Measurement object

1. Material and emissivity.

A thermal imager measures the long-wave infrared radiation which is emitted by an object. The quantity of infrared radiation which is emitted (by the object itself), depends on the surface of the material.

Please note: Every surface has a specific emissivity.

2. Colour

The colour of the surface has no significant effect on the long-wave infrared radiation emitted by the measurement object. The crucial factor is the temperature. For example, a heating radiator painted black emits exactly the same amount of long-wave infrared radiation as a radiator which is equally warm, and painted white.

Please note: The colour of a surface hardly plays a part.

 

3. The surface of the measurement object

In thermography, the structure of the measurement object's surface plays a crucial role. For the emissivity of the surface varies according to the structure of the surface, soiling or coating.

Surface structure

As a rule, the emissivity of smooth, shiny, reflective and/or polished surfaces is somewhat lower than that of matt, structured, rough, weathered and/or scratched surfaces of the same materials.

Please note: When measuring smooth surfaces, pay particular attention to possible radiation sources in the surroundings (e.g. sun, heating etc.).

Moisture, snow and frost on the surface

Water, snow and frost have relatively high emissivities (approx. 0.85 < ε < 0.96), which is why the measurement of these substances is generally not a problem. However, you must bear in mind that the temperature of the measuring object can be distorted by natural coatings of this kind. Because moisture cools the surface of the measurement object when it evaporates, and snow has good insulating properties. Hoarfrost usually does not form a sealed surface, so the emissivity of the hoarfrost as well as that of the surface underneath it must be taken into account when measuring.

Please note: If possible, avoid measuring on wet, snow-covered or frost-covered surfaces.

Dirt and foreign bodies on the surface

Dirt and foreign bodies such as dust, soot or lubricants on the surface usually increase the emissivity of the surface. For this reason, measuring dirty objects is generally unproblematic. However, your thermal imager always measures the temperature of the surface, i.e. the dirt, and not the exact temperature of the surface of the measuring object underneath.

Please note: Avoid measuring on loose dirt (falsified temperature due to air inclusion).

Theoretical principles of thermography

Find out more in our compact tutorial on the physical principles of thermography. A real advantage, for example for setting the right emissivity for every surface.