What is emissivity?

Have you all already used an infrared thermometer? Have you ever wondered if your infrared thermometer was precise? Yes, but only if your emissivity is well settled!

Emissivity is an important concept to temperature. It defines the capacity of a material to issue heat in the form of infrared. The measurement of the temperature of an object is done by measuring the quantity energy emitted in form infrared. This is why it is a key factor to obtain a precise temperature reading. To understand this, the experts of Thermometre.fr answer you.

How to better know emissivity? 

Emissivity is the capacity of a body or surface to absorb and at put forward energy radiated. In other words, the more emissivity is weak (close to 0), plus the material is insulating in terms of influence and the more the transfer energy is then reduced. THE black materials, which absorb the light, tend to have more emissivity high. THE materials clear, such as the metal, have lower emissivity. 

What is the emissivity coefficient?

In order to fully understand this concept, it is important to know in detail the coefficient emissivity. Without unit, this coefficient is included Between 0 and 1 And is noted "E". This coefficient makes it possible to measure the quantity absorbed energy and issued by a material, and varies in function of the wavelength. 

The emissivity coefficient is also influenced by three factors: 

• There material nature concerned
• Surface state material (smooth, rough, colorful, etc ...)
• There material temperature

What is the emissivity released by materials and foodstuffs? 

Objects with a high emissivity are mainly materials non -metallic And non -opaque, such as glass (0.92), plastic (from 0.84 to 0.94), Plexiglas (0.86), quartz or vitrified porcelain (0.92), as well as the tile (0 , 97), polypropylene, plaster (0.86), rubber (0.95), brick (0.94) and painting. They are therefore those who re -emit a large part of infrared radiation that they receive.

On the other hand, the materials reflective, such as aluminum (generally less than 0.10), steel (from 0.16 to 0.70), silver (0.03), copper (between 0.006 and 0.88), the zinc (from 0.04 to 0.20) or lead (0.28), have a weak emissivity.

Most substances organic have emissivity between 0.95 and 0.97. This is why this value is fixed fixed in many devices to avoid measurement errors caused by poorly adjusted emissivities.  If the emissivity is unknown, it can be determined with the thermometers infrared which offer the possibility of connecting an external contact temperature probe.

Here is the example of the temperature intake of an aluminum plate heated to 100 ° C: 

As you can see, a Poorly enforced emissivity false temperature measurement results. As you can see on the table below, the emissivity of aluminum is 0.10. 

The infrared thermometer

Using infrared thermometers, it is important to understand the emissivity of the material you measure. If emissivity East ill -defined, reading the temperature can be distorted. For example, if you measure the temperature of a metal object with a defined emissivity for a black surface, you will get a much lower reading than the actual temperature. 

	Raytemp 3	Raytemp 8
Temperature range	-60 ° C at +500 ° C	-60 ° C at +500 ° C
Type K type taking	No	Yes
Temperature range with probe	/	-64 ° C to +1370 ° C
Resolution	+0.1 ° C	+0.1 ° C
Precision	+/- 0.2 ° C	+/- 0.2 ° C
Field of vision	12:1	12:1
Adjustable emissivity	No (fixed at 0.97)	Yes
Autonomy	140 hours	180 hours
Display	LCD	LCD
Guarantee	1 year	1 year
Measurement	Degree Celsius and Fahrenheit	Degree Celsius and Fahrenheit

Fortunately, most modern infrared thermometers are equipped with a function emissivity adjustable. This allows you to define it according to the surface you measure. However, it is always important to do research on the surface that you measure to determine emissivity appropriate.