Uptime Magazine - October/November 2008 - (Page 64)

ment that was digital, on which you simply took the contact probe, touched a bearing and got a db reading and a fairly good sound to go by. No fancy firmware, trending or waveform analysis software. Figure 4 - Trending bearings and motors over time paints a clear picture of their health, making an accurate diagnosis easier. bad that, even if you took the headphones off, you could hear it easily. That’s a bearing in a catastrophic failure condition. No problem, get it out of there. But, you will be much more accurate in your diagnoses if you stick with the baseline and trend method. To Go Where No Man Has Gone Before Maybe its time to pay a little more attention to this metaphor. Here we are in the age of technology, where the world seems so Star Trek like. The world of technology is advancing at such an incredible rate. Take the newest “Batman” movie, where, after his cape instantly becomes rigid to form the shape of a batwing, Batman glides through the air to a soft landing. Far out, you say. Scientists tell us that this technology is not limited to the Caped Crusader. It’s actually here now, just not on a batwing glider. I recently watched an interview with a scientist about the batwing glider. He confirmed that there are compounds/materials recently discovered, that “when the molecules are subjected to magnets or some other energy field, the molecules sort of “get in line” so to speak to form a rigid material”. Although this memory type compound is not advanced enough to allow a cape to instantly form into a batwing glider, it can’t be too far off. To think not too long ago my forefathers communicated with smoke signals. And today, much like Star Trek and Batman, we can choose to wear a little device in our ear to communicate with each other. So, what does this have to do with airborne ultrasound? That’s just it, nothing. Where are the ultrasonic advancements in predic- fore any other indicators such as heat or vibration. Increased friction and impact creates changes in ultrasonic signatures as the bearing condition moves towards failure. As impact is occurring certain bearing components may vibrate or ring. This sound or noise that the bearing makes is observed in the ultrasonic frequency range as an increase in amplitude”. By its very nature, ultrasound, is “analog”, meaning that if you receive a signal and send it to a meter (non-digital) such as a ballistic meter, it is an analog signal. Personally, I liked the sound of an analog unit. For the first 10 years of my career, my ears were trained using an analog unit. I found the sound that I was hearing more realistic, more of what I, as a technician, could relate to. Think of it as the difference in listening to music on a vinyl LP and a CD. The vinyl actually has a much warmer, richer sound than the CD. So what happened? The digital age came upon us. Suddenly, if your instrument was analog, it was considered an antique. Early in the digital revolution, I remember one instru- Today’s instruments have more advanced firmware and associated software. The newer units also allow us to send data to a hard drive on a computer and play it in time series or perform waveform analysis on a bearing or gearbox using a program supplied by the manufacturer (Figure 6). However, even today, ultrasonic inspection of bearings is still performed by creating a baseline first, then trending the bearing over time to watch for a significant rise in decibels to determine condition. The difference is that none of the manufacturers will give you the decibel ranges for bad bearings anymore. You and/or your reliability engineers will need to form your own modes of failure. This can only be achieved by trending your data over time to find that magic number which works for you and your facility. For years, I trained myself in listening to bearings so I could sell instruments. After 3 to 4 years of listening to bearings day-in and day-out, I think I was, and still am, pretty good at it. But in my classes today, I do not teach my students to simply walk-up, listen to a bearing and diagnose whether a bearing is good or bad. It takes a lot of time to build that kind of confidence and familiarity with the ultrasonic instrument. The exception is with a bearing that is so Figure 5 -Good clear data display is essential to understanding condition of bearings. Figure 6 - Time Series and/or Waveform Analysis software, like the Spectralyzer v1.11 from UE Systems, is available today from the manufacturers. october/november 2008 64 24

Table of Contents Feed for the Digital Edition of Uptime Magazine - October/November 2008

Uptime Magazine - October/November 2008 Contents Upfront Upclose: An Asset Management Oasis in the Desert Information Technology: Streamlining Through Simplicity Lubrication: Phases for Framing a Solid Foundation Infrared: Do Your Homework Before You Buy Maintenance Management: Get It Together by Getting Together Motor Testing: Key Elements in Motor Decision Making Precision Maintenance: Shedding Some Light on Tolerances Reliability: RCM & the Mortgage Meltdown Ultrasound: A Multidimensional Tool Vibration: The Whirling Pump Mystery, Solved with ODS Upgrade: Are You Looking in the Right Place for Your Wear Debris?

Uptime Magazine - October/November 2008

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