The its Entek Emonitor Odyssey machinery information system from Rockwell Automation integrates signals to return machine diagnostic information. Here, a system’s fatiguing vibrations make the Lissajous figure far from ideal.

Vibration is that repeating switch from kinetic to potential energy resulting from pushing, stretching, or suspension. Because it’s so often observed as waves through matter, it’s also the most convenient means of communication around. But what do vibrations have to say? It’s easy enough to understand another person speaking, because we’re wired to process words. For vibrationally complex working industrial machines, it’s impossible to interpret signals with perfect accuracy. They way systems vibrate depends on complex mass, damping, and energy propagation properties. But with a few reasonable assumptions, sophisticated materials effectively damp, and new software and measurement equipment allow analysis of critical vibrations.

A real world, empirical approach is increasingly effective insurance against machinery wear and failure caused by vibrations. In fact, more plants are making vibration analysis standard protocol so that machinery runs safely and efficiently between maintenance times. For a better picture of plant machinery health, vibration, speed, and other condition indicators are increasingly integrated into a common database. In addition to including this integration capability in their diagnostic system, Rockwell Automation, Milwaukee, Wis., has recently improved their information system to sift out error data points. This equates to fewer false alarms and more accurate maintenance calls. The Microsoft Windowsbased software system is also compatible with portable data collectors, which have becoming increasingly popular since their introduction in the 1980s. As an economical monitoring alternative, National Electrical Carbon Products, Inc., Greenville, S.C., has developed one such portable FFT vibration analyzer that displays frequency and time wave form information on the unit’s screen as a technician makes measurements. The unit includes spectral analysis software to help grade overall machine condition picked up by the unit’s dual accelerometers.

Results are compared to automatically generated spectral alarm bands based on a reference guide called The Proven Method. Created by Technical Associates, a vibration analysis teaching and consulting firm founded in Charlotte, N.C., The Proven Method is a 70-page compilation of hundreds of machine types and their corresponding application formulas. The formulas define how to apply six different band alarms across one frequency range; each band is focused on a certain machine problem (such as alignment, imbalance, or looseness). Jay Gensheimer at National explains, “Data for very specific types of machines provides an advantage when compared to the ISO standards which are acceptable, but very general, and watered down. It’s sort of like driving across country with a GPS system in your car versus without one. You gain a lot more confidence about what you’re doing right off the bat.”

Teaming up with International Source Index, Inc., Williamsville, N.Y., National also loads premium units with data software that includes fault frequencies for more than 120,000 bearings. Besides indicating when something is damaged, the software can also listen to an unidentified bearing’s frequencies, and return a list of possible manufacturers.

The Ascent vb Series vibration analyzer from National Electrical Carbon Products, Inc. is designed to be intuitive.

Another route is to continually monitor a system for vibration changes. Because noise usually has many sources and is masked by structure-borne or amplified vibrations, isolating and investigating it is difficult. Reproducing noise in a laboratory is even more challenging. To bypass these difficulties, Intonix Corp., Roseville, Minn., has developed an acoustic machinery monitor that activates alarms when constantly monitored sounds begin to deviate from their norm. Using 96 frequency bands, it learns what a system or process sounds like, then continually compares records to present signals. Used on motors, fans, and gearboxes, the monitor provides another economical alternative to direct vibration monitoring. Although its output results are qualitative, not quantitative, the mountable spectrum analyzer does help keep personnel out of potentially dangerous locations. Senior product engineer James Radmonski explains, “The sounds coming from equipment and processes in a plant are not just noise. They contain information — information that can be used to prevent breakdowns and mishaps that damage expensive equipment, cause costly loss of production, start fires, and even injure or kill workers.”

Quiet, please

Besides transmitting waves through the system, vibrating machine surfaces radiate pressure waves into adjoining air as sound. When these noises distract or even injure personnel, and when monitoring, tracking, and analyzing a system’s vibrations is of little diagnostic value, the best action is to damp it. In air, all sound frequencies travel easily, at a set speed. But inserting a soft material such as foam rubber or carpeting helps destroy sound’s pressure fluctuations. Wave energy is spent deforming the materials, and converted into thermal energy.

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