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Thermocouple - Electronic System Engineering

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Thermocouple - Electronic System Engineering Powered By Docstoc
					                     DEPARTMENT OF ELECTRONICS ENGINEERING
             MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO
                                      M.E, ESE

                                         Lab Experiment

PERFORMANCE OBJECTIVE
                  i.    To understand the purpose and types of Transducer.
                 ii.    To understand the Temperature transducer particularly thermocouple.
                iii.    Design a circuit with the aid of temperature transducer that monitors
                        the temperature of water.
EQUIPMENT
              Thermocouple
              Heat Bar (Complete Set)
              Oscilloscope
              Probes
              Multimeter

COMPONENTS
     i.        Bread Board
    ii.        TL 084 IC/ 741 IC
   iii.        Connecting Wires
   iv.         Resistors
INTRODUCTION
The input quantity for most instrumentation systems is non electrical. In order to use
electrical methods and techniques for measurement, manipulation or control, the non-
electrical quantity is converted into an electrical signal by a device called a transducer.
One definition states “a transducer is a device which, when actuated by energy in one
transmission system, supplies energy in the same form or in another form to a second
transmission system. This energy transmission may be electrical, mechanical, chemical,
optical or thermal.
Transducers may be classified according to their application, method of energy
conversion, nature of the output signal and so on. The passive transducers, produce
variation in some electrical parameter, but require external power to accomplish the task.
While the self-generating or active transducers produce an analog voltage of current
when stimulated by some physical form of energy, on their own. An example of active
thermal transducers is thermocouple, which provides voltage that is proportional to the
temperature difference of hot and reference junction.



THERMOCOUPLE



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               DEPARTMENT OF ELECTRONICS ENGINEERING
       MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO
                                M.E, ESE
When two different metals are brought into contact with one another, it is found that
electrons can leave one of the metals more easily than they can leave the other metal.
This is because of the difference in work function (energy required to take a free electron
out of metal) of two metals. Due to this shift, a potential difference exists between the
two metals; this e.m.f is called “Contact potential”.




If two metals are at the same temperature, the contact potentials cancel each other. Let
the metals be iron and copper, the current flows from copper to iron at the hot junction A,
and the arrangement is known as Thermocouple. The e.m.f. generated depend upon,
a) The pair of metals forming the thermocouple, and
b) The temperature difference between the two junctions.
                When copper and iron are placed in contact the potential of iron is above
that of copper as its temperature coefficient and resistivity are greater. At B current flows
form copper to iron i.e. from lower potential to higher potential and energy is absorbed
from the junction. At A current flows from iron to copper i.e. from higher potential to
lower potential and thus energy is given out so that the junction A is heated. Other
equivalent metals for copper and iron depending upon the type of material may be silver,
antimony, cadmium, etc and bismuth, cobalt, nickel, etc respectively.




According to the law of intermediate metals “any number of junctions may be introduced
into a circuit provided they are all at the same temperature”. This provides us the
capability to place the hot junction far form the meter and connecting the compensating
leads with the opposite ends without any error.




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                DEPARTMENT OF ELECTRONICS ENGINEERING
        MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO
                                 M.E, ESE
PROCEDURE
     i. Plug the heat bar, and give it at least 45 minutes to heat up.
    ii. Pour the water in the tank, and after the heat bar is reasonably hot place the
        water tank on notch 20 of heat bar.
   iii. First note the room temperature using thermometer, and then place
        thermometer in the tank. Also put the thermocouple (with red and black leads)
        into the tank where the space is provided.
   iv.  Wait up to 5 minutes so that the temperature becomes steady; note the water
        (thermocouple hot junction) temperature on the thermometer. Where the cold
        junction temperature is the room temperature.
    v.  Connect the DMM (millivolt scale chosen) to the leads of thermocouple and
        note the thermocouple voltage.
   vi.  Now move the tank to any other notch nearer to the supply end of heat bar,
        and repeat the process. Take at least five readings and fill the following table.

OBSERVATIONS

             Tank       Room        Temp      Thermocouple Amplified
     Notch Temperature Temperature Difference   Voltage    Output
        N          ( oC )             ( oC )           ( oC )            (VT)           Av=VA/VT




Note: VA is an amplifier output as you have connected any amplifier and VT is a direct thermocouple DC voltage
measurement that is input for amplifier.

LAB QUIZ
Q#1: - What is a Transducer? Differentiate b/w active and passive Transducers?
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Q#2: - What is the difference between a transducer and a sensor?
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Q#3: - What kind of Transducer is a thermocouple? What are its input and output?
________________________________________________________________________
________________________________________________________________________

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               DEPARTMENT OF ELECTRONICS ENGINEERING
       MEHRAN UNIVERSITY OF ENGINEERING & TECHNOLOGY, JAMSHORO
                                M.E, ESE
________________________________________________________________________
________________________________________________________________________
Q#4: - Mention at least three combination of metals normally used for a thermocouple.
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Q#5: - What are the industrial of thermocouple.
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ACTIVITY
      Design a circuit that amplify the output of the thermocouple in the range of
        Volts and then measure the variation of temperature with respect of water
        temperature.
      Draw a graph for the thermocouple voltage versus temperature.




PRECAUTIONS
       i. Don’t let the thermometer touch the bottom of the tank. It should be
          inserted up to the marked point.
      ii. Take readings after the temperature is stable, i.e take readings after five
          minutes of notch change.
     iii. Be cautious while handling the water tank, as it may be hot enough to
          cause any damage.
CONCLUSION
      Have you achieved the target mentioned in the Object?




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