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34 D Thermography In Maintenance - Camera & Software Choice Dmitri Ishchenko (Australia) Applied Infrared Sensing espite the fact that thermography has been used for facility maintenance for more than 30 years and its benefits are well known, it has become a common maintenance tool only in recent years. Technology advances made thermal imaging cameras more a ff o rdable for individual companies and consultants, regular thermal imaging is now a standard maintenance and condition monitoring procedure for electrical installations. Choosing a thermal imaging system can be a daunting task considering that there are dozens of models available from numerous manufacturers and the software now plays a far greater role in image processing and report writing than before. The market offers anything from “entry level” thermal imaging cameras for as little as Aus$6,000 and up to hair-razing Aus$90,000. (Aus $1.75 equals USA $1.00) However, that task can be simplified if a prospective user focuses on a few technical parameters important for his or her task and on general user-friendliness and performance of the camera and software package. Here is what the sales professionals know but not always explain to you: Optical resolution is the single most important factor which leads to many temperature measurement errors. In simple terms, a camera with low optical resolution must be kept very close to the inspected item to measure accurately. Experienced therm o g r a p h e r s recommend having a square of at least 3 x 3 pixels “within” the tested item. This can be a difficult or impossible task for some lowresolution cameras. Figure 1 - Thermography Zoomed Screenshot
Figure 2 - Thermography Software Screenshot When this rule is not observed there is a risk of reading lower a temperature than it actually is. Such risk increases if an operator can fit only 2 x 2 pixels and it grows substantially if only one pixel reads the temperature. Optical resolution is measured in “mrad” and it depends on the number of pixels in the detector and camera lens. Good maintenance cameras are based on uncooled microbolometric detectors of 320 x 240 pixel size. They should be able to achieve about 1.6 to 1.4 mrad, which means that a projection of one calibrated pixel at 1m is a square with 1.6mm side. (note: figures such as 2.8 mrad mean lower resolution, not higher). Smaller detectors produce lower quality images even if the camera interpolates the output to the standard 320 x 240 size. (note: look out for the word “interpolated” in the camera specifications). Accuracy. Today, credible manufacturers offer accuracy of +-2 degrees or +- 2 % for maintenance applications. Typically, the high quality cameras may be more accurate but the specifications usually do not reflect that for many reasons. Claims of +- 1 degree accuracy should be met with caution. Thermal resolution or sensitivity. This parameter together with the optical resolution is responsible for image quality. Most good cameras based on 320 x 240 detector offer thermal resolution (not accuracy!) better than 0.08˚C which is enough to create a nice and sharp thermal image. Camera and software user-friendliness. This is a difficult question since people have their own “like” and “dislike” perceptions. However, for many people a rotating display (camcorder-like) is much more convenient than a built-in one and certainly better than no display at all. A larger display is generally more convenient than a smaller one. Camera controls and shortcut buttons for common functions are more convenient when they are on the display. Many hardware buttons on the camera may be confusing, on the other hand, double or triple button functioning may be annoying. Te m p e r a t u re ranges. Specifications rarely show how many sub-ranges a camera has in, say, - 20 to 300˚C or - 20 to 500˚C measurement range. Having less sub-ranges is more convenient, having more sub-ranges would require more frequent switching between them and sometimes results in difficult to understand images showing a hot spot on black background. Or a good background shot with white hot area with unreadable temperature. Manual focusing or automatic focusing. Manual generally works better in the industrial environment and lens ring focusing is quicker and easier than joystick focusing. Interesting to note that now top of the range camcorders also come with lens ring manual focusing. S o f t w a re should be stable, have enough measurement functions and, most important, provide a very good automated re p o rt writing ability. This part is often neglected when choosing a system package but the report writing generally may take longer time than the inspection. When you make your shortlist, remember to check the reputation and the history of the manufacturer. Most good manufacturers produce very reliable thermal imaging cameras, virtually maintenance free (lens cleaning doesn’t count) and not requiring regular calibration. Most local agents are generally capable or very simple support but all serious repairs must be done overseas as having proper repair, testing and calibration facility is too costly to maintain on a local level. Dmitri Ishchenko works for Applied Infrared Sensing specializing in supplying thermal imaging and infrared equipment. For more information please visit www.applied-infrared.com.au and choose Thermography section. 35
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Page 16 and 17: 16 In one case, a large mining comp
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Page 20 and 21: 20 P a rt of your team should inclu
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Page 24 and 25: 24 To achieve success in managing m
Page 26 and 27: 26 By undertaking an interviewing p
Page 28 and 29: 28 In additional to the above four
Page 30 and 31: 30 To allow the last two points to
Page 32 and 33: 32 Are You Familiar With ‘The Law
Page 36 and 37: 36 The Case For Integrated Service
Page 39 and 40: 40 Improving The Performance Of Chr
Page 41 and 42: 42 re c u rring. Understanding the
Page 43 and 44: 44 Step 3. Identify Effective Solut
Page 45 and 46: 46 Because most RCA’s are complet
Page 47 and 48: 48 In your early planning, remember
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Page 53 and 54: 54 The second reason this is import
Page 55 and 56: 56 Demodulation: Demodulation data
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Page 65 and 66: 66 m a i n t e n a n news c e Power
Page 67 and 68: 68 $1000 REWARD!! Root Cause Analys
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Page 71 and 72: 72 performance of actual lubricants
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Page 79 and 80: Day Two: Tuesday 25, October 2005 C
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Strategic Maintenance Congress 2005
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