Infrared Camera: Must Read This Before you Buy any IR Camera

An infrared camera, which is also known as a thermal imaging camera or thermographic camera has become an integral part of everyday troubleshooting and diagnostics for a wide range of industries including electrical, plumbing, restoration, pest and building to name a few. Every day we receive numerous telephone calls from prospective customers, looking to buy an infrared camera for various reasons and the same question pops up repeatedly – “Which is the best infrared camera for my needs” The question itself is a very general one, as many factors have to be taken into account and although we stock a very wide range of Thermal Imaging Cameras, different thermal imaging applications have to be considered in order to select the most appropriate device.

Infrared Resolution:

This is the most widely known feature of most infrared cameras, and is the most discussed element of the infrared camera specification. Usually, this is expressed as 2 numbers multiplied by each other. For example, the Testrix 322-M has an infrared resolution of 160 x 120 which means there are 160 pixels (or temperature measurements) horizontally, and 120 pixels vertically. Multiply the numbers together and that gives the number of pixels in the infrared thermal image, so 160 x 120 = 19,200 pixels. Each one of these pixels represents a single measurement, so the more infrared pixels there are, the better the image quality will be, and the smaller area of temperature can be measured.

Entry level infrared cameras, such as the 321-F, or the FLIR C3-X have a lower infrared resolution, which means that you have a resolution of 128 x 96 or a total of 12,288 pixels (128 pixels horizontally, multiplied by 96 pixels horizontally). These infrared imaging cameras are generally at the cheaper end of the market, close to around $1,500 and are designed for entry level use. Take a look at the image taken with a lower resolution camera, the 321-F at an infrared resolution of 128 x 96 pixels:

This image is taken in a higher contrast palette, known as Rainbow HC. If we take it in a lower contrast palette, such as Iron, which is familiar to many infrared thermal camera users, this is what you get:

There is enough detail to see what the subject of the image is, and to get a general idea of temperature, but finer details and intricate temperature gradients and details cannot be seen.

The Testrix 325-M infrared camera offers increased resolution over the lower level thermal imaging cameras, such as the Testrix 322-M, and even though it still is a simple to use infrared camera, it’s resolution, at 320 x 240 pixels =76,800 pixels quadruples the number of pixels that the Testrix 322-M can deliver. This level of resolution, as recently as ten years ago or less was costing in the region of $12,000 upwards. More pixels equals a better image because in the same field of view, there are more than twice as many pixels. If measuring something like for like – take the dog in the above FLIR C2 image, then the temperature gradients and level of detail will be superior.

At the top of the Testrix 320 Series range, we get infrared resolution of 384 x 288 pixels, so multiplying these numbers together gives 110,592 pixels, which is nearly 34,000 more pixels in total than the Testrix 325-M, and almost SIX TIMES more pixels than the Testrix 322-M. Looking at the below infrared image of the same dog, it becomes very quickly apparent what a difference the increased resolution makes to the infrared camera:

With a 324 x 288 infrared resolution, the dog now has far more temperature gradients and differences highlighted in the image taken with the FLIR E8, even in a lower contract iron palette, note that the image is far sharper and more detailed than the ones taken with the lower series infrared camera:

The most expensive infrared cameras which are readily available can have infrared resolutions of up to 640 x 480 = 307,200 which is four times more pixels than the 320 x 240 pixel cameras. The FLIR T620 and FLIR T640 would be examples of this infrared camera, and these product the best infrared images. See the same dog, but this time imaged at a 640 x 480 resolution:

The amount of detail in this image is far greater than even the 320 x 240 infrared cameras such as the FLIR E8 and the FLIR E60, and this is what higher infrared resolution can achieve. One of the most common questions is based around the difference between different infrared cameras with different resolution and the examples above aim to answer that question to an extent. The principle of how all of the IR cameras in the FLIR range is similar, but the resolution and thermal sensitivity are the things (other than functionality) that change.

Thermal Sensitivity:

Of the things related to infrared imaging cameras, thermal sensitivity is the one thing which is poorly understood. Most customers look at it and don’t fully understand it. Some infrared camera manufacturers refer to this as NETD (noise equivalent temperature difference), and it is a value which is usually expressed in mK (or millikelvin). A Kelvin is equivalent to one degree Celsius, the difference between them being that the scales are different. Zero degrees Kelvin or absolute zero is -273 degrees Celsius (-273.15 degrees Celsius to be exact), so zero degrees Celsius would be 273 degrees Kelvin. The important thing to remember is that one degree on both the Kelvin and the Celsius scales are the same. A millikelvin is equal to 1/1000th of a degree Kelvin or 1/1000th of a degree Celsius (as they are the same), so if an infrared camera has a thermal sensitivity of 100mK, that is the same thing as saying 0.01 degree C. This is the minimum temperature measurement that can be made by the detector. On the face of it, a value of 0.1 degrees C, or 0.15 degrees C or 0.05 degrees C would seem trivial to many prospective IR camera buyers, but there is far more to it than just the minimum temperature difference which the infrared camera can measure.

