What is emissivity?

You have all probably already used an infrared thermometer? Have you ever wondered if your infrared thermometer is accurate? Yes, but only if your emissivity is well adjusted!

Emissivity is an important concept in temperature measurement. It defines the capacity of a material to emit heat in the form of infrared. Measuring the temperature of an object is done by measuring the quantity energy issued in the form infrared. This is why it is a key factor in getting an accurate temperature reading. To understand this, experts from thermometre.fr answer you.

How to better understand emissivity? 

Emissivity is the capacity of a body or surface to absorber and to emit energy radiated. In other words, the higher the emissivity weak (close to 0), the more material is insulating in terms of radiation and more transfer energy is then reduced. THE black materials, which absorb the light, tend to have a higher emissivity high. THE materials clear, such as the metal, have a 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 denoted "e". This coefficient makes it possible to measure the quantity energy absorbed and emitted by a material, and varies in function from wave length. 

The emissivity coefficient is also influenced by three factors: 

• The nature of the material concerned
• Surface condition of the material (smooth, rough, colored, etc.)
• The material temperature

What is the emissivity released by materials and foodstuffs? 

Objects having a high emissivity are mainly the materials non-metallic And non-opaque, such as glass (0.92), plastic (0.84 to 0.94), plexiglass (0.86), quartz or vitreous china (0.92), as well as tile (0 .97), polypropylene, plaster (0.86), rubber (0.95), brick (0.94) and paint. 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 (0.16 to 0.70), silver (0.03), copper (between 0.006 and 0.88), zinc (from 0.04 to 0.20) or even lead (0.28), have a weak emissivity.

Most of substances organic have an emissivity between 0.95 and 0.97. This value is therefore stored fixedly in many devices to avoid measurement errors caused by incorrectly 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 taking the temperature of an aluminum plate heated to 100°C: 

As you can see, a poorly informed emissivity distorts temperature measurement results. As you can see from the table below, the emissivity of aluminum is 0.10. 

The infrared thermometer

When using infrared thermometers, it is important to understand the emissivity of the material you are measuring. If emissivity East poorly defined, the temperature reading can be distorted. For example, if you measure the temperature of a metal object with an emissivity set for a black surface, you will get a much lower reading than the actual temperature. 

	RayTemp 3	RayTemp 8
Temperature range	-60°C to +500°C	-60°C to +500°C
Type K probe socket	Non	Yes
Temperature range with probe	/	-64°C to +1370°C
Resolution	+0.1°C	+0.1°C
Accuracy	+/-0.2°C	+/-0.2°C
Field of view	12:1	12:1
Adjustable emissivity	No (Fixed at 0.97)	Yes
Autonomy	140 hours	180 hours
Display	LCD	LCD
Guarantee	1 an	1 an
Measuring scale	Degree Celsius and Fahrenheit	Degree Celsius and Fahrenheit

Fortunately, most modern infrared thermometers are equipped with a function emissivity adjustable. This allows you to set it based on the area you are measuring. However, it is always important to research the area you are measuring to determine emissivity appropriate.