A thermographic inspection is conducted to detect abnormal temperature differences in electronics equipment. This is typically performed as part of a broader Preventative Maintenance (PM) effort to capture failures before they occur. The thermographic inspection is especially useful for detecting loose electrical connections or overloaded circuits. The I^2R losses due to excessive resistance show up brightly on a thermal image.
An essential inspection tool is the thermal imager. To better understand the imager’s capabilities, consider the image of man’s best friend included as Figure 1. It’s a good place to start as we can explore the camera’s sensitivity and resolution. Here, the rat terrier’s nose has a temperature of 70 °F while her inner ear is approximately 102 °F (normal body temperature for a dog). The camera’s fine resolution even shows the color of her whiskers. Note that this image includes a temperature scale on the right-hand side for ease of temperature reading.
Figure 1: Thermal image of a little dog. Her nose is a cold 70 °F while her dark-red inner ear is a normal 102 °F body temperature.
The Figure 1 image was taken using an older Fluke Ti32 with the images processed using Fluke SmartView Classic. Fluke suggests the TiS55+ as the modern replacement.
Tech Tip: The thermal imager has a wide variety of uses ranging from electromechanical inspection all the way to a human and veterinarian and diagnostic tool. Be sure to visit the American Academy of Thermology for more information about the health benefits of thermal imaging.
What are the steps for a thermographic inspection?
As a former military technician, I have been involved with many thermographic inspections. They all follow the same steps:
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Energize the equipment so that the components reach normal operating temperature.
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Ideally, we then take an image of operating equipment. If this is not feasible, it may be necessary to quickly turn off the equipment and then gain access to the space of interest. Be sure to follow all applicable local, state, and federal laws as well as Lock Out Tag Out (LOTO) procedures established for your facility.
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Take a thermal image of the equipment.
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After all images are taken, the inspector will review all images and write a report describing all discrepancies. These are often rank ordered from critical immediate fix issues to slight problems that should be addressed at opportunistic period in the near future.
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Based on the nature of the discrepancy, and as time permits, service personnel will repair the equipment to eliminate the hot spots.
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Today’s inspection serves as a baseline for future inspections.
An example is shown in Figure 2: Here we see a residential circuit panel with a circuit breaker that appears significantly hotter than the others. The infrared image is shown on the left while the corresponding image is on the right.
Figure 2: Side by side images of a breaker panel showing infrared and normal. The upper-left dual-ganged circuit breaker is hotter than the others.
Tech Tip: Thermal imaging cameras such as the Fluke Ti32 have two digital cameras; one for infrared and one conventional color image; both shown in Figure 2. Taking a picture activates both cameras simultaneously. Immediately after the image is taken, the camera allows the inspector to embed a voice recording into the file. A typical message would include the locations and any observed abnormalities. These three pieces of information are essential for the inspector to construct a full report noting all discrepancies. Note that the associated PC-based imaging software is built to automate and streamline report generation.
How do we interpret a thermal image?
This is a complex topic well beyond the scope of this brief article. However, we can look at a few common errors. Returning to Figure 2, we can see that something is not like the others. Without question, the upper-left circuit breaker is hotter than the other breakers.
But is it defective?
In this case, we can look at the absolute temperature on the side of the graph. The hot spot is about 77 °F. That’s not excessive. For comparison, consider Figure 3. Here we see my hand in front of the circuit breaker. Relative to my hand, the circuit breaker is cold. While that is not a definitive answer, a circuit operating at less than human body temperature does not raise any immediate concerns. Stated another way, not all thermally bright images are bad. This may be a situation where a high-quality camera with high thermal resolution can misguide an inspector.
Tech Tip: How hot is too hot? One way to answer this question is to consider the wire insulation. Obviously, breakdown of the wire insulation is unacceptable. The answer depends on the type of wire, however as a general statement 150 °F is too hot. Another way to view this situation is to look at the relative temperature. For example, all elements in a three-phase system should have the same temperature. Any deviation of more than a few degrees could be cause for concern. For more information consult an inspection expert or attend a thermographic training session. One place for specialized training is the Infrared Training Center.
Figure 3: Image of the breaker panel taken at a three-foot distance. The circuit breaker introduced in Figure 2 is cold when compared to the author’s hand.
Another interesting problem involves reflections. For example, consider Figure 4. The upper bus bar (ground) appears to be hotter than the surrounding components. In reality, this is thermal reflection of the operator. This particular image was caused by my open palm positioned slightly to the side of the camera.
Figure 4: The upper bus bar in the thermal image appears hot. This is a thermal reflection – an image of the camera operator.
Parting thoughts
This engineering brief provides a basic introduction to thermal imaging. It is an invaluable tool for preventative maintenance as it can identify electrical problems long before symptoms appear. While not covered, the tool is also an excellent way to identify mechanical problems such as an overheated bearing. It is also useful for energy efficient initiatives such as locating thermal leaks.
Best Wishes,
APDahlen
Return to the Industrial Control and Automation Index.
About this author
Aaron Dahlen, LCDR USCG (Ret.), serves as an application engineer at DigiKey. He has a unique electronics and automation foundation built over a 27-year military career as a technician and engineer which was further enhanced by 12 years of teaching (partially interwoven with military experience). With an MSEE degree from Minnesota State University, Mankato, Dahlen has taught in an ABET-accredited EE program, served as the program coordinator for an EET program, and taught component-level repair to military electronics technicians. Dahlen has returned to his Northern Minnesota home and thoroughly enjoys researching and writing educational articles about electronics and automation.
Highlighted Experience
Leveraging his military engineering experience, Dahlen provides unique insights into rugged and reliable electronics solutions suited for extreme environments. His articles often reflect the practical, hands-on knowledge gained from his time in the U.S. Coast Guard.
Questions
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Define preventative maintenance.
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Describe how the thermal imager may be used as part of scheduled preventative maintenance.
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With respect to a thermal imager, what is meant by the term non-contact?
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With respect to a three-phase system describe a normal and an abnormal thermal image.
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Describe a thermal reflection and how it may cause inaccurate temperature readings for a flat bus bar.
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Identify the steps required to perform a thermographic inspection of your facility.
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Perform product research on thermal imagers. Identify and describe at least three specifications directly associated with the thermal camera.
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What is LOTO and how does it impact the thermographic inspection.
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What does the electrical property of I^2R have to do with thermal imaging?
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Identify the unique safety hazards associate with a thermal inspection.
Critical thinking questions
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Locate the advertisement for a thermographic inspection service. Describe the advertised benefits for your facility.
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A thermal imager is a significant investment. Compare the cost to the financial impact of down time caused by a missed thermal event.
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Research the term emissivity and describe the impact on a thermal imager.
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Suppose you could thermally image the windings of a three-phase motor. Describe the attributes of a good motor.
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Research application of the thermal imagers. Describe at least 3 additional applications not addressed in this article.
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Research and then describe at least 3 actions that are part of a preventative maintenance for an industrial facility. Construct a chart showing the cost of implementation relative to the potential to discover problems before they occur.