Sensoriamento de temperatura infravermelho - Termografia
Non-contact temperature measurement is an optical measurement based on the property of all materials to send out electromagnetic radiation (infrared radiation). The infrared measuring instrument (pyrometer or thermal imager) uses this radiation to determine the temperature.
Thermal imagers operate in the short, mid, and long wavelength. To choose the correct measuring instrument for a certain application different properties of the measuring object have to be taken into consideration, such as temperature, wavelength, material, and surface.
Energy travels throughout the universe at the speed of light in the form of electromagnetic radiation. Depending upon the energy level these radiations are classified as Gamma rays, X rays, ultra violet rays, visible rays, infrared rays, micro waves and radio waves. Together all these types of radiation make up one long continuous spectrum called “Electromagnetic spectrum”
Energy level of the electromagnetic radiation is measured in terms of wavelength denoted by (λ). Sometimes segments of electromagnetic spectrum are described in terms of frequency (f). The relationship between wavelength and frequency is
f = 1/ λ
Energy levels between 0.75 µm to 14 µm on the electromagnetic spectrum is infrared radiation. All objects above 0 °K emit radiation (energy) from their surface in the form of electromagnetic waves due to vibration of atoms. The amount of energy emitted depends upon surface temperature and surface characteristics.
The Temperature Range:
Our thermal imagers measure temperatures from -40 to 3000 °C. The instruments are available in different temperature ranges. The selection of the temperature range depends on the application.
Emissivity is highly dependent on the material and its composition. In order to measure the temperature of the target object accurately, one will need to know:
- type of material used in the target object (e.g. cast iron, aluminum, steel etc.)
- material composition (e.g. Alloy 20 NI, 24 Cr, 55 Fe or Brass 73% Cr, 27% Zn etc.)
In addition to the material and material composition, knowing the surface condition of the target object is also very important. The surface condition may be:
- Smooth or rough surface
- Dark or Light color
- Oxidized or non-oxidized
- Polished or dull
- Rusted or coated or painted
- Porous or impermeable
- Galvanized or not
Knowing the surface condition and taking into consideration while determining emissivity will reduce uncertainty in the measurements.
A table with emissivities of various materials can be downloaded. (314 KB)
Emissivity of a material can change depending on the wavelength. This is especially true for metals. The ability of a metal to emit thermal radiation increases at shorter wavelengths. Therefore for metal applications, it is best to select a thermometer which measures short wavelength. Transparent objects such as glass, plastic films or gases have a distinct wavelength ranges in which the radiation characteristics are good. In order to accurately measure the temperature of these objects, it is necessary to select radiation thermometers with special sensor and filters which are sensitive to a particular wavelength.
|Plastic films made of PE, PP, PS||
Plastic films made of PET, PA , PUR
Cold flue gases
Hot flue gases