INFRARED THERMOMETER

 

Nowadays the infrared temperature sensor is commonly seen in all the places which is used to measure the temperature of a person. The infrared temperature sensor is a type of contactless type where we can able to measure the temperature without any contact. The laser is used in these types of sensors so they are also known as the laser thermometers.

WORKING PRINCIPLE:

            The heat transfers from a body in three modes they are:

·                                 * CONDUCTION

·                                 * CONVECTION

·                                                  * RADIATION

 

* CONDUCTION: Transfer of heat energy through direct contact

* CONVECTION: Transfer of heat energy through the movement of liquid or gas

* RADIATION: Transfer of heat energy through the thermal emission.  

This sensor works on the principle of black body radiation. For example when a body is exposed to an INFRARED RADIATION some amount of energy is absorbed by the material and some amount of energy is reflected back by the material. This depends on the type of the material i.e. rough surface have low reflectivity and the polished surface have high reflectivity, In the state of thermal equilibrium the amount of energy absorbed by the body is emitted  by the body. But the black body is one which absorbs all the energy and does not have any reflection; they are commonly called as GRAY BODIES, so the black body also emits the energy absorbed by it. In the case of black body it absorbs all the energy that falls on it as a result it emits all the energy which is absorbed by it. So the amount of energy emitted by the body is greater than that of the normal type of body.

 

COMPONENTS OF IR THERMOMETER

·                                * OPTICAL COMPONENTS

·                                 *  IR DETECTOR

·                                 * ELECTRONICS

·                                * DISPLAY

OPTICAL COMPONENTS:

In this case the optical component used is a lens which is used to focus the energy on the IR sensor. Based on the amount of energy focused the temperature also changes so the lens plays an very important role in the measurement of the temperature and the another factor is that if the lens is get dirty the amount of energy focused also varies which results in change in the temperature value. And in the same time the detector which is used should be protected from various damages which will ne accidently caused so a zinc sulfide glass is used for long range detectors, germanium glass is used for short range detectors and quartz is used for mid-range detectors.    

IR DETECTOR:

IR detector can be single wavelength or dual wavelength. In the case of single wavelength it detects only the wavelength within the range but the dual wavelength type can sense the wavelength of multiple ranges.

The IR detectors can be classified into two types

* Thermal detectors 

* Photo detectors

1.      THERMAL DETECTOR: 

            The thermal detectors are classified into three types they are: 

   * Thermopiles- generate thermoelectric voltage

    * Pyroelectric-  they change the polarization   

   * Bolometer- they change the resistance                          


 

Commonly the thermopiles are used in these IR thermometers. The thermopile consists of several thermocouples connected in series which are placed in contact with the blackbody. These detectors are very fast and have very large range of sensing and are very accurate. 

2.      PHOTO DETECTORS:

The photo detectors are made on a silicon substrate in which the free electrons are released when they come in contact with the photons. So as the temperature increases the amount of electrons emitted will be less. 

ELECTRONICS:

The electronics used in this are:

* HIGH-GAIN AMPLIFIER

* SIGNAL CONDITIONING CIRCUIT 

* ANALOG TO DIGITAL CONVERTER 

1.      HIGH-GAIN AMPLIFIER:

An operational amplifier without any feedback is known as high-gain amplifier, but an amplifier without any feedback of waste, but with the correct feedback it results in input voltage equal to the output voltage. So this results in the very less consumption of current from the circuit, so the losses will be less. The high gain amplifier is used to provide more amount of signal without any losses.

2.      SIGNAL CONDITIONING CIRCUIT:

The signal conditioning circuit is used to convert a signal into higher level of electrical signal. The main function is to convert a difficult signal into a readable signal by a conventional circuit. It is also used to protect the equipment and the personnel from the power failure. When a power failure occurs a pulse of high voltage enters into the measuring circuit, which will damages the circuit. So it prevents by using a galvanic isolation.

.          ANALOG TO DIGITAL CONVERTER:

It is commonly used to convert analog signal into digital signal.     

  WORKING:

 

                When the sensor is placed in the forehead of a person or at any material due to due to the black body radiation the heat is captured which is focused by the lens used in the instrument. Due to the use of lens more amount of the energy will be focused. The focused energy is transferred to an element known as the thermopile. As known the thermopile is an electronic circuit which converts the thermal energy into electrical energy i.e. in the form of voltage. Next to the thermopile the high gain amplifier is used which will help in reducing the losses, and very less consumption of the current from the circuit. Next a signal conditioning circuit is used which will convert the voltage onto a higher level of voltage, and also protects the circuit from the electrical faults. Then the signal goes to the ADC which converts the analog signals into digital signals which are shown as the output by using the digital display.

 

CONCLUSION:

                By using the INFRARED TEMPERATURE SENSOR the temperature of a person can be easily obtained without any contact. The main advantage is that they are very fast in their operation which makes them very reliable, but the main disadvantage is that their accuracy is only 97% which tells that they can also read the temperature wrongly. This situation happens when a person is holding an object, in this case the IR SENSOR can wrongly sense the temperature of the object which is held by the person.