Condition Monitoring and Predictive Maintenance

This will minimize production downtime, improve quality control and safety, and decrease man-hours by improving troubleshooting capabilities.

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Condition-Based Monitoring

Condition based monitoring and predictive maintenance has traditionally been performed through vibration analysis, shock pulse, infrared, and other technologies. Ultrasound technology is often ignored but is an excellent option, especially for organizations without the luxury of large budgets or trained, certified personnel. The CTRL UL101 ultrasound detector is capable of accurately interpreting the sounds created by under lubrication, over lubrication, and early signs of wear. The right ultrasound technology is a fast and effective means of determining such conditions in moving, mechanical components such as bearings, gearboxes, motors, compressors, etc.

Ultrasound is produced by friction, impact, turbulence, and electrical discharge. Friction and impact are the by-products of mechanical equipment. For example, a roller bearing will produce friction as the shaft and balls roll around the center. If there is too much friction, however, problems begin to occur on the production line due to imbalance, or the bearing might seize, thereby shutting down production altogether.

Proper lubrication of critical bearings is important at all times. A properly lubricated bearing will produce a smooth rolling ultrasound, detectable by the CTRL UL101 ultrasound receiver, which is placed in contact with the bearing or gearbox housing.

If the bearing is over-lubricated, very little ultrasound will be heard through the headset. If the bearing is under-lubricated, the intensity of the bearing will increase dramatically and other sounds will be inherent such as fluttering or scratchiness. Indications of an under lubricated bearing will appear in ultrasound even before infrared can detect heat increases and well in advance of vibration analysis.

In addition, once a bearing begins to wear, the ultrasound wave will produce large spikes in the signal caused by bearing defects. The spikes are heard as pops through the headset and are very noticeable relative to the normal sounds of a new, properly lubricated bearing. Once the ultrasound produced by the bearing begins to indicate these characteristics, the replacement of the bearing can be planned during normal production shutdown. The detection of wear is instantaneous. It is not necessary to take readings of the bearing from several points of contact along different axes and send the readings away for analysis.

More on Condition-Based Monitoring

When using the CTRL UL101 ultrasound detector for condition monitoring, contact the solid probe at the same point each time. Adjusting the sensitivity will minimize ambient ultrasound caused by other components. Ultrasound attenuates, or loses energy, much more rapidly than the audible sound that is detectable by vibration detectors. But ultrasound vibrations in steel or aluminum can still interfere with the component under test if the sensitivity is adjusted too high.

While establishing baselines, record the settings of the detector and component operating conditions such as speed, load, etc. Each time you monitor that component, try to maintain the same operating conditions so that changes in the ultrasound can be attributed to component wear or lubrication rather than increased speed, for example.

There is no single ultrasound characteristic that will, when considered alone, help determine the condition of a component under test. Digital indicators of relative measurements such as decibels or root mean squared (RMS) should not be solely used for trending. CTRL’s software for recording and analysis called “InCTRL Mobile” provides an RMS value for measurement of the average amplitude of sound over a 20 second interval. A value of “0” is equivalent to no sound. When recording a baseline, adjust the settings so that the RMS value indicates “10” to “50”.

Decibel is a logarithmic unit used to describe a ratio of a physical quantity such as power, sound pressure, voltage, intensity, or several other factors. Lubrication practices based solely upon a standard dB reading are, therefore, often misleading. An increase of 10 dB is insignificant if the baseline dB is 30. An increase of 10 dB is catastrophic if the baseline dB is 60.

The use of ultrasound technology for condition monitoring is not overly complex, however. InCTRL Mobile may be used to record the output of the ultrasound detector.

The recordings are uploaded to the server-side application called, “InCTRL” to establish thresholds and for future comparisons of the test point. Once a baseline or benchmark signal of a component is recorded, future recordings may be compared in order to determine the wear or proper lubrication of the component over time.

Again, signal analysis software should be easy to use and reflect the ultrasound detector’s ease of use. If the sensitivity of the detector is adjusted properly each time a recording is taken, then anomalies should be easily identifiable as the bearing begins to wear (See Fig. 3 and Fig. 4). In InCTRL, there are two types of measurement including RMS (Root Mean Square) for average amplitude and EPS (Events Per Second) for flagging of anomalies.