Thermal Imaging: Affordable Technology Lets You See a New Light
We’ve all heard the phrase “A picture is worth a thousand words.” As it relates to vehicle diagnostics, this phrase can now be updated to “A thermal image is worth time, money and increased credibility with your customers.” Let’s say a circuit remains active when it shouldn’t be. A thermal image quickly shows the problem and confirms the repair, and you can show it to your customer. It’s quick, efficient and credible.
Before cars had electronic controls, all their malfunctions were something we could see, hear, smell, feel or sometimes even taste (ever sipped coffee next to a car with a coolant leak?). Sometimes we used a test light or a vacuum gauge to pinpoint problems, and for really advanced diagnostics we had an engine analyzer with an analog ’scope as big as a roll away toolbox that would actually let us see secondary ignition patterns.
Today’s diagnostic tools are made for today’s vehicles, and using them effectively requires knowledge and skills that our grandfathers never imagined. We still pay attention to sound and vibration, but most troubleshooting clues are gathered electronically and we see them as data on a display screen. Imagine how much easier and more accurate your diagnosis could be if you could actually see excess current draw or a plugged catalytic converter or a stuck EGR valve.
Recent advances in optical and thermal imaging technology have made this possible. The technologies themselves are not new but the prices are. Today you can buy truly useful inspection cameras and thermal imaging cameras for about half the price of a professional-grade scan tool. They won’t replace knowledge or skill, but they will improve your accuracy and dramatically reduce your diagnostic time.
We’re not going to describe specific tools here because there are just too many to cover. Instead we’ll describe some of their more important features and how you can use them.
Everything in the world radiates energy. That’s because molecules vibrate constantly, and those vibrations generate waves of electromagnetic radiation. The physical distance between the waves (wavelength) depends on the amount of energy. When energy increases, the waves become closer together (shorter wavelength).
The energy that creates visible light is radiated at wavelengths between 400 and 700 nanometers (billionths of a meter). The color red is the longest wavelength we can see, but the discovery of infrared energy (longer-than-red wavelength) in the early 1800s led to the development of the first tool for measuring energy as heat: the thermometer. By 1930, a television camera had been developed for the military that could detect infrared energy more directly and display it on a picture tube. Optical sensors developed in the 1980s made the technology portable, and micro-processors developed in the ’90s made it affordable for civilian applications. Today you can buy a consumer-grade pocket-size infrared camera for about $40.
Professional-grade thermal imaging cameras started showing up on tool trucks almost 10 years ago, and they were expensive. Today these tools are available over a wider price range, and the price generally reflects the tool’s features and capabilities. Some are well suited to automotive diagnostics, and while they are a significant investment, they are powerful diagnostic tools that can save time and improve the accuracy of your diagnosis. more and more techs are buying them and using them successfully.
The most basic thermal imagers are consumer-grade models that connect to a smartphone running an Apple iOS or Android operating system. While these do not really compare to professional tools, they provide a low-cost way to explore thermal imaging before committing to a bigger investment, and they do offer some lasting advantages.
First of all, they harness the processing power of the smartphone. While the image itself doesn’t have the resolution of a professional-grade tool, the app offers a wide choice of imaging and display modes such as still, video, zoom, color range, etc. The more useful models have a regular optical sensor in addition to the thermal image sensor, and the app lets you split the screen to show both the optical and thermal images (see the opening illustration). Some models overlay a line drawing of the optical image atop the thermal image. It’s still a low-resolution thermal image, but the added detail makes the overall picture more useful.
Some consumer-grade imagers can be used with an extension cable. This lets you point the imager into inconvenient spaces, like under the dashboard, while viewing the image remotely on a smartphone or tablet. Even if you end up buying a professional thermal imager later, this small-sized tool can remain useful.
Professional-grade thermal imagers cover a wide price range, but the least expensive models cost less than twice the price of the most advanced consumer-grade imagers. If you’ve ever used a non-contact Infra Red (IR) thermometer, this tool will seem familiar. Most models project a laser dot that indicates the area being scanned, and the display screen will show temperature data along with the image. Most tools store the image as a jpg file on a removable SD card, and some tools can also download the image through a USB connection.
The tools you’ll find at places like Home Depot and other big-box stores are best suited for industrial or residential applications. They can focus to infinity and some have a visual-light sensor to enhance the image display. What they probably don’t have is a big thermal image sensor. A bigger sensor captures a more detailed thermal image, and that’s what you need for automotive work. The spec sheet of most tools lists the pixel size of the display screen, but unless the specs also show the size of the thermal sensor, you have no way to compare it with other tools.
The next step up in price is where you’ll find imagers that are useful for automotive work. Thermal range, accuracy and sensitivity will be more than adequate on all of them. The more important differences from one tool to the next include image display options (zoom, color palate, etc.) that make it easier to detect more subtle temperature differences. The more expensive models include an optical sensor to add visible light details to the image.
