...
Introduction
A temperature sensor is a device that gathers data concerning the temperature from a source and converts it to a form that can be understood either by an observer or anther device. It measures the temperature of a medium. The sensors are used for different purposes from the simple home use to extremely accurate and precise scientific use.
...
Even human and most animals have biological temperature sensors in their body which works as the same function as the artificial does. It collects data and transfers it into a understandable form. For eg, human sensory nerves sends sensory information from the skin to the brain in the form of electrical impulses.
Types
Types: Temperature Sensors measure the amount of heat that produces from the object. It detects the changes of the temperature either as output of analog or digital. The temperature consists of two basic types of features:
...
These two basic types of sensors can be sub-divided into the following three groups of sensors, Electro-mechanical, Resistive and Electronic. All these are discussed below:
1. Thermostat
This is a type electro-mechanical temperature sensor, which is consists of two different types of metal; for example nickel, copper, tungsten or aluminum. These are bonded together to make a bi-metallic strip.
Figure: Working principle of bi-metallic Strip
http://www.electronics-tutorials.ws/io/io_3.html
...
Creeper types generally consist of a bi-metallic coil or spiral that slowly unwinds or coils-up as the temperature changes. Since,sensitivity depends on the length of the strip, this type of sensor allows for much greater sensitivity.
Advantages:
- Cheap to buy
- Portable
- Easy to install
Disadvantages:
- Does not give accurate result
- Slow to react to temperature changes
2. Thermocouple
Thermocouples are the most common temperature measuring device. It consists of two dissimilar metals, joined together at one end.
Working principle
Thermocouple works on the basis of Seebeck effect .If two conductors of different materials are joined at one point, an EMF is created between the open end which is dependent upon the temperature of the junction. As T1 increases, so does V. The EMF also depends on the temperature of the open ends T2. The junction is placed in the process, the other end is in iced water at 0C. This is called the reference junction. The voltage is directly proportional to temperature.
Types of thermocouple
...
http://www.thomasnet.com/articles/automation-electronics/Thermocouples-Types
Advantage
- It is simple and rugged in construction
- It can measure wide range of temperatures up to 2600°C
- Fast Response
- Inexpensive
- Calibration can be checked easily
Limitations
- It is least stable and least repeatable.
- It requires cold junction compensation for accurate temperature measurement.
- The emf induced verses temperature characteristics is non linear.
- Lowest accuracy.
Application
- Thermocouple is extensively used in steel processing, turbine and diesel engine for temperature measurement
- It is used in gas feed heat appliances such as ovens and water heaters.
- It is used in power production.
- A thermocouple can be used as a vacuum gauge over the range of approximately 0.001 to 1 torr absolute pressure
- Thermoelectric cooling
- Medical equipment and Packaging equipment
3. Thermistor
A thermistor is type of resistor whose resistance varies significantly with the temperature. They are widely used as inrush current limiters, temperature sensors, self-resetting overcurrent protectors and self-regulating protectors.
...