Infrared Thermography is the technique that uses an infrared imaging and measurement camera to “see” and “measure” invisible infrared energy being emitted from an object.
Thermal, or infrared energy, is energy is not visible because its wavelength is too long for the sensors in our eyes to detect at temperatures below 525 degree Celsius. It is the part of the electromagnetic spectrum that we perceive as heat. Unlike visible light, in the infrared spectrum everything with a temperature above absolute zero emits infrared electromagnetic energy. Even cold objects such as ice cubes emit infrared radiation. The higher the temperature of the object, the greater the infrared radiation emitted. The Infrared camera converts the radiation into an electrical output to form a two dimensional image and allows us to see levels of energy that our eyes cannot discern!
In the industrial/commercial environment, almost everything gets hotter or cooler before it fails, making infrared cameras extremely valuable diagnostic tools with many diverse applications. As industry strives to improve manufacturing efficiencies, manage energy, improve product quality, and enhance worker safety, new applications for infrared cameras continually emerge.
Energy loss, especially form structure, has been highlighted in the latest building codes and faulty refractory or insulation in industry adds to the outlay for energy, increasing consumption and raising the cost of products. There is no better inspection techniques that Infrared Thermography to find these thermal anomalies.
Thermography is used in so many industries for such a variety of application, it is no wonder that most companies have looked into using this technology in some form. The list of applications is limited by imagination but include:
HOW DOES AN INFRARED CAMERA WORK?
All objects, cold or hot, radiate energy in the form of electromagnetic radiation or infrared radiation which is basically photons of light but in a wavelength that we cannot perceive in the visible spectrum unless the temperature is above 525 degrees Celsius.. As an object increases in temperature, it radiates more energy and the peak emitted energy mover towards shorter wavelengths. Infrared radiation, visible light and ultraviolet light are all forms of energy in the electromagnetic spectrum. The only difference is their wavelength or the frequency of the wavelength.
The human eye can only see a narrow range of wavelength in the electromagnetic spectrum. These wavelengths range in length from 0.4 to 0.7 microns, a micron is one millionth of a metre. Most of what the eye sees is reflections from objects that high energy from the sun or an incandescent light bulb is striking. If the temperature of an object gets hot enough however, above 525°C the energy from that object will radiate a small amount of energy in the visible spectrum and we will see it, like the incandescent glow from a tungsten light bulb. This is when we see an object like the element on an electric stove “glowing” red. Mostly, however we see reflected light.
The infrared camera can detect infrared energy well before we can see it with our eyes. Most cameras can image temperatures from -20 to 500°C and can be extended down to -40°C and up to 2000°C. The camera converts this invisible infrared energy into a two-dimensional visual image and displays this on a standard TV monitor. Most industrial cameras can also make temperature measurements, with accuracies to around ±2% at 30°C. The thermal information is stored onto a disc and is later downloaded into a computer to create report.
Modern industrial infrared cameras use special materials that record the level of radiation emitted from the surface of an object, the camera The energy passes through the camera optics (These are typically man grown crystals that have a high transmission rate for specific wavelengths, Germanium is often used. The optics focus the radiation onto the detector pixels, similar to a magnifying glass in the visible spectrum, and the detector converts the radiation into an electrical output from each detector pixel. Today’s cameras are known as Focal Plane Array cameras with thousands of detector pixels – a common detector resolution is 320 x 240 which equals 76,800 detector pixels. The electronic output is displayed as a two dimensional image usually on an LCD viewing screen although some cameras also have a viewfinder. The presented image is called a ‘Thermogram’ and it displays the energy levels as either Black & White or false colour which to our eyes appear as a two dimensional image.
INFRARED INSPECTIONS ARE SIMPLE
However, taking thermal images and gathering thermal information is quite easy these days, just push the auto button and there is an image! This is simple on the surface, but it is not as easy as it sounds. The real work — and value — is what the Thermographer understands about the object of interest, how it operates, the heat transfer within and to the surface of the object, how to adjust the camera to enhance the thermal details necessary to evaluate the image once it is stored and downloaded onto the computer. Then prepare a report that is accurate, clearly presented and is easy to read by the maintenance personnel, who generally do not know anything about Infrared Thermography. As in any method of non-destructive testing, the interpretation of the information gathered takes both education and experience.
This is NOT a “point and shoot” technique, as most camera manufacturers would like you to believe!
An access cover on a vessel. The bolted area displays a much higher energy level than the rest of the cover. This is an example of the ability of materials to emit different levels of radiation. To understand this situation and be able to handle it for temperature measurements is fundamental to using infrared thermography cameras.
INFRARED TRAINING AND EDUCATION
The above outlines the reasons why a training course by field experienced trainers is vital to any person doing field inspections. The courses teach people how to fully utilise the infrared camera and software, to gather accurate meaningful data, and, to be able to correctly interpret the information and present the information in a clear understandable format.
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