Taking a step back into time, the characteristics of human body infrared radiation were employed by the security industry and used as a base for the development of PIR (Passive Infrared Detector). Infrared waves radiate from the human body at 3~50μm, among them, 8~14μm occupies 46 percent, and the peak radiation is reflected around 9.5μm. Utilizing this infrared radiation characteristic, the human race is the steadiest infrared radiator as a homothermic being. An infrared thermography detector cannot emit any energy but passively receive and detect radiation from certain conditions. The detector will acclimate a few seconds after installation, and on-site infrared radiation will maintain the same state without any humans or animals entering into the detecting area. Once someone enters it, the optical system will focus on it and create mutative electrical signals via the pyro-electric transducer component, therefore triggering an alarm. The disadvantages of these kinds of products are obvious, a high rate of false alarms, which could easily be affected by thermal sources such as air-conditioners and heaters, the existence of detecting dead zones, indirect visualization, no confirmative circumstance after detecting and alarming, as well as having the need of on-site observation or cooperative use of visual monitors.
The visualized processed image emitted by an infrared detector is referred to as thermography. Radiating capacity of different objects, even different parts from the same object is diverse, as well as their reflection to radiation. Utilizing radiation differentiates objects from their environment, and also differentiates from each part of a scene. Thermography can present each scene as part of radiating fluctuation to display the thermal energy distribution of the scenario. It is like a third human eye being able to visualize the imperceptible world beyond human recognition.
Using a camera of infrared thermography makes of an optical imaging lens. The infrared detector will then receive the infrared energy emitted from the target, which transforms the energy into an electrical signal via the detector. Criterion visible infrared thermography can be transformed after enlargement and image algorithm processing. This thermography corresponds with the thermal distribution field of object surfaces; it is a thermal distribution graph of each part of infrared radiation from the target object.
Critical components and infrared thermal imaging camera technology include: infrared focal plane detectors, image processing algorithms, electrical processing circuits, thermal imagery lenses, production adjusting technology and detection, and thermometry algorithms.
As core component detectors include cooled and non-cooled, it is mainly applied for commercial utilization. Detector technology has been developing for decades, it was typically applied in the military field for a long time. In the late 80s, focal plane arrays (FPA) with gaze-type area array technology appeared and developed, which accelerated the application of thermal imaging technology in the commercial field.
Detector units (pixels) utilize temperature sensitive micro-bolometers of thermistor material or pyro-electric crystalline materials on the basis of pyro-electric effects are closely laid on the focal plane of FPA. At present, materials including polycrystalline silicon, vanadic acid anhydride, ferroelectric film, etc. are frequently used. Each FPA pixel can detect the smallest unit of infrared energy, and each pixel is an independent thermometry point. The more pixels that are detected that includes thermometry points equals imaging effects. Major pixels of thermal imagery detector are: 60×60/80×80/120×12 0/140×140/180×180/160×120/240×180/320×240/384×288/420×315/64 0×480, etc., liketotal amount of pixels of 420×315 is 132,300 (420 pixels×315 pixels=132,300 total pixels). Detectors with low pixel numbers are mainly used for short distance detection of handheld devices, and detectors with medium and high pixel numbers are mainly used for image observation and medium and long distance detection.
Image processing algorithms and electrical processing circuits are critical technologies of productization. Infrared radiating energy received by detectors are transformed into electrical signals by electrical processing circuits, the signal is inputted to read out circuits after enlargement processing, then transfer Analog to Digital (A/D) and send it into processing chips of videos and images to algorithms that will process it and do video composition. The infrared signals irradiating from objects that are detected are extremely weak and lack gradation of stereo visible light images, thus a series of algorithms process things like image brightness, contrast, uniformity, visualized false colors and others that are used for these requirements. In this process, circuit design is particularly important. Besides solving electronic noise and disturbances, specific attention should be paid to thermal noise influences, and good denoising features that will contribute to better product performance. Image algorithms include: non-uniformity revising, defective pixel replacement, automatic dimming, image enhancement, thermometry, false-color coding, infrared thermometry analysis in real time, image compression, code processing, and others, and then eventually receive continuous thermal images.
Product adjusting technology and detection are core technologies for each supplier, and public information about these technologies are quite rare. Depending on self-established product adjustments and detecting procedures, Sunell efficiently distinguishes between each single detector and guarantees uniformity of delivered products.
Instinctive and unique characteristics of infrared thermal imaging cameras determine its qualitative features, detecting and finding targets to recognize active humans or animals instead of quantitative detail identification. It includes the three foll owing merits compared with traditional visible light cameras:
I. Available For any Light Environment
Traditional camera shoots rely on natural or light environments, but infrared thermal imaging cameras can gather images clearly from infrared thermal energy radiating from objects without any other light. Infrared thermal imaging cameras are available for any light environment without being influenced by bright light. It can clearly detect and find targets in the day and recognize disguised and covert targets. Thus it can actually perform 24 hour monitoring during day and night.
II. Monitor Distributing Temperature
Fields of Target Thermal Energies Infrared thermal imaging cameras can display the field temperature of objects and turn the invisible temperature distribution of object surfaces into visible thermal images. Through monitoring temperature fields, abnormal temperatures can be detected immediately to prevent hidden dangers, like fire disasters. Meanwhile, these received thermal temperature fields will not likely be influenced by diverse uncommon light (like glare, stray lights and others) because for visible light cameras, relative images are simpler and more suitable for some image processing intelligent analysis software.
III. Capable of Real Cloud and Mist Penetrability
Light and near infrared rays will beinfluenced from atmospheric factors such as, clouds, mist, smoke and dust, but for thermal infrared from 3~5 micron meters (medium wave infrared channel) and 8~14 micron meters (long wave infrared channel) these factors are transparent. Therefore, traditional cameras can hardly shoot a clear image in cloudy and misty conditions, but thermal imaging cameras can accomplish it efficiently.
In conclusion, infrared thermal imaging cameras can collect, process, and visualize images of infrared thermal radiating phenomena which are invisible, untouchable, and extensively exist in nature, and ultimately delivers us a more visible thermal world, just as a third eye provides vision to the world.
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