Advanced Imaging – March 1998

Predictive Maintenance Heats Up
By Sheldon Liebman

As technology advances, more and more work is being done in the area of early detection. Virus programs keep watch over the actions of your computer to see if behaviors occur that "may indicate" your system is infected. Hard drives contain circuits to alert you if they are starting to fail so you can back up your data before you lose it. For most types of equipment, however, there is no easy way to provide built-in safeguards against failure.

The field of Predictive Maintenance has developed around the desire (or is it requirement?) to know when machinery is likely to fail. If you can see the future early enough, the equipment can be repaired during a scheduled downtime instead of causing a catastrophic failure at an inopportune moment. There are many different ways to monitor the conditions of equipment, but thermography is certainly one of the most popular.

Thermography provides a heat sensitive picture of an object. By comparing the results of thermographic images over time, changes in the temperature of objects can be detected and analyzed to determine if failure is likely. The nice thing about this is that most objects, whether mechanical, electrical or fluid-based, exhibit some type of heat increase before failing.

When electrical connections become dirty or corroded, they resist current, which creates heat. This heat increases the rate of corrosion, which increases the heat, until the circuit catches fire. In mechanical devices, lubrication, alignment and vibration problems create friction or require more power, both of which produce heat. Fluids also become hotter if their path is obstructed in any way.

Thermography can also detect failures in the insulating properties of materials. If the seals on your home windows are failing, this will show up as heat around these areas. A common application is called refractory analysis. Over time, the bricks that line a furnace wear down. As they do, the walls get very hot.

The earlier this heat can be detected, the earlier it can be dealt with. One company that is very strong in this area is Inframetrics, Inc. of Billerica, MA. Recently, the company introduced three new infrared camera systems that "revolutionize the business," according to Andrew Teich. These new models, the ThermaCAM PM180, PM280, and PM 380, have a number of features that Inframetrics believes separate them from other products of this type.

One key to these new cameras is that they are the size and weight of standard handheld camcorders. They even use traditional camcorder batteries to operate for over 2 hours in the field. With an optional battery belt, this time period can be extended to 12 hours.

"In the past, you needed 20 pounds of equipment (for thermal imaging)," explains Teich. With ThermaCAM, the cameras weigh less than 4 pounds. This doesn’t affect their durability, however. All three models use cast aluminum housings and can withstand very high levels of shock and vibration.

Another unique feature of these cameras is the type of sensor used for imaging. These are hand-held focal plane array radiometers. Instead of a single infrared sensor that moves around to provide an effective resolution of 100x100 pixels, the new "80 series" cameras contain a 256x256 array of IR detectors for very high resolution. The result is an image with over 65,000 measurement points compared to only 10,000 points for other cameras. "We’ve increased the resolution by over six times," comments Teich.

On the PM 280 and PM 380 models, a third key is the ability to store up to 400 images on removable 80 MB flash memory cards. Each image is stored in a proprietary, 12-bit grayscale format. Using software, these values are converted to meaningful temperatures. Normally, these temperatures range from –10 degrees Celsius to +450 degrees. The PM 380, however, can be used in environments with higher temperatures.

Once the images are taken, they are analyzed using software available from Inframetrics. Teich says "five different Windows packages are available, ranging from very basic analysis to real-time processing." Because of the proprietary nature of the image format, only Inframetrics software can be used with the cameras. The pictures cannot be loaded into third party applications and analyzed.

By itself, knowing that there is a change in temperature doesn’t tell you exactly when a failure will occur. However, that probably isn’t the most critical point. The goal is to have the time to repair the problem before it gets out of hand, and this has made thermography a very popular tool for predictive maintenance.

The ThermaCAM product line contains other models in addition to these three newest cameras. Pricing on the cameras range from $15,000 up to $60,000. The software, which is purchased separately, is priced from $2500 - $12,000.

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