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IR Windows Optics: What’s Available?

Posted on: 30th, July 2018

An understanding of IR cameras, what they can and can’t do, will ultimately lead us to what an IR Window is and the crucial factors you must take into consideration when thinking about investing in them. One of which, considered the most important factor, is the ‘optic’ material that they are manufactured from. Let’s explore…

What is an IR camera?

An infrared, or IR camera is a very clever piece of technology in that it can actually see heat.

Some of you may recollect a very famous movie in which soldiers are seeking an extraterrestrial being using an infrared camera. Although there have been significant advances in the technology of IR, the functionality is demonstrated very well here.

The way that IR cameras work is that they use a completely different part of the electromagnetic (EM) spectrum to the part that the human eye uses. This is known as the infrared part of the electromagnetic spectrum.

The advances in microbolometer technology – which is essentially a sensor within a camera – makes the IR camera an exclusively ‘uncooled’ system. This is a relatively new form of sensor which comes with lots of advantages, including the fact that it removes the need of a cooler due to its runtime extension. These types of cameras tend to operate in what is known as the ‘longwave’ or 8-14μm section of the electromagnetic spectrum.

What materials can be used for an IR Windows optic?

IR Windows – which are used to perform fast and safe infrared surveys of electrical equipment across all industry sectors – require certain materials that are transparent to infrared in the band that the particular camera you are using operates in. At the moment there are three different options of optic material that are typically available:

  • Mesh/polymer combination
  • Hole (port)
  • Crystal

Let’s compare each one in turn…

Mesh/polymer combination optics

An IR Windows optic that is made from a combination of mesh and polymer is a product that can be bombarded with high levels of impact. Although this particular material is very thin, the optics still perform extremely well under the pressure of a hammer, for example. This proves just how durable this particular variation of IR Windows are.

However, the downside of this material is that it does not react well to flames, which means that it can easily melt away, resulting in the optic baring just the mesh and perhaps open holes.

This particular type of optic does cause many problems, as although the image looks great when the mesh has been focussed out by the camera, if the target is very close to the panel inside face, the camera cannot fully focus. This causes many issues, as it can result in a rippling type effect on the final image.

Hole/port optics

The hole/port optic is a solution that comprises of a view port/hole and a fisheye lens. When this solution was introduced, it meant that transmission loss error issues were long gone. This was because the camera itself was effectively inserted into a socket in the panel, turning the port into a hole.

This particular optic material is great for measurement, however, if you look at them from a safety standpoint, they don’t match up to the others. In fact, it can be argued that these ports should not be classed as such at all, as they actually defeat the purpose of a window.

Imagine installing an IR Window/port into a panel and attempting to take an image while exposing yourself to live electrical equipment? The risk of injury is exponential.

Crystal optics

Compared to the previous options, this product has many benefits that far outweigh its failings. In our opinion, this is the best solution to go for when choosing IR Windows optics.

There are many different types of crystal IR Window materials. The most common being germanium. This material is found on your infrared camera lens and can either be purple or orange in colour, depending on the coating that has been used.

Germanium is known in the industry as the ‘grey transmitter’, which means that its transmission loss is consistent across the whole of the infrared spectrum. This factor makes it fantastic for lenses as it modulates the IR signal the same way regardless of wavelength. Also, the addition of anti-reflective coatings (AR) makes windows manufactured from this material extremely good infrared transmitters. Unfortunately, germanium can be expensive, and using this material to manufacture a 4″ IR Window would mean they would would end up retailing over $2000 per unit, which rules it out.

Another material which can be used is sapphire, which is very durable and would be able to withstand a hammer impact. But, similar to germanium, this is still a very costly material.

This leaves two materials, which are both ‘flourides’ – Calcium Flouride (CAF2) and Barium Flouride (BAF2). Both of which have been used as optics in the past, but although BAF2 is highly transmissive and great for measurement, it can also be susceptible to moisture and somewhat toxic.

CAF2 is the least expensive option here and is the optimum IR Window optic material. Although it can be brittle, properly coated CAF2 optics do not degrade over time and any errors in reading caused by the optic can be corrected reliably and repeatedly with a properly configured infrared camera. Taking all of this into consideration, we prefer HydroGARD coated CAF2 over the other options as the positives far outweigh the negatives.

Carbon Flouride is homogenous, meaning that its transmission characteristics are consistent across the face of the IR Window. This means that a properly configured IR camera can correct any errors and provide the thermographer with a truly representative temperature measurement. This material is also optically and thermally transparent and is not only transmissive to IR and visual cameras, but to UV cameras as well.

You can find out more about these three options in our new white paper on IR Windows, which is free to download here: ‘IR Windows 101 – The questions you were afraid to ask‘.

Our white paper will explore each option in more depth, including the problems associated with each, and of course, their benefits.

IR Windows 101 eBook

Are you considering using IR Windows? Then you need to download your FREE copy of our ‘IR Windows 101: The answers to the questions you were afraid to ask’ White Paper today. A decade ago Infrared IR Windows were very much in their infancy, but today things are very different.

Download Now

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