Download Temperature Measurement

Temperature
Measurement
Muhajir Ab. Rahim
School of Mechatronic Engineering
Universiti Malaysia Perlis
Introduction
• Almost all industrial processes need accurately
controlled temperature.
• It will determined the desired quality of products
(chemical, steel, plastic, nuclear and food industries)temperature dependent products and processes.
Temperature and Heat
• Temperature is the measure of the thermal
energy in a body, which is relative hotness or
coldness of a medium and is normally measured
in degrees, using Fahrenheit, Celsius and Kelvin
scale.
• Heat is a form of energy; as energy is supplied
to a system the vibration amplitude of its
molecules and its temperature increases.
Example unit of heat is BTU and calorie unit.
• The temperature increase is directly proportional
to the heat energy in the system.
Temperature Measurement
• Temperature measurement method can be broadly
classified as follows;
1) Non-electrical method
2) Electrical method
3) Radiation method
Non-electrical Method
• Example of non-electrical temperature measurement method;
1) Bimetallic thermometer
(based on the principle of solid expansion)
2) Liquid in glass thermometer
3) Pressure thermometers (based on the principle of fluid expansion)
low expansion material
high expansion material
Electrical Method
• Electrical methods are in general preferred for the
measurement of temperature as they furnish a signal
which can be easily detected, amplified or used for
control proposes.
• Example of temperature measurement by electrical
methods are;
1) Thermocouple
2) Resistance Temperature Detector (RTD)
3) Thermistor
4) IC Sensor
Resistance (R)
Voltage (V)
Thermocouple
RTD
Temperature (T)
Temperature (T)
Voltage or Current (V or I)
Resistance (R)
Temperature (T)
Thermistor
IC Sensor
Temperature (T)
RTD
Thermistor
IC Sensor
Radiation Method
•
•
The main advantages of
radiation method in
temperature measurement is
because of non contact with
the ubject of measurement.
So it is applicable to high
temperature, moving object..
Example of radiation method
temperature measurement
instrument is pyrometer.
How to select?
•
•
•
•
You need to consider several factors such as temperture range,
required range, accuracy, environment, speed of response, ease
of use and cost.
Thermocouple are used in high temp chemical industries such as
glass and plastic process.
Thermistor and IC sensor usually used in electronic hobby and
automotive industry.
RTD commonly used in lower temp., higher precision chemical
industries.