Temperature Measurement Using Thermocouple
Setup:
The setup consists of a shielded
K-type thermocouple, its signal conditioning unit, an immersion heater and a
beaker. The thermocouple has two terminals which are connected to the signal
conditioning unit. In the signal conditioning unit has a milli volt source that
provides -10 to +25 mV to calibrate the signal conditioner module for
measurement of temperature directly in oC. There is a zero and gain adjustment POT
provided for the calibration purpose. A 4 digit seven segment display is there for
displaying the output (mV or in degree Celsius) in digital form.
Working:
The thermocouple is immersed in a
hot water whose temperature is to be measured. The output of thermocouple is in
mV which is directly proportional to the temperature that the thermocouple
sense. The output of the thermocouple is connected to the signal conditioning
unit where it is directly fed to a DC differential amplifier and then is fed to
a summing amplifier. The summing amplifier has a gain and zero adjustment POT
to obtain output directly in engineering unit of temperature. An LM35 IC
temperature sensor is used for sensing ambient temperature that takes care of
the ambient temperature compensation.
Apparatus required:
Beaker with water.
An immersion heater
A thermometer
A multimeter
Procedure:
To get thermocouple output in mV:
Fill the water in beaker. Place
an immersion heater in the beaker and keep the thermometer as well as the
thermocouple in the beaker too.
Connect the output of the signal conditioner
with the DPM by a patch cord (between T2 and T3). Switch ON the power. Put the
toggle switch towards mV side. Set gain adjustment pot at anticlockwise i.e set
minimum gain. Short the input (Thermocouple) of the setup with a patch cord and
measure the output on DPM (Digital Panel Meter). It must be zero, if not adjust
it to zero with the help of zero pot. Remove the input short lead and connect
the I/P with a millivolt source having reading 10mV (measure with a
multimeter). The reading on DPM is in mV and set it to 10.00 with gain
adjustment POT. Remove the millivolt source from the input and connect the
thermocouple terminals. Switch ON the heater to heat the water. The millivolt
generated across the thermocouple terminals will be displayed on the DPM. Note
down the reading of both thermocouple and thermometer after a fixed time
interval. Plot the graph between temperature indicated by thermometer and
thermocouple emf(mV).
Observation:
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Sl no.
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Temperature
by thermometer
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DPM
reading (mV)
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To get thermocouple output
directly in degree Celsius:
Disconnect the thermocouple from
the input and short again by a patch cord. Toggle the switch towards oC. note down the
reading on DPM which is ambient temperature. Remove the short lead and connect
the millivolt source and set the value
at 4.1mV by multimeter. Adjust the DPM reading at 100+ambient temperature with
gain adjustment pot. Remove the millivolt source and connect the thermocouple
and note down the reading at different
temperature position by heating the water.
Observation:
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Sl no
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Temperature
by thermocouple
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Temperature
by thermometer
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TEMPERATURE MEASUREMENT USING RTD
Setup:
The setup consists of a RTD(Resistance Temperature Detector)
and its signal conditioning circuit. The RTD used here is a PT100 platinum RTD.
The RTD has been shielded by stainless steel so that it can be immersed in the
liquid or gas to sense the heat. The resolution of the RTD itself is 0.292 to
0.39Ω/oC. The temperature range that it can measure is -200 to 850 oC.
In the signal conditioning circuit there is a Wheatstone bridge, a differential
amplifier and an offset & gain adjustment circuit for calibration purpose.
Two switches are there named SW1 and SW2. There is a 3 ½ digit LED display to
display the temperature in oC, and some test points.
Working:
RTD is called Resistance Temperature Detector, whose resistance
changes with change in temperature. A two wire RTD called PT100 is used here,
PT100 implies that it has a resistance of 100Ω at 0oC. The RTD is
placed in a temperature changing environment whose temperature is need to be
measured. The two terminal of the RTD is connected to one arm of the Wheatstone
bridge. When its resistance changes due to change in temperature an unbalanced
output voltage is developed at the bridge output. This voltage is applied to a
differential amplifier and subsequently it is processed and calibrated to
display the temperature directly in oC.
Experiment 1: To study
the temperature Vs resistance characteristics of RTD (Pt100)
Apparatus Required:
RTD Pt100
Beaker
Thermometer
Heater
Water
Procedure:
Connect the wires of the RTD to the T1 and T2 terminals of
the RTDCC input block and switch ON the unit. Place the RTD, thermometer,
immersion heater in a beaker and pour water on it. Keep the switch SW1 in Right
direction. Place the multimeter in the resistance mode across T3 and T4. Switch
ON the heater power. Note the temperature in thermometer and corresponding
resistance value in multimeter. Plot the temperature Vs resistance graph.
Observation:
Sl no.
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Thermometer temperature in
( oC)
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Multimeter resistance (Ω)
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Experiment 2: To study
the temperature Vs voltage characteristics and the accuracy of the signal
conditioning board.
Apparatus required:
RTD Pt100
Thermometer
Immersion heater
Beaker
Water
Procedure:
Connect the wires of the RTD across T1 and T2 terminals of
the RTD input block. Switch ON the unit. Keep the switch SW1 in left direction
and switch SW2 in internal mode. Now adjust the Zero POT to match the thermometer reading on the display. This is done for initial setup of the unit and this adjustment
should be left undisturbed. Place
the multimeter in voltage mode across T6 and T7. Place the RTD, thermometer and
heater in the beaker and pour water in it. Switch on the heater power. Note
down the actual temperature in thermometer, output voltage across T6 and T7 and
temperature indicated by the display unit simultaneously. Plot the graph for
the actual temperature Vs Voltage. Calculate the error by this formula
% Error=Displayed
Temperature-Actual Temperature X 100
Actual Temperature
Plot the
graph for Temperature Vs %error.
Observation:
Sl no
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Actual Temperature(oC)
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Output Voltage(V)
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Displayed Temperature(oC)
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% Error
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