Infrared (IR) energy is part of the electromagnetic spectrum and behaves similarly to visible light. It travels through space at the speed of light and can be reflected, refracted, absorbed, and emitted. IR energy has a wavelength longer than that of visible light, typically between 0.7 and 1000 micrometers (millionths of a meter). Infrared is usually divided into 3 spectral regions: near, mid and far-infrared.
Sir William Herschel first discovered the Infrared spectrum, back in 1800. By 1917, Infrared was being utilized on the Battlefield by the British. In the 1950’s thermal images were being produced. In 1952, the heat seeking Sidewinder missile was created. In 1965, the technology became commercially available. Since that time, there have been numerous advancements in not only the equipment, but also a better understanding of its uses.
All objects above absolute zero (-273.16°C, -459.67°F) emit infrared radiation as a function of their temperature. This means all objects emit infrared radiation. Infrared energy is generated by the vibration and rotation of atoms and molecules. The higher the temperature of an object, the more the motion and hence the more infrared energy is emitted. This is the energy detected by infrared cameras. Infrared cameras do not measure temperature directly. They measure the thermal radiant energy coming from an object. For opaque objects, this depends on several factors: object temperature, emissivity, reflectivity, and reflected apparent temperature.
Infrared Thermography is the technique of producing an image of invisible (to our eyes) infrared light emitted by objects due to thermal conditions. The most typical type of thermography camera resembles a typical camcorder and produces a live TV picture of radiation. More sophisticated cameras can actually measure the temperatures of any object or surface in the image and produce false color images which make interpretation of thermal patterns easier. Images produced by an infrared camera are called thermograms or sometimes a thermograph.
Emissivity is defined as the ratio of the energy radiated from a material's surface to that radiated from a blackbody (a perfect emitter) at the same temperature and wavelength and under the same viewing conditions. It is a dimensionless number between 0 (for a perfect reflector) and 1 (for a perfect emitter). The emissivity of a surface depends not only on the material but also on the nature of the surface. For example, a clean and polished metal surface will have a low emissivity, whereas a roughened and oxidized metal surface will have a high emissivity. The emissivity also depends on the temperature of the surface as well as wavelength and angle.
The IR camera captures the radiosity of the target it is viewing. Radiosity is defined as the infrared energy coming from a target modulated by the intervening atmosphere, and consists of emitted, reflected and sometimes transmitted IR energy. An opaque target has a transmittance of zero. The colors on an IR image vary due to variations in radiosity. The radiosity of an opaque target can vary due to the target temperature, target emissivity and reflected radiant energy variations.
The term temperature anomaly means a departure from a reference value or long-term average. In terms of thermography, it is when the thermal gradient of the surface temperature deviates from the normal uniform thermal pattern that should exist for that particular component. A positive anomaly indicates that the observed temperature was warmer than the reference value, while a negative anomaly indicates that the observed temperature was cooler than the reference value.
The use of infrared thermography makes economic sense, regardless of the size and operation of your facility. Over the years it has consistently shown unprecedented returns on investment. According to The Hartford Steam Boiler Inspection and Insurance Company, for every dollar spent on infrared service there is a $5 return on investment for materials and labor from fixing the problem before it fails.
Thermal infrared imagers are detector and lens combinations that give a visual representation of infrared energy emitted by objects. Thermal infrared images let you see heat and how it is distributed. A thermal infrared camera detects infrared energy and converts it into an electronic signal, which is then processed to produce a thermal image on a video monitor and perform temperature calculations. Heat sensed by an infrared camera can be very precisely quantified, or measured, allowing you to not only monitor thermal performance, but also identify and evaluate the relative severity of heat-related problems. Thermal imaging cameras have lenses, just like visible light cameras. But in this case the lens focuses waves from infrared energy onto an infrared sensor array. Thousands of sensors on the array convert the infrared energy into electrical signals, which are then converted into an image.
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