Even before the maintenance crisis crashed onto the stage, Plant Services believed two truths about our favorite discipline. First, we hold that no maintenance professional can get too much education. Second, we say that cross-training in technical subjects holds no downside risk. In fact, those beliefs have been among the motivations that drive this monthly column into topics that have some rational relationship to how your maintenance department operates.
It’s well accepted that predictive maintenance is one of those best practices that can help keep your company’s market offering from morphing into an import that wreaks havoc on our international balance of trade. The two predictive technologies featured here are infrared thermography and vibration analysis. As you explore the Web citations, we hope you learn something new, and then see if it works in your current reality on the plant floor. So, join me in search of practical, zero-cost, noncommercial, registration-free resources that will help you decode the shakes and see the invisible. Remember, we search the Web so you don’t have to.
Vibratory big picture
As is the case with any predictive technology, the idea is to evaluate some measurements and, if necessary, engineer a fix. What happens between those end points is the essence of maintenance excellence. A roadmap might be useful for achieving some continuity and best practices within your operation. So, for the case for vibration, you could do worse than to shake a mouse at www.machinedyn.com/revised/training/tutorial.pdf to read “A brief tutorial on machine vibration.” It’s an article in which Victor Wowk, P.E., founder and president of Machine Dynamics Inc., Albuquerque, N.M., argues that not all vibration is bad. Afterward, his 10-page article includes a decision tree that can take you from performing vibration problem diagnostics to identifying possible remedial measures that can stop the shakes. He provides a tabulation of suggested vibration limits for electric motors, generators, fans, pumps, compressors, gearboxes, internal combustion engines and turbines. Finally, you’ll find hints for analyzing the data, tips for evaluating the conclusions, ideas for root-cause analysis and a list of some corrective measures that might work.
Scribd is the name of a company founded in 2006 by Adler, Friedman and Bernstam in San Francisco. It claims more than 20 million visitors each month and more than 17 billion words in its library, which purports to be five times the size of Wikipedia. The idea behind Scribd is that it’s a vehicle by which people can publish their own material for the benefit of the rest of us who don’t. How altruistic. An example of the relevant content you can find there is a 72-page article titled “Vibration Analysis.” The target audience is anyone concerned about vibration problems with industrial equipment. Wiggle over to www.scribd.com and enter the phrase “vibration analysis” in the search box. Look for the entry with the correct title and page count. The meat of the piece begins on page six, where the lesson starts with springs and simple harmonic motion. Some 50 pages later is where you finally get into machine vibration-monitoring and tips that can help you make the most effective use of your vibration monitor. You can print the document or read it online. But, there appears to be no way to download it anonymously.
Become an expert
The great advantage of collecting vibration waveforms digitally instead of through analog methods is that you can use digital signal processing in the form of the Fast Fourier Transform (FFT) to convert the time-domain signal you collected so easily to the frequency domain signal that you can analyze so easily. Don’t view that conversion process as some sort of black magic lying beyond the comprehension of mere mortals on the plant floor. Instead, get a copy of “The Scientist and Engineer’s Guide to Digital Signal Processing” by Steven W. Smith, Ph.D., president and founder of Spectrum San Diego. This 640-page, 34-chapter book has been available for years and has undergone several revisions. The author claims that digital signal processing is one of the most powerful technologies that will shape science and engineering in the 21st century. He explains the eight reasons you should master the technology. He even offers the software that performs the signal processing. The best part of this amazing discovery is that everything mentioned here and much more are available as free downloads at www.dspguide.com. All I can say is that you’ll be doing yourself a disservice if you don’t investigate this opportunity.
Some people have a natural talent for visualizing the effect that changing the variables has on the outcome of a particular analysis. They think in numbers. Others need something more tangible. They might need a picture to see the effect of tweaking the unknowns. That fact seems to be the impetus behind the Wolfram Demonstrations Project, an open-code resource that uses dynamic computation to illuminate mathematical concepts. Developed by Stephen Wolfram at Wolfram Research Inc., Champaign, Ill., the project features more than 3,400 demonstrations that can help you get a better grasp on the technology. For example, you might want to explore the FFT. Shake that mouse toward http://demonstrations.wolfram.com and enter “fast fourier” in the search box. Then, look for the demo titled “Frequency Spectrum of a Noisy Signal.” At this point, you’ll only be able to preview a canned demo. If you want to explore on your own, you’ll probably need to download the free Mathematica Player first. Just follow the download instructions. Don’t stop there, though. Go back to the home page and find additional relevant demos that might be useful for coaching and educating your maintenance technicians.
For the mathematical savants out there, Wolfram has another site that focuses on the numerical approach. Slide your abacus beads over to http://mathworld.wolfram.com and enter “fast fourier” in the search box. This should return about a dozen citations. The one tagged as “Fast Fourier Transform” shows the math that happens inside your vibration data-collector software. And, as above, there are plenty of additional topics you can research to learn the underlying math.
Doing it in real time
Reliable Software LLC in Seattle is a very small software company that came into being in 1996. The company’s Web site (www.relisoft.com) has at least two vibratory resources you might find interesting, if not earth-shaking. The first is a rather detailed explanation of how one generates the FFT. As the link says, it goes into the “math and physics behind the Fourier Transform.” And that’s exactly what you’ll get if you want details. The multipart article starts with a discussion of audio waves in nature and if you concentrate on the definitions, the logic and the math, by the time you get to the sixth section, you’ll know how to calculate your very own FFT. Access this tutorial through the “Science” link near the top of the page.
