Integrated Circuit) sensor What is?

3. Thermocouple Two dissimilar metals connected to form two junctions is called thermocouple . 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 .

4. In a Cu-Fe thermocouple the direction of the current is from copper to iron at the hot junction.

5. If the hot and cold junctions are interchanged, the direction of current also reverses . Hence Seebeck effect is reversible

6. Applications 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. Three zones: Uniformly hot zone Varying zone Uniformly cold zone

7. One of the main application of thermocouple is to find out the unknown temperature. Applications Thermocouple device

8. Standard thermocouple types They differ only by the way of pair of metals that forms the thermocouple. Base metal type: T,J,E,K,N Nobel metal types: S,R,B

9. Advantages Self powered Simple strong Inexpensive Wide variety of physical forms Wide temperature range

10. Disadvantages Non linear Low voltage Reference required Least stable Least sensitive

11. RTD(Resistance Temperature Detector) An RTD is basically a temperature sensitive resistor. It is a positive temperature coefficient device . As like thermocouple it doesn't produce any voltage by itself. It is used in electrical appliances such as motors, generators etc;

12. Tabulation The RTD is made from a pure material whose resistance at various temperatures has been documented.

13. When voltage is passed to the RTD connected device there is a voltage drop across the RTD element. By that voltage drop the resistance of the RTD element can be easily determined. Then by tabulating the resistance value in the table, the temperature of the device can be measured.

14. Two wired RTD circuit Three wired RTD circuit

15. Common Resistance Materials for RTDs Platinum (most popular and accurate) Nickel Copper Balco (rare) Tungsten (rare)

16. RTD elements The RTD element is the simplest form of RTD. It consists of a piece of wire wrapped around a ceramic or glass core. Because of their compact size, RTD elements are commonly used when space is very limited.

17. RTD thin film element A surface element is a special type of RTD element. It is designed to be as thin as possible thus providing good contact for temperature measurement of flat surfaces.

18. RTD probe This is the most rugged form of RTD. A probe consists of an RTD element mounted inside a metal tube, also known as a sheath. The sheath protects the element from the environment.

19. Advantages RTD Most stable Most accurate More linear than thermocouple

20. Disadvantages Expensive Slow Current source required Small resistance change Four-wire measurement

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