Every once in awhile, a diagnostic technique that is well established in other sectors of industry will take hold in the automotive world. Case in point: The digital storage oscilloscope (DSO) had been around for many years before being pressed into service as an automotive diagnostic tool. And what a difference it made.
While a digital multimeter (DMM) could do basic measurement of an electrical signal, it could not touch the insight that a DSO provides. Now, many technicians use a DSO as their first line of defense when performing electrical diagnostics.
We might be on the cusp of a similar revolution in automotive temperature measurement. For years, technicians have been using contact probes and infrared (IR) thermometers to help them diagnose drivability and HVAC issues. Like the DMM, these tools provide basic information but don’t give a comprehensive view of the environment. What if we could see an entire temperature context, similar to the way that a DSO expands our understanding of an electrical signal?
The thermal imaging camera (TIC) can do exactly that. TICs have been in use in industrial applications for many years, but were hampered initially by high cost and a steep learning curve for the operator. However, times have changed and there are now user-friendly units available for not much more than what you would spend on a scan tool. It is quite possible that your shop could put this technology to work, potentially lowering your diagnostic times and increasing your technician productivity.
Applications
A thermal imaging camera can be purchased for as little as $1,000. More expensive models will have better resolution and temperature accuracy, as well as features such as built-in digital cameras and voice annotation. (General Tools and Instruments model GTi20 shown)
Many industries are already benefiting from thermal imaging technology. An excellent example is industrial maintenance in 24/7 operations such as oil refineries and chemical plants. In the industrial world, downtime of any kind can be extremely expensive, so an emphasis is placed on predictive maintenance. This means catching failures before they happen and scheduling repairs in such a way that production isn’t interrupted.
Thermal imaging is highly suited for industrial applications because it doesn’t require direct contact with the objects being inspected. More often than not, a machine either can’t be shut down or is difficult to reach. While the plant is in operation, technicians use thermal imaging cameras to take pictures of the various machines and electrical distribution hardware. These images are then analyzed carefully, looking for signs of an imminent failure. Typically, “hot spots” are signs of trouble, such as a circuit breaker in an electrical panel that has developed some resistance and now is running at a higher temperature than normal. This would show up clearly in a thermal image, where the faulty breaker would be portrayed in a different (warmer) color from the surrounding components.
Thermal imaging cameras use memory cards such as these, which can be removed for uploading images to a personal computer.
Thermal imaging technology is making its way into the world of automotive safety systems. Higher-end vehicles are now coming equipped with night-vision capabilities that are based on thermal imaging technology. A supplemental display on the instrument panel shows an infrared image of the driver’s view of the road ahead, making poorly illuminated pedestrians and animals more visible.
For the most part, the manufacturers of thermal imaging cameras have focused their energy on heavy industry and building maintenance applications. However, there are markets such as automotive diagnostics that are essentially untapped but have become more viable now that TICs are much less expensive.
As opposed to an IR thermometer, a TIC gives a view of the entire thermal context of a component and its surroundings. (General Tools and Instruments model GTi20 shown)
How it works
Infrared light is electromagnetic radiation that is invisible to the naked eye, lying on the spectrum between visible light and radio waves. All objects emit infrared radiation, which is proportional to the temperature on the object’s surface. Infrared (IR) thermometers and TICs both use IR detectors to measure the infrared energy being emitted from an object.
An IR thermometer determines the average temperature of a small area and displays the results on a digital readout. In contrast, a TIC will capture an image and paint it with a palette, assigning colors to the various temperatures it detects. The processed image is then shown on the instrument’s display, giving the technician a view of the thermal context of the area being inspected. As you can imagine, the level of information provided by a TIC can make it much easier to identify trouble spots or “anomalies.”
| Emissivity and Thermal Imaging |
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The ability of an object to emit infrared energy is known as emissivity. Emissivity of an object depends on its surface finish and the materials it is made from. Generally speaking, reflective metallic surfaces emit infrared poorly, where rough or oxidized metallic surfaces do much better. This has a direct impact on thermal imaging, because the temperature accuracy of the camera is dependent on the object’s emissivity value. An object with a low emissivity value can fool the camera into estimating its temperature much lower than it actually is. Emissivity of a material is rated on a scale from 0 to 1. A surface that is painted flat black would have excellent emissivity and is rated close to 1. Polished copper, on the other hand, is rated at 0.03, indicating that it has very low emissivity. Good thermal imaging cameras can be adjusted to compensate for low emissivity, which increases the accuracy of its temperature measurement on that object. The emissivity issue needs to be kept in perspective. According to Lou Bellock, director of Product Management for General Tools & Instruments, “The best guide for considering emissivity is a user’s common sense. If a person understands the concept that flat black, non-reflective surfaces are best for accuracy and that bright, reflective metallic surfaces are worst for accuracy; that’s probably 80 percent of the battle.” In cases where greater accuracy is required, the technician can either use black tape to cover a small area of a low-emissivity object, or paint a section with flat black paint. |
An advantage that a TIC has over an IR thermometer is that the TIC is able to record whatever shows on the display on an internal memory card. These images can then be uploaded to a personal computer for use in reports, emailing to customers, etc.
Another difference between a TIC and an IR thermometer is that many TICs have a lens with a manual focus adjustment. The performance of the pixels in the camera’s IR detector is highly dependent on correct focus, which directs the infrared energy on to the pixels. Higher-end TICs may have infinite focus imaging as an ease-of-use feature. Regardless, the technician should be aware that the camera’s infrared detector is not invincible. To prevent permanent damage to your TIC, never point it at the sun or at arc welding processes.