But, if you want to skip that hard, technical stuff in favor of being a mere appliance operator, you’d better start with the “Freeware” link. This allows you to download a copy of Frequency Analyzer software, which uses the signal from your microphone and sound card to produce an on-screen FFT in real time. Select the sampling frequency, your choice of eight-bit or 16-bit data, the transform rate and the number of points you want in each transform, and watch the monitorial fireworks. Plus, you can download the source code. Go forth and enjoy.
No more shaky belts
Our postal system has come a long way in the 255 years since Ben Franklin was named postmaster general. Moving mail now relies on evolving, revolutionary, high-tech hardware, as well as the lowly conveyor belt to get your missives and remittances across the country. If a critical conveyor starts vibrating, it attracts attention. When the U.S. Postal Service Bulk Mail Center in Cincinnati initiated a five-month project to diagnose and eliminate excessive vibration on such a conveyor drive, it was turned into a step-by-step case study that you can access online at a site owned by Info Product Sites Inc., Terre Haute, Ind. Start at www.maintenanceresources.com and enter “ezine” in the keyword search box. Of the many entries that get returned, the one you want is called “Maintenance Resources e-zine.” Load it and select the archive option. Scoot down that listing to an October 1999, entry titled, “Vibration Analysis on a Conveyor Drive Unit,” a case study by Michael S. Johnson Jr., P.E. This and the many other digital presentations would have been much more user-friendly if the graphics could be enlarged to make the smaller type more easily readable. Alas, what you sees is what you gits. Bring your reading glasses.
Adjust the camera
Any decent infrared imaging camera includes a control of some sort that is to be set in accordance with the emissivity value of the target under scrutiny. Failing to do so is said to introduce sometimes gross temperature measuring errors, which, of course, can lead to grossly incorrect decisions about things that matter. According to “Welcome to the Emissivity Trail,” a tutorial by Temperatures.com Inc., Southampton, Pa., a correct setting depends as much on the temperature difference between the target and the background as it does on target’s reflectivity and other properties. You can feel the heat of this argument at www.temperatures.com/eindex.html, where a multipart article, each section a click away from the last, awaits your inspection.
A hot textbook
The next time you get involved in a training initiative, it’s a good idea to provide some tangible material your class can use for reference when they get back to work. In that spirit, we bring you an online manual that is part of a training course on thermography put on by Land Instruments Intl., Dronfield, England. Imagine your mouse going to www.landinst.com and clicking on the “Infrared Temperature Measurement” link at the upper left side. That would bring you the opportunity to click on the “PDF Downloads” link shown in the “Quick Links” box. When that loads, you’d be able to scroll to the bottom and look for the section labeled “Training Notes,” where you’ll see four articles. Based on the titles, it appears to be a treasure trove of thermographic wisdom and lore. Looks are deceiving, though, because there’s a bit too much duplicated content among the entries. Save time by investigating “Infrared Theory Notes.” After you absorb this easy-to-read piece, use it as the basis for your own in-house training course and help us stem the rising tide of lost talent we call the maintenance crisis.
A window to the future
We appear to be living in a global greenhouse and probably should expect the cost of air-conditioning and space heating to rise, given the reality of higher energy costs and forecasted environmental warming. The greater the area of glass that isolates your plant from the environment, the greater will be your HVAC cost. The more heavily insulated your roofs and walls, the more your windows become the weak link in the HVAC chain. The scientists at Lawrence Berkeley National Laboratory in Berkeley, Calif., recognized this problem and established the Infrared Thermography Laboratory to research the thermal properties of windows and other insulated systems. You can see right through it at http://windows.lbl.gov. This is where you can view a video that demonstrates chromogenic glazings, the opacity of which can be controlled. Then, there’s software. One of the six free packages the lab offers is called WINDOW. It’s used for analyzing a window’s thermal and optical performance. If you want to research daylighting, you’ll find quite a bit of material here. Be sure to click on the lower left image (the red and green rectangular shapes) to learn about the test equipment and experiments the thermography lab performs to quantify window performance. One of the links will take you to relevant technical papers the lab published. This site might be a good place to start your literature search some day when it’s time to retrofit your fenestration. Overall, it’s a link-rich site that will provide answers for diligent people who take the time to search.
Some Web sites keep getting better every time I rediscover what they have to offer. A case in point is the maintenance management site that Sandy Dunn from Assetivity Pty Ltd. in Como, Western Australia, developed. This is probably the fourth mention he’s gotten in this column during the past 12-plus years. Each visit is a rich experience that makes it so easy to lose track of time when exploring the content he’s accumulated from so many sources. And, he has plenty of material about both of this month’s topics. Toss your boomerang at www.plant-maintenance.com and hit the highlighted link to “Maintenance Articles” on the right side. Then, drop down to “Technical Articles,” where you’ll find the key to at least 108 articles about bearings and vibration, as well as 47 about thermography. I’m at a loss regarding which are the best articles to be mentioned here, so you’ll need to decide on our own.
E-mail Executive Editor Russ Kratowicz, P.E., CMRP, at [email protected].