Tuesday, January 24, 2012

Active Thermography and its Application

Thermography or thermal imaging is a type of infrared imaging. Thermal imaging camera sensors detect heat in the infrared range of the electromagnetic spectrum (roughly 900–14,000 nanometers or 0.9–14 ┬Ám) and produce color or black and white images from heat signatures. It is widely used in manufacture and industry to do preventive maintenance for the machinery. One of the strengths of the technology is that it is non-contact, meaning inspection can take place even on live systems where there may normally be dangerous temperatures, electrical currents or high speed moving parts. So from a safety point of view it has some real benefits.

Thermography enables systems to be inspected under real operating conditions. So mission critical or high value processes such as manufacturing can continue during the thermal inspection. In high value processes the cost of maintenance can be greatly reduced by predicting when repairs or routine maintenance are needed. This enables maintenance to be planned, which in turn can minimize costly down time. Mechanical wear and tear cannot always be detected until there is a catastrophic failure. For example, if a worn bearing is put under load it gets hot, which can be detected with a thermal imaging camera.

Those two benefits: cost reduction and ease of maintenance make it powerfull tool for preventive maintenance. The following two pictures are example of thermal imaging for detection of mechanical condition and water leak detection in pipe. The high temperature shows the condition of captured device, if it is higher than boundary condition, it can be categorized as abnormal or defect area.

Example of themal imaging [1,2]

Active themography
Active thermography is imaging techniques based on the evaluation of a previously excited heat flow in the tested component and its disturbance by hidden defects. The heat flow is generated with a heat pulse or through sinusoidal modulation. Testing is carried out with an IR-camera, followed by a mathematical analysis of the measured sequence to extract the information necessary for reliable defect detection. The applications of thermographic methods to measure defects (or porosity) quantitatively and to assess parts with a complex 3D-structure still hold unsolved problems. Induction thermography is a special kind of active thermography for the characterisation of metals. In induction thermography the excitation is done by means of a HF-field and eddy currents are subsequently induced. Since eddy currents are influenced by the presence of cracks, the latter can in principle be detected thermographically.

Active Thermography for Quantitative NDT of CFRP Components 
This application presents a calibration-free approach to determine thicknesses and interface parameters out of at least two lock-in measurements at different modulation frequencies. The separation between properties of the layer and the interface beneath is particularly important for the characterization of adhesive joints CRFP (Carbon fiber-reinforced plastics) components.

General setup of active thermography
Example of Active heat flow thermography that allows testing of modern composite materials and lightweight construction elements in cockpit.

Insulation failure in the cockpit [4]

Source:
  1. http://www.waterleakdetectionuk.co.uk/water-leak-detection-thermal-imaging/
  2. http://www.waterleakdetectionuk.co.uk/water-leak-detection-thermal-imaging/
  3. http://flirindonesia.co.id/v2/index.php/sidebar/item/11-security-systems
  4. http://www.infratec.eu/thermography/application-area/process-optimisation/aviation.html
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