Thermal Imaging for Industrial Testing

By Deepshikha Shukla

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This article explains the role of thermal imaging cameras in industrial applications, followed by their comparison with IR thermometers, working principle and buying tips.

For manufacturing and other industries using heavy electrical and mechanical machines, thermal imaging is a one-time investment in continuous machinery testing for production level and efficiency. Thermal imagers are one of the most valuable diagnostic tools for industrial applications. These identify anomalies that are invisible to the human eye, thus allowing necessary corrective measures to avoid costly system failures.

High-power transmission line inspection by thermal imaging cameras
Fig. 1: High-power transmission line inspection by thermal imaging cameras (Courtesy: www.test4less.co.uk)

Thermal imaging cameras record the intensity of infrared wave radiation (part of EM waves) and convert it into a visible image. This helps users to find out when and where maintenance is required. Electrical and mechanical installations tend to heat up before failure. By identifying those hot spots with a thermal imaging camera, preventive actions can be taken. This can avoid costly production breakdowns or, even worse, fire. Thermal imaging cameras can scan temperature distribution throughout the entire surface of machinery and electrical equipment without requiring contact.

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Thermal imagers find application in almost every industry including defence, manufacturing, electronics, electrical, mobile, automotive and petrochemical. Applications for electrical systems can be divided into two categories: high-voltage installations and low-voltage installations. Thermal imaging cameras can be used for inspection of high-voltage substations, switchgear, transformers and outdoor circuit breakers from a safe distance without entering the risk zone. In low-voltage installations, thermal imaging cameras help to locate hot spots of loose connections, load imbalances, corrosion, increase in impedance to current, etc.

 Modern thermal imaging cameras are small, lightweight and easy to use
Fig. 2: Modern thermal imaging cameras are small, lightweight and easy to use (Courtesy: www.50northspatial.org)

The temperature of mechanical components rises as these wear out and become less efficient. This increases overall temperature of equipment, causing these to fail. Thermal imaging cameras can monitor many mechanical systems including motors, couplings, gearboxes, bearings, pumps, compressors, belts, blowers and conveyor systems.

Inspection of a substation revealing overheated components
Fig. 3: Inspection of a substation revealing overheated components (Courtesy: www.bsria.co.uk)

There are many other areas where thermal imaging cameras play an important role. These include flare detection, tank-level detection, hot spots detection in welding robots, aeronautical materials inspection, moulds inspection, and inspection in paper mills, pipe work in refractories and petrochemical installations.

Inspection of a substation revealing overheated connections (Courtesy: www.bsria.co.uk)
Fig. 4: Inspection of a substation revealing overheated connections (Courtesy: www.bsria.co.uk)
Suspected roller and overheated bearing (Courtesy: www.bsria.co.uk)
Fig. 5: Suspected roller and overheated bearing (Courtesy: www.bsria.co.uk)

IR thermometers are reliable and very useful for single-spot temperature readings. However, when scanning large areas or components, these may miss critical components that are nearing failure and need repair. Thermal imaging cameras, on the other hand, scan entire components, giving you instant diagnostic insights with the full extent of problems. These are easier to use and find problems faster with higher accuracy.

How thermal imaging cameras work

L) IR thermometer and (R) thermal imaging camera (Courtesy: www.bsria.co.uk
Fig. 6: (L) IR thermometer and (R) thermal imaging camera (Courtesy: www.bsria.co.uk

The hotter the object, the more its infrared radiation. Infrared energy coming from the object is focused by the optics onto an infrared detector. The detector sends this information to a sensor for image processing using complex calculations. The sensor translates the data into an image that can be viewed on the LCD screen. Each pixel of the image is a measure of the temperature at different points. This is achieved by complex algorithms performed in the thermal imaging camera. If the resolution of an image by a camera is 60×60 pixels, it is equivalent to the use of 3600 IR thermometers at the same time.

Choosing the best

Thermal imaging cameras are a long-term investment. The safety of entire installations and operating people relies on them. So you need to choose a camera that serves your purpose over a long period of time. The things you should look for are hardware, software, accessories (lens and display), after-sales services and training.

As regards their use, you may face a few challenges. Honeywell experts explain these as follows: Thermal properties of materials depend on their compositions. In contrast to insulators, metals heat up quickly. Differences in thermal conductivity can lead to large temperature differences under certain circumstances. So always check the thermal conductivity of the material and its surroundings before inspection.

Emissivity is another important factor that is highly dependent on material properties. It is the efficiency with which an object emits infrared radiation. You should set the right emissivity. Else, temperature measurements will be incorrect.

Difference in emissivity causes difference in intensity of radiation (Courtesy: www.bsria.co.uk)
Fig. 7: Difference in emissivity causes difference in intensity of radiation (Courtesy: www.bsria.co.uk)

Some materials have mirror-like reflection properties, especially if these are polished or non-oxidised metals. These reflections can lead to misinterpretation of the thermal image. Therefore choose the right angle to avoid such reflections.

Ambient temperatures can mislead the actual temperature readings. High ambient temperature may increase temperature of the entire object, thus masking the actual hot spots. Low ambient temperature may cool down the hot spots.

The right combination for the best detection is high resolution, low thermal sensitivity, high accuracy and LED lights in your camera.

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