Window of opportunity

Published:  06 November, 2015

If you want to conduct a live thermal inspection of electrical equipment the most effective and certainly safest way is via an infrared window. It’s a data collection point which is IR transmissible that allows meaningful data to be obtained without the thermographer encountering the dangers of arc flash. Martin Robinson, CEO – IRISS Inc reports.

Not only do infrared windows ensure a best practice approach to preventive maintenance and condition monitoring, however. They also allow electrical systems, previously considered to be too much of a safety hazard, to be brought into routine maintenance. For many companies, this is invaluable as these systems are often critical to the process or operation.

A very common question is: Can any brand of thermal imaging camera be used with any type of window? Naturally the infrared camera manufacturers will recommend their own brand of window. But, when armed with the necessary information, companies can make their own decision on the best combination for their business.

Quick guide

• Step 1: determine the type of camera to be used. Infrared detectors broadly fall into the wavelength of 1 – 12 microns. Shortwave covers 1 – 3 microns, medium wave 3 – 5 microns and longwave 8 – 12 microns. Longwave, uncooled cameras are the standard choice for maintenance and condition monitoring applications.

• Step 2: determine the type of material of the window being considered. The most common used for industrial thermography are calcium and barium fluoride, sapphire and IR transmissible polymer. Next consider the transmission range of those materials. Respectively they are .13 to 10 microns, .17 to 5.5 microns and 3 to about 12.5 microns.

• So when you correlate the data from both steps you can see the longwave cameras can’t be used with a sapphire window as the transmission ranges don’t tie up. This means you are left with a choice between a fluoride or polymer based infrared window systems. Both have the correct credentials on paper but which is the most suitable for industrial maintenance applications?

Think, harsh environment

Calcium and barium fluoride are crystals which by their very nature, are fragile. There are certainly applications that are well served by this type of window, particularly in the lab, but they are not the best choice for harsh industrial or uncontrolled environments where mechanical stresses such as vibration are common.

These stresses degrade the crystalline structure increasing refraction and decreasing transmission. And as the window becomes weaker it is much more prone to fracture. Even an electrician slamming a panel door closed can cause it to shatter. As a result, the average life expectancy of this type of window, irrespective of whether it is producing valuable data or not, is less than 10 years.

Another factor to consider is whether the intended environment for the window is damp or humid. Calcium and barium fluoride are hygroscopic, even when coated. This means an infrared window made from this material will absorb moisture and, over time, this too will compromise transmission rates and render readings inaccurate.

That leaves polymer based infrared window systems. For the industrial environment, this type of window has many advantages. It is shatter and impact proof, will not degrade in the presence of moisture, UV or vibration and windows made from this material carry an unlimited lifetime warranty. It can also be any size or shape to suit the application.

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