Measurement surroundings

1. Ambient temperature.

You should also factor in the setting of the reflected temperature (RTC) as well as the emissivity setting (ε) so that your thermal imager can calculate the surface temperature correctly.

  • In many measurement applications, the reflected temperature corresponds to the ambient temperature.
  • Ensuring the emissivity setting is exactly correct is important where there is a large difference in temperature between the measuring object and the measuring environment.

2. Radiation and interference sources

Every object with a temperature above absolute zero (0 Kelvin = 273.15 °C) emits infrared radiation. Objects with a large difference in temperature from the measuring object can disrupt the infrared measurement as a result of their own radiation. You should avoid or deactivate sources of interference of this kind wherever possible.

  • Shield the sources of interference, e.g. with a screen or a cardboard box.
  • You can measure the reflected radiation, for example using a Lambert radiator in combination with your thermal imager.

3. Weather

Clouds

Carry out outdoor infrared measurements ideally under densely cloudy skies. The reason: The measurement object is shielded from solar irradiation and "cold sky radiation".

Precipitation

Water, ice and snow have high emissivity and are impervious to infrared radiation. In addition, the measurement of wet objects can result in measurement errors, as the surface of the measuring object cools down as the precipitation evaporates.

Please Note: Heavy precipitation (rain, snow) can distort the measurement result. 

4. Air / Air humidity

If the lens (or the protective glass) of the thermal imager has condensation from a high relative humidity, the infrared radiation cannot be fully received. Due to the water, the radiation does not completely reach the infrared imager's lens. Extremely dense mist can also affect the measurement, as the water droplets in the transmission path let less infrared radiation through.

Please note: Ensure that the relative air humidity in the measurement surroundings is low. This allows you to avoid condensation in the air (fog), on the measurement object, the protective glass or the thermal imager's lens.

Air flows

As a result of the heat exchange (convection), the air close to the surface is the same temperature as the measuring object. If it is windy or there is a draught, this layer of air is “blown away” and replaced by a new layer of air that has not yet adapted to the temperature of the measuring object. As a result of convection, heat is taken away from the warm measuring object or absorbed by the cold measuring object until the temperatures of the air and the surface of the measuring object have adjusted to each other. This effect of the heat exchange increases the greater the temperature difference between the surface of the measuring object and the ambient temperature.

Please note: Wind or a draught in the room can affect the temperature measurement with the thermal imager.

Air contamination

Some suspended particles such as dust, soot and smoke, for example, as well as some vapours have high emissivity and are barely transmissive. This means that they can impair the measurement, as they emit their own infrared radiation that is received by the thermal imager. In addition, only some of the infrared radiation of the measuring object can penetrate through to the thermal imager, as it is scattered and absorbed by the suspended matter.

5. Light

Light or illumination do not have a significant impact on measurement with a thermal imager. You can also take measurements in the dark, as the thermal imager measures long-wave infrared radiation. However, some light sources emit infrared thermal radiation themselves and can thus affect the temperature of objects in their vicinity.

  • Therefore do not measure in direct sunlight or near a hot light bulb, for example.
  • Cold light sources, such as LEDs or neon lamps, are non-critical: They transform the major portion of the energy used into visible light, and not into infrared radiation.

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.