Emissivity coefficient for thermal imaging cameras

The correct setting of the emissivity coefficient in a thermal imaging camera is essential in order to measure the correct temperature.

It must be done manually and match the test object. It can be fine-tuned for most models between 0 and 1.

The emissivity coefficient describes how much heat is emitted by an object compared to a black body. A black body is an idealized concept of a material that can absorb and emit heat radiation perfectly. The black body has an emission coefficient of 1 – that is, maximally high. However, real materials and objects are always above 0 and below 1.

A body with a higher emission level thus releases its heat faster. Each object to be tested for its temperature consists of a material and has an associated emissivity coefficient.

Some emissivity coefficients of common materials are:

 

Material Emissivity coefficient
Iron, blank 0,24
Glas 0,91
Paper 0,9
Human skin 0,97

Source: Wikipedia

 
 

The emissivity coefficients can be taken from tables. They are often found in the supplied operating instructions of thermal imaging cameras.

emissionskoeffizient physik

Emissivity coefficient and impact on the thermal image

An incorrectly adjusted emission level has no effect on the representation of the thermal image per se. However, thermal imaging cameras always display the temperature of a measuring point in the thermal image, and a conversion based on the emissivity coefficient is performed. Likewise, the thermal imaging camera must be regularly calibrated correctly so that the incoming heat radiation can be correctly recorded and a temperature can be calculated.

For a qualitative evaluation of the thermal image, the degree of emission plays no role when only temperature differences are used.

When buying a camera, care must be taken to ensure that the emissivity coefficient can be adjusted by 0.01 steps. In addition, this setting should be quickly and easily accessible, since one often has to deal with different materials.

If the thermal imaging camera has a function that calculates the average temperature of a surface, it is particularly important that only materials with the same emission coefficients are located in the measurement area. The same applies to the detection of the minimum and maximum temperature in these so-called measurement boxes.