Non-contact temperature measurement using infrared thermometers and thermal imaging cameras
Every object with a temperature above the absolute zero point of -273.15 °C (= 0 Kelvin) emits electromagnetic radiation proportional to its own temperature from its surface, the so-called intrinsic radiation. A part of this radiation is infrared radiation, which is used by IR temperature sensors and thermal imaging cameras for measuring the temperature. The infrared spectral range makes up only a very limited portion of the entire electromagnetic radiation spectrum. It ranges from the end of the visible spectral range at about 0.78 µm up to wavelengths of 1000 µm. For thermal imaging cameras and IR sensors, only the wavelength range from 0.7 to 14 µm is relevant. Above this wavelength the energy amounts are so small that detectors are not sensitive enough to measure them.
The infrared radiation penetrates the atmosphere and is focussed on a detector element in the infrared temperature sensor using a lens (input lens) which produces an electrical signal in proportion to the radiation. The signal is amplified and converted using downstream digital signal processsing into an output size proportional to the object temperature. The measured value may be indicated on a display or may be output via a variety of interfaces. This facilitates the integration of IR thermometers and thermal imaging cameras in feedback control systems of the process controller.
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