Contactless thermometers - in general
Among the advantages, that have not been mentioned yet, belongs fast measuring, when the temperature appears within 0.5 seconds on the display. Contactless thermometers are also great for measuring high or low temperatures, which can not be measured by common thermometers. It does not affect the measured object, the measuring takes place without any risk of contamination and mechanical effects on the surface of the measured device.
How does the measuring work?
Infrared radiation is vibration with wavelength over 750nm. Infrared radiation creates the source of warmth for planet Earth. In case it is absorbed by living organisms, earth or atmosphere the infrared radiation changed into heat. Light, which is eye visible, has wavelegth 380nm up to 750nm.
Each material radiates energy in the form of infrared radiation, which creats heat. If the measured object does not have the same temperature as its surroundings, it is possible to measure the temperature. Infrared light works in the same way as eye-visible light, which can be localized, reflected or absorbed.
Manual infrared thermometers usually use objective lens for concentration of the infrared light from one object to the detector (termopile). The detector absorbs infrared radiation and converts it to the heat. The more infrared energy there is, the more heat is created, which is then converted to electricity, which is then on the detector determins the temperature of the object onto which the thermometer was pointed.
What is emisivity
Materials have various radiations at various emisivities. The emisivity measures the abilities of the object to radiate the red energy, which carries the information about the temperature of the given object. It can have value of 0 up to 1. Most of the surfaces has got the value of 0.95 and therefore most of the devices are set for this value. However some devices have the option to set the emisivity values.
Accuracy of the measuring
The accuracy of the manual infrared thermometer is determined by the ratio of the distance from the measured spot. The measured surface is getting bigger as the distance of the measuring is getting bigger. If the distance from the measured device is for example 1000mm (1m) and you are using the infrared thermometer with ration 12:1 then the maximum distance which can still provide reliable results is 83mm. The distance you can use for reliable results can be calculated by the formula D/S x target size. In this case D = 1000 and S = 12. Therefore 1000 / 12 = 83.
At the measuring it is necessary to keep in mind that the measured object must be larger than the measured spot, or at least the same size. But in case the measured spot is bigger then the object itself the values and the measuring itself will be incorrect.
recommended - the measured object is bigger than the measured area
acceptable - the measured object is of the same size as the measured area
unsuitable - the measured object is smaller than the measured area and measuring is affected by the temperature of the background