Interpretation is king

Published:  05 March, 2010

Interpretation is king

There is no doubt that thermal imaging is now a fantastic tool for detecting electrical faults but the infrared cameras used today bear no similarity to those employed even 10 years ago.  PWE reports.

 It's hard to believe that not so long ago a transit van was needed to accommodate all the kit necessary to conduct a thermal survey.  Today"s infrared camera is easily portable and year on year the technology is being developed to provide better image quality and the necessary software tools to make the job easier, quicker and more efficient.

The world’s first portable thermal imaging camera with 640 x 480 detector is now commercially available outside the scientific community providing unrivalled image quality.  To put this into perspective, this gives more than 307,000 pixels or measurement points whereas the nearest alternative provides just 76,000.  This means the image quality is far superior and that the camera can be used at greater distances away from the target, an important development in the inspection of high voltage installations.

No longer the sole preserve of the professional thermographer thermal imaging is now widely used by a range of trades. Infrared cameras now fall into two basic categories beyond those designed for professional and in-depth thermal analysis.  Next in line are the models aimed at those conducting regular condition monitoring surveys with a need for good image quality, data collection plus analysis and reporting, but not for the sophisticated features of the high-end cameras.

Typically they will offer a middle range detector - 160 x 120 or 320 x 240 – operate with a frame rate of 50Hz, have a choice of optics and possibly composite video output and digital zoom.

The infrared cameras that are really extending the use of thermal imaging in general electrical inspection sector are the new generation of find-it-fix-it models.  These easily portable, torch-style cameras are true toolbox tools designed for spot checks and limited analysis.  They have become a viable option thanks to developments in detector technology that has allowed the purchase price of the camera to be set at a level that within the scope of any professional electrician.

All thermal imaging cameras have the common benefit of allowing thermal irregularities to be spotted in an instant. However as professional thermographer Stuart Burrows, points out: "There are a lot of things out there to mislead and even if you are just fault-finding rather than conducting critical thermal analysis there are things you need to know. Interpretation is king.” Burrows has used thermographic techniques in many applications with the predictive maintenance specialists ETEK Limited based in Bury, Lancashire.

Reflections from overhead lighting and the paint chosen to finish a cabinet can both have a profound effect on results.  “A cabinet may be glowing hot in the thermal image but its shiny surface could just be the heat from a light,” Stuart advises. “If you suspect this, move your viewpoint to eliminate the reflection.  You must also watch out for the emissivity values of paint. For example, Finch Aluminium has a value of .23 and GSFC White, .92.  One way to avoid this problem is to stick high-emissivity electricians tape onto the target or make a note of the paint used so that you can apply the emissivity value after the survey.”

The electrician also needs to put the problem into context.  For example, is there a high current or high resistance contact where a higher operating temperature may be the norm?  A sound knowledge of cable ratings is also of course essential.  “What may be a safe temperature for LSF covered cable, will not be for general PVC covered cables which should not exceed 70°C and will give off highly toxic fumes when burned.

As Burrows concludes: “It can often be difficult in the field to determine what is a problem and what isn’t.  My rule of thumb is if it’s hotter than me, flag it!  You can always eliminate it as a problem at a later stage.”

Taking a course in basic thermography is undoubtedly the best action plan for any electrician seeking to adopt this technology.  It will provide a basic grounding in the principles of infrared and include a practical workshop that covers elementary interpretation of the thermal images.

With thermography so readily available there is unfortunately a trend towards underplaying the need for training but it is vitally important to ensure infrared cameras are used to best effect.  A good infrared manufacture will of course provide such rudimentary training as part of the camera package but beyond that there is a range of certification courses available in the UK.

Accredited by the British Institute of Non-Destructive Testing there are three certification levels now available.  For an electrician simply conducting a survey, Level I is a good option but if that survey is to include analysis Level II is appropriate.  Level III is aimed at those whose work involves creating and imposing thermal benchmarks and standards.

In summary, thermal imaging can be a real boon to those involved in electrical inspection but don’t just buy a camera and stop there.  Dedicated training provides the knowledge for the operator to interpret the results more effectively and to spot more faults before they become expensive failures.

 

For further information please visit: www.flir.uk.com

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