Take a look at the below images. The one on the left is taken with an infrared camera which has a thermal sensitivity of 200mK (0.02 degree Celsius), and the one on the right is taken at exactly the same infrared resolution, but with a thermal sensitivity of 100mK (0.01 degree Celsius):

Note that although the infrared resolution is the same, the image on the right is superior to the infrared image on the left, due to the fuzzy appearance of the left hand image. This is because of the difference in thermal sensitivity or NETD and becomes much more apparent on images with lower thermal contrast, or in other words applications where the temperature differences are not as great. Usually these applications tend to be building and pest but can be any industry at all. I have been out on site with electrical contractors and seen them have exactly the same problem with switchboards. With the image on the left, or when the thermal sensitivity of the infrared camera is not as good, this affects something known as the signal to noise ratio (SNR) which is what gives the image on the left it’s fuzzy appearance caused by thermal noise. With an infrared camera which has a better level of thermal sensitivity, the thermal noise is reduced, giving a better signal to noise ratio and delivering a smoother image.

It is easy to overlook this fact in favour of infrared resolution, but like most things infrared camera performance is related to more than just one thing. For example it may be tempting to purchase an infrared camera with the same resolution as another, but which is cheaper, and then realise that it has an inferior level of thermal sensitivity and delivers a poorer image than the more expensive unit.

Again, like infrared resolution, thermal sensitivity seems to get better as the infrared camera gets more expensive to an extent, although something like the FLIR E6 has a very good amount of thermal sensitivity for it’s cost. The entry level FLIR E4 has a thermal sensitivity of 150mK, as we go up through the range, this improves. For example, the FLIR E5 improves the level of thermal sensitivity by around 33% with a thermal sensitivity of 0.1 degree Celsius. For those users who may be using their infrared camera on applications where the temperature difference is smaller, then the FLIR E6 and FLIR E8 have the best thermal sensitivity in the more affordable FLIR Ex Series of 60mK, or in other words 0.06 degrees C. This extra thermal sensitivity, coupled with better infrared resolution will lend itself to thermal images with more detail and heightened finer details.

With the FLIR Exx Series, the thermal sensitivity once again starts at 70mK with the FLIR E40, and offers 50mK (0.05 degree Celsius) for the FLIR E50 and FLIR E60. However the BX versions of these infrared cameras cost exactly the same and offer even more sensitivity of 45mK for building and pest type applications. However, the temperature range in the BX versions is lower, with +150 degrees Celsius being the maximum temperature, as opposed to +650 degrees Celsius with the standard Exx series (FLIR E40, FLIR E50 and FLIR E60). The temperature range of the FLIR E4, FLIR E5, FLIR E6 and FLIR E8 allows measurements up to +250 degrees Celsius to me made.

So with that in mind, it is worth looking at both infrared resolution and thermal sensitivity together as both combine to aid the thermal image quality.

Field of View:

The field of view is the area measured through the lens, or in other words what is seen on the screen as a whole. This figure is usually expressed as an angle such as 25° x 19° which means that the horizontal view is 25 degrees and the vertical view is 19 degrees. Think of the infrared camera lens as the apex of a square pyramid and the sides radiating at angles from there. A wider field of view will have a much larger base than the narrow field of view, and therefore contain more objects but as always there is a drawback to this, and it is due to the fact that the amount of pixels remains the same, so the pixel size, which is something called spatial resolution will increase. Therefore the extra field of view will fit more in the image, but the infrared camera’s ability to measure smaller areas of temperature difference will be affected.

Take the FLIR E6 and the FLIR E40 as an example. Both of these IR cameras have the same infrared resolution of 160 x 120 pixels, but different fields of view. This has the effect, if we take a distance of 3 metres into account of the E6 having a pixel size of 15.45mm square, and the E40 pixel size will be 8.33mm square from the same distance. This is because the E40 has a much smaller field of view than the FLIR E6, but the SAME infrared resolution. On the other hand with the FLIR E40 from 3 metres, the field of view will be 1.33 metres x 1.00 metres, whereas the FLIR E6 field of view would be 2.47 metres x 1.85 metres. To make the FLIR E6 have the same field of view and pixel size as the FLIR E40, it is necessary to almost halve the distance to the object from the thermal camera. The FLIR Exx Series can utilize add on lenses to either increase the field of view to 45 degrees, or reduce it to 15 degrees, and the FLIR T-Series can be specified with a number of add on lenses.

Please feel free to call us on 1300 837 874 if you wish to discuss any elements of purchasing an infrared camera and speak to one of our qualified thermographers, who will be ideally placed to offer the best impartial advice.