An infrared thermometer is a new technological advancement in the field of temperature measurement which utilizes the thermal property of infrared light to measure temperature.Another term sometimes used for IR thermometer is laser thermometers because a laser is used to help aim the thermometer.
IR light have property of heating substance on which it is falling and every warm object emits it to some degree. By capturing this radiation and giving them to a detector proportional electrical energy can be generated for display.
They are very useful in many of the application where traditional temperature sensor like thermocouples,rtds etc are not so useful which for variety of reasons.
Field of view or distance to spot ratio
It is similar as the theangle of visiondefined for our eye but it is the angle for which the light can enter the sensor when aimed at target.It creates a spot at the target location depending ob the distance from the target.The target to be measure should completely fill this spot for accurate measurement.
Special laser is designed to help aim and judge the target being accurately covered within this field of view another term used is distance to spot ratio which is nothing but ratio of the distance from instrument to the object to the size of the spot being measured (D:S ratio) which is again approximately angles in radians The larger this ratio the better is the instruments resolution and smaller the spot size that can be measured
Emissivity is defined as the ratio of the radiation that is emitted by the substance to that emitted by perfe
ct black body at a given temperature.By that definition emissivity of perfect black body is 1.
IR thermometer will not be accurate unless it is set for the correct emissivity value of the target.
For instruments available with fixed sensitivity generally 0.95 correct reading can be observed by covering the substance with masking tape or flat black paint. And allowing it to reach the temperature of material underneath then measure temperature this will be the correct reading.Otherwise if the instrument emissivity is adjustable Some ways can be deployed to measure the emissivity value of the substance such as
Heating the substance at known temperature and then reading the temperature with ir instrument and matching it by changing the emissivity value.
Or drilling a hole in the substance of depth at least 6 times of diameter.This hole act as a black body measure temperature using IR instrument then match temperature at other location of substance by adjusting emissivity.It is generally suited fro high temperature body.
Standard emmisivity is also available for certain substance which can be directly entered.
How it works.
It consist of a lens to focus the radiation It is similar to an antenna which receives EM waves It then send these signal to a modulator which chops off unwanted interference signal.The modulator output is given to a detector .Now According to detection mechanism,they are divided into two type
:Photon detectors(works on the photoelectric effect)
They have high sensitivity and low respose time but require cooling mechanism for reducing noise.They are most commonly made of semiconductors whose electrons excitation is modulated by incident thermal energy causing change in resistance ( Photoconductive detectors)
Change in photoelectric current in pn junction .(Photo voltaic detectors)
Heat detectors(works on thermal effects.)
They work on change in property of substance on exposure to thermal energy examples include
Bolometer which changes resistance
And thermocouple thermopiles causing thermoelectric effect.
The detector output is processed into desirable analog output format for display device.
Infrared thermometers can be used to serve a wide variety of temperature monitoring functions. A few examples provided to this article include:
• cases dealing with moving objects ( i.e., rollers, moving machinery, or a conveyor belt),
• where non-contact measurements are required because of contamination or hazardous reasons (such as high voltage), electrical circuit breaker boxes or outlets for hot spots Detecting hot spots / performing diagnostics in electrical circuit board manufacturing
• where the object is surrounded by an EM field, as in induction heating;
• where the object is contained in a vacuum or other controlled atmosphere , for research and development or manufacturing quality control situations
• Applications where a fast response is required.
• where distances are too great, Detecting clouds for remote telescope operation
• where the temperatures to be measured are too high for other commonly used contact type sensors. Checking heater or oven temperature, for calibration and control purposes
• Monitoring materials in process of heating and cooling
Relate instrument using this technology are infrared cameras
They essentially measure temperature of much more point of relatively larger area to generate a two dimensional image called thermogram.Each pixel is representation of temperature of the mapped location in the image.They require larger processors and sophisticated software unlike spot IR thermometer.They can be used for perimeter monitoring in military.Quality monitoring in process control etc.