When comparing thermal imaging tools, the most important specification is the size of the thermal sensor. By its very nature, a thermal image is fuzzy around the edges, and a low-resolution image can appear as a poorly-defined blob of heat energy. While a built-in optical sensor provides useful detail, a bigger thermal sensor provides a sharper thermal image; that’s where to spend your money. Thermal imagers with a really big sensor can cost as much as a scan tool, but there are several models at lower price-points with a decent-sized thermal image sensor.
Some thermal imagers are made specifically for automotive work. They include built-in software with guided tests and a library of images showing known-good and known-bad components. This can make the tool easier to use right out of the box, and it can also help you explain your test results to the customer.
The next step up in price range buys a tool that can produce thermal images almost as clear and detailed as a photograph. Most are complicated to use and are specifically designed for documenting scientific research or industrial inspections. They are also very expensive, some costing as much as a new car.
What can it do?
Like all automotive diagnostics, most of the problems you can find with a thermal imager can also be found with other tools and techniques. But as noted earlier, a thermal image can visually show you the problem, saving time and giving you more confidence in your diagnosis. For example, the image in Figure 1 shows a warm spot inside the headliner of an Acura MDX. The vehicle’s battery was being drained overnight, and the tech found a 230 mA key-off current draw at the battery. Honda/Acura models are known for faulty cell phone Hands Free Link (HFL) control units that stay active with the ignition turned off, and the thermal image quickly confirmed the problem without removing the headliner to access the control unit itself.
That’s an example of looking for heat energy in places where it should not be. The other obvious technique is to look for heat where it should be, like the exhaust manifold (which cylinder is misfiring?), seat heaters and rear window defoggers (which wire is open?) and even more subtle places like the Mass Airflow Sensor.
Technicians have successfully used a thermal imager to find a dead cell in a battery, a bad idler bearing, slipping drive belt, a clogged A/C condenser or evaporator or radiator or heater core, a dragging brake caliper, and even to verify wheel alignment (by checking tire tread temperature variations). Thermal images are also being used as an effective sales tool. Not only is this a classic case of a picture being worth a thousand words, but the impressive technology also gives customers confidence in their choice of repair shop.
While the tool itself is simple to use, getting a useful image takes a little practice. Thermal sensors work in real time, but it takes a few milliseconds for the software to convert the signal into an image. Most tools auto-range the temperature/color display based on a single point in the center of the field of view. Combined with the time lag, it can be a challenge to hold the tool still long enough to get a stable image, especially with the smartphone tools. A crosshair on the display screen helps you keep the image focused on one point.
Interpreting the image also takes practice. A thermal image looks very different from what we see in visible light. That’s why most tools have an optical sensor and some way to compare the thermal image to the optical image. Most tools also provide more than one color palate because sometimes the detail shows more clearly in a black-and-white image. They don’t all work the same way, so switching from one tool to another requires a little practice, too.
Finally, it also helps to use your imagination. For instance, sometimes it helps to start with everything at ambient temperature because the temperature difference you’re looking for might be only ten degrees. Thermal imagers are sensitive enough to detect that difference, and it’s easier to see when everything else is at the same temperature.
Like the scan tool and oscilloscope, a thermal imager gives you diagnostic speed and accuracy, and in some cases it will show you things you can’t see any other way. If you don’t have one now, you probably will some day, because the capability it gives you is unique. Imagine how much better you can be at your chosen profession when you can see heat.
Borescopes and inspection cameras
Inspection cameras and borescopes have come a long way in recent years. Today you can buy a borescope for less than $15 that connects to an Android tablet or smartphone. Of course, you get what you pay for. Whether it’s a camera or borescope, the most important features of the professional tools are camera size, camera articulation and image size.
Tools designed for automotive work have a camera head that is less than 10 millimeters in diameter, and some are less than 6 millimeters. The lens is designed to produce high-definition close-up pictures, and it should also have some way to adjust the light level at the camera head.
The best units have some method of articulating or rotating the camera head. While this feature puts the tool into a higher price category, it dramatically increases the tool’s utility.
When comparing these tools, pay attention to image capture or image resolution specifications. It takes a high-resolution image sensor to capture a clear image of something that’s only one inch from the lens. Most stand-alone inspection cameras and borescopes offer a photo-zoom feature, but images captured at 640 x 480 pixels will always be clearer than those captured at 320 x 240 pixels.
It’s not exactly X-ray vision, but inspection cameras, borescopes and thermal imagers give you the ability to see things you can’t see any other way. With some imagination and a little practice, it will almost seem like you can see through walls. These tools are not cheap, but the first time you confirm a clogged A/C condenser or retrieve a dropped bolt without removing the timing chain cover, you’ll appreciate your investment. ■
Jacques Gordon has worked in the automotive industry for 40 years as a service technician, lab technician, trainer and technical writer. His began his writing career writing service manuals at Chilton Book Co. He currently holds ASE Master Technician and L1 certifications and has participated in ASE test writing workshops.