What is emissivity?

Pyrometers or infrared temperature sensors are sensors for easy, safe, fast and non-contact temperature measurement of objects and surfaces in industrial processes. However, in order to measure temperature accurately, it is necessary to know the emissivity of the surface that has to be measured.

Emitted, reflected and transmitted energy

All surfaces emit infrared radiation. The amount of energy emitted depends on the temperature and emissivity of the material. To accurately measure the temperature of a surface, the infrared sensor must know how much of the energy comes from the material itself, and how much of the energy comes from reflected energy or transmitted energy. The emissivity of a surface is a measure of how effectively a surface emits infrared radiation. The emissivity setting of the sensor should match the emissivity of the target surface for maximum accuracy. In our sensors it is possible to adjust to this with an emissivity correction setting.

The sensor detects infrared radiation of three possible sources.
In order to measure the temperature accurately, it is necessary to know how much of the
detected energy was emitted by the target itself (target object)

Materials with a high emissivity

E.g. painted or very dirty surfaces, food, rubber, thick plastics, paper, glue and asphalt

The emissivity of these materials is often close to 0.95. This is the standard emissivity setting of all i-Tec sensors. A surface with a high emissivity is easy to measure, so standard (cheaper) sensors can be used for this. The amount of reflections on these materials are minimal.

High emissivity materials can be easily measured up to temperatures of 1000°C with standard sensors from 8 to 14 μm, such as the i-Tec E series, PyroSigma
and i-Tec Mini provide good results.
It is also possible to use a short wavelength sensor if the surface temperature to be measured is very high. A suited option is the i-Tec USB. Note: the color of a surface usually has very little influence on the emissivity.

Materials with low emissivity

**E.g. clean, bare and reflective metal surfaces including iron and steel**

Reflective surfaces have a low emissivity which makes it more difficult to measure accurately. If the emissivity of the material and the surface are known, then it is possible to perform a good measurement on, for example, bare metal using a special i-Tec with a shorter wavelength.

When it is possible to treat the surface of reflective materials so that it no longer reflects, it could be an interesting way to enable the use of the more affordable 8 to 14 μm sensors. If this is not possible, it is recommended to try a sensor with a short wavelength, such as the i-Tec USB
or i-Tec Mini 2.2.
Some metals, often aluminium and copper, are very challenging to measure.
Please contact our experts for this.

Materials that transmit (all) energy

**E.g. thin plastic films or transparent films and silicon**

Most transparent materials transmit all infrared wavelengths required for a temperature measurement. This makes it very difficult to measure the temperature of these materials consistently.

If the material has a thickness of approx. 1-2 mm, there is a possibility to measure the product with, for example, the i-Tec CUBE P. Ask our experts for advice!