A thermal imaging camera must be well-calibrated, right from the onset. Using an uncalibrated one is like using a saw with blunt teeth. Make no mistake about it. Think of it as you would a 12-inch ruler, or one foot. Every grader in America knows what a ruler is. However, truth be told, not everyone knows one inch used to be a rough estimate. And that exactly shows why making sure you’re using a standard method of measurement in your thermal inspection is wise. Or you’ll end up shooting yourself on the foot.
Now, the word inch comes from the Latin word uncia (meaning: one-twelfth) and has been handed down as a unit of measure from the British to the Americans. Centuries before, one inch is generally understood as the width of a human thumb. But that measure sure is confusing as everyone has a different set of thumb, right? Eventually, six nations - America and the UK including - tired of all the erroneous calculations amidst a lack of standard agreed in 1959 to set things straight. And that’s how you get an inch as exactly 25.44 millimeters.
Of course, setting a thermal camera to a standard is tricky. To boot, you need blackbodies to get it done. It’s not like you’re measuring a piece of wood for your DIY side table project. It’s a lot more complicated than that. Arming yourself therefore with ample knowledge is key to a most successful thermal imaging camera session. Here’s the lowdown to get you started in the right direction.
Your Thermal Imaging Camera and Calibration
Let’s face it. Your work is only as good as your tools. No matter what industry you’re in. You need your tools to be as sharp as ever. Think about it. A chef without the benefit of sharp knives will not only take time to finish the cooking but he’s bound to come up with paltry dishes. A world-class artist without the benefit of a good brush to create art would be as limited.
The same goes true for electronic measurements, and perhaps even more so. Unlike rugged hand tools, any less-than-optimal reading on an electronic device is hard to uncover. A good example here is a multimeter. If your multimeter readings are off-target, you will discover such an error would undermine your work in the long run. And disastrously.
That is exactly why over time, you’ll have to calibrate your multimeter every now and then. Technically:
- Calibration: is the finetuning of the measurement values of measurement equipment to reflect the values set to a calibration standard of known accuracy.
Simply put, calibration is setting your infrared camera (IR) to a standard. So the million-dollar question is should you calibrate your thermal imaging camera? The short answer is yes. You should.
But hold your horses. Before you lay a finger on your handy infrared scanner, take heed. You could end up in a far worse place than when you started if you’re not careful.
Calibrated or Uncalibrated?
Right off the bat, calibrating your thermal imaging camera may come as a surprise to you. But for your infrared camera to function best, it has to accurately measure thermal radiation. Or, if not, your resulting data is off-tangent. In the process, your survey of the area is highly questionable.
Fortunately, most thermal cameras in the market today are already calibrated. This means, just like most electronic measuring devices (e.g., multimeter), a brand new infrared camera is set to factory standards. Over time, however, calibration shifts may occur due to electronic component aging.
To a large degree, using such a poorly calibrated infrared device would be disastrous on your part. Not only will your results be compromised, but also your reputation could be at stake.
Take note, however, that a number of infrared cameras are inherently not temperature calibrated by the manufacturer. Usually, these are old-school infrared cams that are used to determine the hot and cold regions of a particular scene relatively. Typically, these are the monochrome image black-and-white thermal imaging cameras of old. These infrared cameras, in spite of their apparent lack of technical capacity, serve a purpose. You can use them in quantitative inspections instead of qualitative ones.
Of course, if you want to be as accurate as possible using a more thorough approach is paramount. And that’s where honest-to-goodness manufacture-set thermography cameras are spot on. These can perform absolute temperature measurements.
So before you open your thermal camera, know first and foremost:
- Is your thermal camera calibrated or uncalibrated by the manufacturer?
If your thermal inspection is for qualitative purposes, you may need to check on the calibration of your infrared camera every now and then.
How to Perform a Calibration Check Yourself?
In general, your brand new thermal camera is factory calibrated for at least a year. Therefore, it’s safe to say that your infrared device is accurate within that period. But from time to time and especially after that period, re-calibrating your device should bid you well.
However, there’s a hitch — and one you should consider. Calibration can only be best performed by the manufacturer itself. Why? Simply because it’s a complex process that needs state-of-the-art technology.
To make the calibration process as effective and as efficient as possible, you must perform a multi-point calibration. This means getting temperature samples spanning the entire temperature range of the infrared camera in question. We’re talking about the lowest range (coldest) to the highest range (hottest).
To do that, the process would need a series of blackbodies that emit at different temperatures. As the temperatures of these black bodies are known, subsequently checking them on your thermal camera reading should be a matter of direct comparison. Already, that process is taxing by itself. To add burden to all that, multiple temperature samples from different blackbodies must be presented in succession. Plus, you’ll have to take into account the temperature drift that will ensue due to the heat dissipation.
Manufacturers employ the use of a robotic arm that allows a particular camera to be presented to a series of known blackbodies set at a specific temperature. Small wonder a high-tech calibration laboratory is built for that specific purpose. All this is telling you getting your thermal camera calibrated at home is not a good idea. Assuming you’re bent on getting the best results possible.
The good news is you can actually do a calibration test on your own thermal imaging camera. Even better, if you’re infrared device is out of calibration, it’s far too often out by a lot. However, bear in mind that a calibration test is just the exploration side of the equation. It’s not meant to undo the damage and recalibrate your infrared device.
To do a calibration test, you need to deploy targets with known temperatures. Here’s the tricky thing. So the idea is to check if your infrared imaging camera’s reading would correspond to the known temperatures at hand. It’s like the calibration laboratory to some extent.
Usually, two of the most common reference points are melting ice and boiling water. As important as it is to you to arrive at accurate infrared camera heat signatures, you should ensure that your reference points are as reflective of their known temperatures as possible upon reading.
What we mean by that is boiling water should stay at about 100°C (212°F). In other words, you need to ensure water is really scalding hot and not just demonstrating a few bubbles to the surface. Added to that, you should make it a point that condensation on the lens of your camera isn’t affecting the reading.
Additionally, your melting ice should reflect a temperature of about 0°C (32°F). To do that, you can use melting ice cubes taken directly from the fridge. To that end, some water should get the action going.
Before you do that, make sure you’ve set the infrared camera’s emissivity to 0.96. That should ensure the most accurate reflection of the scene. However, if you find that your thermal reading is a bit off, don’t fret. Depending on your thermal imaging camera, you should be able to factor in your camera’s accuracy to the equation.
Check your manual. A camera with a +/- 2°C means a reading of boiling water that comes out as 98°C - 102°C (208.4°F - 215.6°F) is still an acceptable result. Then again, you should ensure the parameters of your scene are all set. If not, you’d be compromising the calibration test. The same holds true for your melting ice. A reading of 2°C is still acceptable given your infrared camera’s accuracy.
Once you find out that your thermal device is not working properly, getting in touch with the manufacturer should be best. And this is where the right manufacturer matters. Indeed, customer service is a treasure trove. Giving you the calibration your thermal imaging camera needs.