Aside from references to the popular 1987 movie Predator, how thermal imagers work hasn’t gotten a lot of mainstream attention. In the past several years, dropping prices have seen their increased use in troubleshooting. There’s a good reason for that. Thermal imaging has always been in transition. A lot of recent technological changes have really brought these tools into the mainstream. Thermal imaging technology migrated from contact readings to infrared to thermal pictures. As it did this it also became more affordable. Thermal imagers used to cost upwards of $35,000 not too long ago! Today you can pick up a tool in this category for under $300. They even make them as accessories for your smartphone. That’s a considerable price swing, but one that is great news for tradesmen who use them—or who now can for the first time.
How Thermal Imagers Work to Identify Heat Sources
I want to go over the uses for these infrared heat-imaging tools, but first, it’s good to understand just how thermal imagers work. After all, that’s more or less the point of this article. They are incredibly complex and “smart” devices. A thermal imager is essentially a single spot temperature gun on steroids…and then some. If you think of a single spot thermometer as a black and white photo, the thermal imager is a full-color high-definition movie. You’re taking hundreds of single spot readings and tying them together—and you’re doing that every second. Each measurement is translated into a color, which the tool then puts together to generate a heat map. It’s like a weather map, and it delivers a temperature profile as well as an image of the target.
What Makes Thermal Imagers Complex
Specifically, each pixel in the array of a thermal imager responds to infrared energy. The way it responds to what it measures correlates to the temperature picture it produces. The “magic” comes in creating a readable temperature map. Because each pixel has its own reaction to the energy, you have to turn all of that information into something that makes sense on the viewable LCD screen. It’s quite involved and pretty significant.
Another thing that adds to the complexity of how thermal imagers work is that the sensors on thermal imagers are, as you might expect, very sensitive. Just by holding the product, your skin will warm it up by 0.1 degrees Celsius. This will impact the temperature reading.
A good thermal imager works by compensating for every increase temperature that comes into the product from the environment. It doesn’t really matter if it’s the heat or cold outside or a temperature change caused by holding the tool. Even prolonged use of the laser pointer on some of these tools can affect the heat measurement if not taken into consideration. This whole internal/external temperature dance is based around the array which is located within the housing. Any time there is anything that impacts the housing, the array compensates.
How Different Types of Thermal Imagers Work
Thermal devices come in three basic flavors. There are the “simple” infrared thermometers that take an average point source measurement. (The technical term for these tools is pyrometer.) There are also visualization tools that use pyro-array technology. Finally, there are microbolometers.
The real breakthroughs have occurred in the middle category. Pyro-array devices can use less expensive technologies to bring thermal imaging capabilities to lower price points. These new visual thermometers feature a pyro-electric array that can generate a thermal image similar to how a microbolometer does it, but at a reduction in manufacturing costs. The technology is based on a combination of single sensors that work together to create the thermal map.
Thermal Imager Limitations
There are limitations to what these newer inexpensive arrays can do. For starters, there’s an upper limit to how big you can make them, so you can’t get as clean and crisp a picture at larger resolutions. To get this higher resolution, you need to bump up to an actual microbolometer. Microbolometers also bring more sensitivity, so they do a better job of determining smaller temperature variances. As an example, a microbolometer can have a resolution of .10 degrees Celsius or better, while a typical pyroelectric array’s resolution is .25 degrees Celsius.
Thermal Imaging Gets Affordable
Just as manufacturing costs (and consequently, prices) keep dropping in the digital imaging world, the same thing keeps happening with thermal imaging. The trend seems to be twofold. First, thermal imaging is becoming increasingly affordable. Since more professionals know how thermal imagers work, these tools are seeing more use. Second, significant advancements and features are making them easier to use.
Visual IR Thermometer (Pyro-array) 
Thermal Imager (Microbolometer) 
Infrared Thermometer (Pyrometer)
Integrating Photography for Better Resolution
An example of this would be the newest products that overlay the colorful infrared color temperature maps on top of the actual images. Unlike older models, the newest ones are also focus-free. Features like this make it incredibly easy to use the device and understand what it is you’re measuring.
Electronic compasses have also become a new feature, that lets you document and distinguish which direction or panel you were inspecting at the time of the recorded measurement. Some of the new tools are also quite rugged and can take a drop.
Show Your Work
In addition to becoming more affordable, the attraction to thermal imaging technology is that you can really show your work. That helps in documenting and troubleshooting, and it’s a big step forward in inspection and maintenance since it gives you the ability to get really specific about when and why to replace or repair a particular device in a way that simply wasn’t available before. Just like inspection cameras, thermal imagers are now finding their way into hands that previously couldn’t afford them.
Knowing how thermal imagers work will help you determine if your company should pick one up. As the tools continue to drop in price, I think we will begin to see more and more uses surface for these incredibly handy tools.
Who Uses Thermal Imagers?
If you’ve never been interested in the use of a thermal imager, you probably aren’t likely to start now, but there are some very key areas in which these tools are starting to become very integral—particularly as prices continue to drop and the technology becomes more accessible to more and more tradesmen.
Industrial
The industrial applications for a thermal imager are nearly endless, but the primary use is for in-house maintenance inspections. You could lose a line for a week because of a loose wire or a blown or malfunctioning fuse. A bearing could be going bad in a motor that runs a critical function. All of these are problems you simply wouldn’t be able to see by eye but would be able to catch during a thermal scan. Without a tool that can “see” these problems before they progress to a point of failure, you won’t spot the problem until it’s too late.
Electricians
Electricians, both commercial and residential will do an electrical system installation and use these to prove their installation or repairs were done correctly. Companies like Fluke include software to let you generate a custom report. In this way, you can document your work and deliver documentation on a panel or other electrical system.
HVAC
HVAC and mechanical contractors will use this imaging tool in a similar way as electricians, but their application is different. They may use the tool to monitor HVAC systems, motors and pumps and check them for points of failure.
Automotive
This was a surprising category but one that makes a lot of sense. With newer, less expensive, visual thermometers, in particular, you can use these tools to see problems with a blocked condenser or a malfunctioning rear window defogger. It immediately lets you see which parts are warm and which aren’t. With vehicles, there are simply areas that are inaccessible without a lot of labor, and a tool like this can be invaluable to have in a shop to help in troubleshooting and diagnostics.
Firefighters
Many people will recall images of firefighters using fancy scanners to navigate their way through a burning building and identify people within. These tools also utilize the same basic principles as thermal imagers. The difference is that they don’t need precision instruments to tell them the exact temperature. Rather, they need the more advanced capability to distinguish contrast so as to identify body heat from an adjacent burning room. (This is essentially the ability to adjust the dynamic range to cancel out the flame.) They also care a little bit more about durability and heat tolerance. After all, when was the last time you needed a tool housing to withstand temperatures in excess of 200 degrees Fahrenheit?
Pro Tool Reviews wants to thank Jay Choi, general manager for Fluke, for taking the time to answer our questions about thermal imagers and the ways in which this technology is changing and growing. If you are a product manager and have an interesting story to share about how a particular tool or technology works, please feel free to send us a note at [email protected], so we can consider using it in a future article or contact you to get more information.