Camera features
Thermal imaging cameras start at around $1,000, and work their way up. The main difference between the least expensive units and ones that cost several thousand dollars is resolution. Similar to the megapixel rating of a digital camera, a higher resolution produces better images at greater distances. Also, more expensive units typically have a higher thermal sensitivity, which is the ability to recognize small differences in temperature.
Just like when using an oscilloscope, it is important to take time to view normally-operating vehicles as much as possible so you know what the thermal images should look like.
Advanced models may also have a built-in digital camera that can take regular pictures simultaneously with the thermal image. Having both images available for viewing can help immensely with identifying the specific objects in the thermal image.
The camera manufacturer most likely will supply reporting software with the TIC. This will make it easier to review the images that you’ve captured and prepare reports on your findings. In the automotive world, this could turn into an excellent supplement to your repair order and final billing to your customer. Imagine how professional this could look to your customers, especially if you are justifying extra diagnostic time.
You should be able to get a TIC that will do most of what you need it to do for less than $3,000. If you’ve got more money to spend, there are numerous other features available that can increase performance and add functionality to your TIC. Shop carefully, however, because many of these high-end options offer limited increases in overall performance for automotive applications.
The temperature gradient is the range of temperatures across a component. This is illustrated graphically when using a thermal imaging camera.
Automotive Diagnostics
One of the decisions you must make when you first set up your TIC for automotive diagnostics is; what palette will you use to illustrate your thermal images? A thermal imager will typically give the user a choice of a number of palettes, which are the range of colors used to represent the temperatures in the camera view.
Regarding the question on which palette is most effective for automotive diagnostics, Lou Bellock of General Tools & Instruments states, “This is purely personal preference. Application independent, I prefer to see hot items ‘light’ (white or red) and cold items ‘dark’ (blue or purple). Therefore, my preference is Feather, which is basically simple rainbow colors.” This is an area where you will want to experiment to determine what works for you. In some situations, you may even decide that a grey (monochrome) display is best.
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Thermal Imaging Tips & Tricks |
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There are some important rules of thumb to keep in mind when using a thermal imaging camera. 1. Focus carefully. As mentioned earlier, the IR detector in the camera will provide inaccurate information with an out-of-focus image. 2. Always try to take measurements at right angles (90o) to the object. This might be a tall order in certain situations, but at least make the attempt. 3. Get as close to the object as possible. This puts more pixels of the IR detector into service on the object you are viewing, which provides a better view of the temperature variations across the object. 4. Centering the object in the display also enhances thermal accuracy. |
The actual temperature of an object will most often be less important than how it compares to a known good component operating under similar conditions. For years, we have heard from oscilloscope users that you have to know what a good waveform looks like before you can identify a bad one. It is no different with thermal imaging; the more “camera time” you spend on vehicles that are operating correctly, the easier it will be for you to pinpoint malfunctions on a problem vehicle.
An example of where the comparison strategy might work is in the case of a noisy axle bearing. In some vehicles, it is a lot of work to replace an axle bearing, and the bearings themselves can be expensive. It also can be a challenge to know for sure which side is causing the problem. In this situation, try taking the vehicle for a robust test drive, then use a TIC to compare the temperatures of the bearing housings. If one side is hotter than the other, you’ve likely found your bad bearing. And don’t forget to record your images for inclusion in your customer report.
TICs often have reporting software included in the kit. This can help organize your images and integrate them into reports.
You might be able to locate a misfiring cylinder by checking temperatures across an exhaust manifold while the engine is running. On a diesel, start the engine cold and watch carefully for cooler sections of the manifold as the engine warms up. Catalytic converter operation also can be confirmed, provided you are able to view the catalyst housing itself and not the heat shield. If the housing is still shiny (not corroded), try spraying a 3-inch wide stripe of flat black high-temperature paint over the length of the converter to increase the temperature accuracy of the TIC.
HVAC diagnosis could get easier if the technician has a thermal imager at their disposal. Think about a restricted refrigerant line, and how much easier it would be to identify one if you could view the temperatures along the entire length of the line. This same dynamic would apply to a condenser, or anywhere else in the A/C system where a pressure drop is taking place.
A TICs view of a diesel engine’s cooling system at operating temperature.
Electrical resistance generates heat. Knowing this, how could a TIC be used to identify poor connections in electrical circuits? For many years, technicians have looked for unwanted resistance in live electrical circuits by measuring voltage drops. This still is the most reliable way to go about this, but what about looking for temperature increases at the connections using a thermal imaging camera?
While this strategy won’t work with low-current circuits, it could work very well on heavier loads such as blower motors, seat heating elements, and rear window defrosters. This would include an inspection of the vehicle fuse boxes and power distribution center, where poor contacts in a relay could cause a temperature increase of the relay housing. Actual temperature would be far less important than just knowing that the specific connection is much warmer than the ones around it.
Flat black high-temperature paint can be applied to components to improve temperature accuracy of a thermal imaging camera.
Carry On, Then
For the most part, the book has yet to be written on the use of thermal imaging cameras for automotive diagnostics. Thermal imaging has great potential, not only for helping techs become better diagnosticians, but also for enhancing their professional image. There is much to be learned about how to utilize this technique, so this could be a great opportunity to do some pioneering.
If you happen to purchase a TIC and start using it for automotive diagnostics, consider sharing what you’ve learned via IATN or similar forums. Sharing of ideas can help us all get better at what we do and will also encourage further innovation. In the end, you and your customers will benefit as we all strive to improve the professional image of the automotive repair industry.
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