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CHAPTER 4 TEMPERATURE MEASUREMENT, ELLIYA BT ROSLI 2018212678, How it…
CHAPTER 4
TEMPERATURE MEASUREMENT
4.1 INTRODUCTION
Temperature
is a measure of how hot or cold something is; specifically, a measure of the average kinetic energy of the particles in an object, which is a type of energy associated with motion.
The zeroth law of thermodynamic
If two bodies are in thermal equilibrium with a third body, then they are all in thermal equilibrium with each other
Example : THERMOMETER
TEMPERATURE SCALE
Fahrenheit , Celcius,
Kelvin=(T+273)
BIMETALLIC THERMOMETER
Bimetallic thermometers
are made up of bimetallic strips formed by joining two different metals having different thermal expansion coefficients.
1) Comprises of two metals which having different coefficient of thermal expansion(low and high expansion coefficient ), joint together to prevent the relative motion between it.
2) This two dissimilar metals,one is used for going temperature up and second is used for going temperature down
3) It expands with the increase in a temperature and it deflect the pointer which shows a reading on the scale
Advantage:
self generating type with low cost with no maintenance.
Disadvantage:
Inability to measure rapidly changing temperatures.
Thermocouple
Thermocouple
is a temperature-measuring device consisting of two dissimilar conductors that contact each other at one or more spots. 2
Thermocouple works on 3 basic effect:
1)Seeback effect
The amount of EMF generated is different for different combination of metal
2)Peltier effect
EMF is generated with the circuit due to the different temperature of two junction in the circuit
3)Thomson's effect
The potential difference exists in the circuit due to temperature gradient ,along the entire length of the conductor with in the circuit
1) If the temperature of both the junctions is same ,equal and opposite emf will be generated at both junction and the net current flowing through the junction is zero.
2) Since the two junction are maintained at different temperatures the Peltier emf is generated within the circuit and it is the function of the temperature of two junctions.
3) The voltage or current output obtained from thermocouple circuit give the value of unknown temperature directly.
Quartz Thermometer
Quartz thermometer
measures the temperature by measuring the frequency of a quartz crystal oscillator.The oscillator contains a specially cut crystal that the result in a linear temperature coefficient of frequency.
1) Piezo-electric crystal (quartz) provides a highly accurate and sensitive method of temperature measurement based on the change in its resonant frequency which is directly proportional to the temperature change. 2
2) To archive above properties the crystal is cut in the form of shear type LC (Linear coefficient) cut
3) The detection of change in frequency of oscillation of 1 Hz gives a resolution of 0.001° C, thus temperature in the range of -40 to 230°C can be measured precisely and accurately
ELLIYA BT ROSLI 2018212678
How it works?
How it works?
How it works??
