The Case for Thermal Imaging

Fri, 04/08/2011 - 11:42am
JOEL HANS, Associate Editor, Industrial Maintenance & Plant Operation (IMPO)

Thermal ImagingIn many ways, thermal imaging represents an opportunity to see your plant in a whole new light. It’s a revolutionary technology, one that allows manufacturing processionals to conduct a range of tasks, such as increasing efficiency in automated environments, detecting leaks in malfunctioning equipment, and conducting predictive maintenance. Unfortunately, the technology is considered fairly new, which means it’s not always cheap. To accommodate any business, the companies responsible for the world’s best thermal imagers have created wide portfolios of products in all price categories, allowing any manufacturer to make just the right purchase for their needs. Of course, that begs the question: What should you look for, and how do you use it?

To help answer these questions, we sought out the help of thermography experts to shed light on some of the common applications associated with thermal imaging.

First thing’s first. Michael Stuart, Senior Product Marketing Manager and Level III Thermographer with Fluke, wants to remind everyone that they shouldn’t simply buy an imager and get to work. “Err on the side of safety,” he says. “Anybody that’s doing this kind of work — especially around dangerous equipment, electrical equipment, or process equipment — needs to be qualified in order to do it. We don’t want the janitor to open up junction boxes.”

Case #1 A manufacturer has been having issues with their electric conveyor motors, namely breakdowns and overheating.

According to engineers with FLIR, a few features can make a difference in surveying a large number of similar components, while saving users time. By turning the camera to “manual adjust” and fixing the scale to a motor that is working normally, users can find any motor running hotter or colder in different colors. FLIR engineers explain: “If your camera has an Isotherm or Color alarm, you can use this feature to automatically show you areas of the image above a threshold temperature. Then you just have to set the threshold temperature and look for the alarm color.”

Stuart, from Fluke, has more direction on where users might look in order to find problem components: “There are various potential points of failure where thermal imaging would be useful. Number one would be the physical electro-mechanical system: the drive motor itself,” Stuart explains. “You can have various problems on that motor. For example: bearing issues, electrical connection issues in the junction box, or impeded airflow if the cooling vents are clogged up with dust or dirt. Thermal imaging can be useful for all of those things, to discover where there’s a problem.

“A lot of the time you’re doing comparative thermography. You’re not looking for absolute temperatures, unless it’s exceeding a nameplate rating. That’s an obvious warning sign. But most of the time it’s a lot more subtle, and the person using the camera has to look for unexpected thermal patterns, which indicate something is amiss.”

Case #2: When performing an audit of a plant’s energy consumption, maintenance staff determine that the HVAC system is using more electricity than needed to cool the facility to the desired temperature.

Dealing with HVAC systems is a little different than thermal imaging of electrical systems, although there are some shared components. Stuart explains, “When you’re inspecting a system for air leakage, you are not physically seeing the hot air or cold air with a thermal imager. That’s not possible with long-wave thermal imagers. What you’re seeing is the effect of the hot or cold air on the surface that’s immediately near where the leak is. Typically, when you have a duct leak of some sort, you have enough pressure behind that leak, and there is enough of a temperature difference between the inside and outside of the ductwork. The thermal imager can see a surface pattern that looks like either hot or cold fingers streaming out of the area. That is a rather typical pattern for this type of problem.”

FLIR engineers say the advantage of using a thermal imager is that they let you inspect all of the systems involved in the heating and cooling of a building — electrical, mechanical, and duct work — as well as the building envelope itself.

They explain, “You need a thermal imager with good all-around performance. For instance, you need good sensitivity to find the small temperature differences that betray leaks in ductwork or missing insulation. However, you also need a broad temperature range to quantify temperature variations in electrical and mechanical components — look for 250 degrees C or greater.”

Case #3: A manufacturing plant is having electrical issues that are shutting off lights and important machinery.

According to FLIR, infrared cameras are ideal for determining which electrical components are causing issues. Typically, components on the verge of failure will heat up, or have a different thermal signature compared to properly-functioning ones, which can be easily monitored and recorded with a thermal imager.

“But,” says FLIR, “finding problems is only the first part of the equation. It’s also important to quantify their severity so that you can prioritize your maintenance efforts. The best way to do this is by comparing temperatures between components under the same load. Using a camera like the FLIR T-Series, you can measure multiple spots and have a difference calculated on the image to make these comparisons in the field. In addition, you can wirelessly add the electrical load data gathered from a clamp meter data via MeterLink from some Extech clamp meters. This gives you all the information you need to make the right call.”

According to Stuart, “Thermograhy has long been known as a great tool for electrical work. One can scan connections, conductors, and various other electrical components to look for hot spots or cool spots that you don’t expect. You’re looking for places where you might have a high-resistance connection. You also look for potential overload situations, where you’ve just got too much current going through that particular conductor or component. When you see this, it may be indicative of some problem upstream or downstream. What you see with the thermal imager is not always the root cause of the problem — sometimes it is only a symptom. Understanding how the equipment you are inspecting is supposed to work under normal conditions is critical.”

In order to do work on some smaller electrical components, users need an imager with a spatial resolution (IFOV) that is capable of seeing small details, which may only have a relatively small temperature difference relative to the surrounding area. “Almost any imager out there will be able to tell you if an object is hot or cold,” Stuart says, but in order to properly diagnose a problem, users will need to have an imager with more capability than what many entry-level cameras presently offer.

What to Look For?

Even is your plant is suffering from a situation explained in one of the three potential cases above, it’s hard to know what to look for when purchasing a thermal imager. Specification pages can be filled with dozens of obscure figures and numbers. Says Stuart: “A lot of it is dependent on the application, or the set of circumstances. Key specifications that should be considered from a infrared standpoint are the focal plane array (FPA sensor size). That’s the physical sensor that senses the infrared energy coming in and converts it into an image that we can see. You will typically see this specification listed as 160 x 120, or 320 x 240. The more rows and columns, the better the expected performance.”

While the 320 x 240 sensor provides four times as much data as the smaller 160 x 120 version, it’s important to remember that the FPA size is not the only important specification for good image quality. The Spatial Resolution, or IFOV of a device  — its instantaneous field of view — can be translated to the smallest detail the device will resolve. If one wants to see all of the small details in the thermal image, which will help more accurately diagnose what is going on, this figure is important.

Finally, users should look at the Thermal Sensitivity (or NETD) of the thermal imager. The lower the number, the better the device’s ability to detect small differences in temperature between two points. How low does one need to go? Stuart says, “For elecro-mechanical inspection and maintenance? Typically if you have a thermal sensitivity of 100-200 mK or better (which means lower), that is more than adequate. I wouldn’t go out there and buy a product at 500 mK, however.” Luckily, users can easily and affordably purchase models from = 200 mK (0.2 degrees C) all the way down to = 50 mK (0.05 degrees C).

So if you’re looking to get into the world of thermal imaging, perhaps it’s time to start thinking about all your potential applications, and start researching. Attend a training session, which are offered by both FLIR and Fluke. Sometimes it pays to be on the forefront of new technology, especially when it comes to the continuous improvement of your facility’s maintenance practices.

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