Investor-owned electric utilities are chartered to provide cost-effective and reliable electric service. An important element in ensuring the reliability of the electric system is a proactive preventive maintenance program. One of the tools available to identify areas of possible failure is the thermal imaging camera, which can capture an image and rapidly display areas of varying temperatures in different colors without contact. This allows for the visual determination of specific equipment elements that are operating at higher temperatures than adjacent elements. Higher operating temperatures can be an indicator of potential problems.
This article discusses planning, operation, and documentation procedures designed to effectively use the thermal imaging camera as a critical element in an effective reliability program. All thermograms included here were taken with a FLIR ThermaCAM P45 infrared camera.
Camera Setup and Operation
Prior to taking thermal images of equipment, it is important to become familiar with how to operate the camera. Once that is fully understood, attach all the required cables to the camera and turn it on. Make sure that both the camera and the viewfinder are focused, if the viewfinder has such an adjustment (Figure 1). Viewfinders are recommended for working outdoors, and external monitors are recommended when working indoors. In addition, take care to ensure that direct sunlight does not enter through the eyepiece, which would damage the video display. It is a good idea to cover the lenses with lens caps and to remove batteries from the camera when it is not in use.
1. Focus the image. A focused image is not only easier to view but it also looks more professional, and the apparent temperature will be higher when viewing a hot spot. Courtesy:City Light and Power
Once the thermal images are captured, level, distance, emissivity, and span can be changed in post-image processing. Here are some camera-setting suggestions to optimize the usefulness of your thermal imaging camera.
Pick a Color Palette. Though a number of color palettes are available in infrared cameras, experience has shown that black and white provides the best resolution for scanning and focusing. When scanning large smooth surfaces, color can help detect subtle temperature changes. It is important to note that images stored on the PCMCIA card are saved as raw data that can be analyzed and manipulated later.
Set Level and Span. Temperature span is like "Thermal Contrast." In fact, it is similar to the contrast control adjustment on television sets. Level is like "Thermal Brightness" and is similar to the brightness adjustment on television sets. This is often referred to as thermal tuning. Figure 2 shows an example of proper temperature span setting on an ammonia injector heater electrical control panel. From the thermograph it appears that one fuse is blown. Thermal imaging can also detect such things as balanced and unbalanced loads, as shown in Figures 2 and 3.
2. Confusing options. This ammonia injector heater electrical control panel appears to have a blown fuse. Courtesy: City Light and Power
3. Unbalanced load. The ammonia injector heater electrical control panel wires (L) are fiberglass-wrapped insulation and have unbalanced electrical loads (C). A infrared scan after the loads were balanced (R) showed a more even temperature spread. Courtesy: City Light and Power
Consider Distance and Temperature. It is important to consider the effect of distance on the accuracy of the thermal image captured. If the thermal image is captured from too far away, any small areas of high temperature will be difficult to detect because the lower temperature of adjacent areas is averaged along with the hot ones.
As an example, using a 150-inch to 1-inch lens will require that the image be captured at a distance of 12.5 feet for a 1-inch target (150/12). To measure a ¼-inch target, the image must be captured at a distance of 37.5 inches. Conversely, to capture the ¼-inch target from 12.5 feet away, a 4 x lens — 600-inch x 1-inch — will be required.
The following additional factors must be carefully considered to obtain good temperature measurements:
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Camera focus. Infrared radiation is a form of electromagnetic radiation that is composed of long and short wavelengths. Infrared and visible light travel at the speed of light, and can be reflected and refracted. When the image is out of focus, the accuracy of the detected temperature is negatively impacted and data are lost.
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Temperature range. Temperature range is important because out-of-range data cannot be recovered.
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Operating distance. Operating distance is important in considering spot size ratio.
Just remember FoRD (Focus, Range, Distance) when you are setting up your camera, and you’ll get accurate temperature measurements.
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