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Condition Monitoring and Predictive Maintenance

If you are using an ultrasonic sensor for leak detection and not achieving the expected results, there are better tools available. If your ultrasonic sensor is used for leak detection only, then you are not fully benefiting from the technology. Ultrasonic leak detection is recommended by many, such as the U.S. Department of Energy1, as the best method for detecting the location of leaks in order to minimize energy waste and improve plant efficiency. Ultrasonic sensors designed with the right technology and software can be used for condition monitoring and predictive maintenance. This will minimize production downtime, improve quality control and safety, and decrease man-hours by improving troubleshooting capabilities.

Consider the following summary from a third party evaluation team for the integration of ultrasonic technology in a single organization with over 500 sites:

More than 100 applications were identified in use for various equipment at each site such as boilers, heat exchangers, compressors, motors, pumps, valves, and steam traps

The total savings for the organization would be approximately $3.7 million annually

The return on investment for the integration of ultrasound with this cost avoidance would be approximately 15:1.

The return on investment for the integration of ultrasound with this cost avoidance would be approximately 15:1.

Proper integration for the proposed implementation of ultrasonic technology at this organization and other similar organizations realize the estimated benefits and more. Many companies, however, have good intentions of implementing predictive maintenance programs to decrease production and operation costs, but they lack the tools and time to develop an effective plan. This paper shall discuss ways to use ultrasonic technology for a fast and effective return on investment.

Condition Monitoring

Condition monitoring and predictive maintenance has traditionally been performed through vibration analysis, infrared, and other technologies. Ultrasonic technology is often ignored but is an excellent option, especially for organizations with lower budgets. Ultrasonic detectors are capable of accurately interpreting the sounds created by under lubrication,

over lubrication, and early signs of wear. The right ultrasonic 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 an ultrasonic receiver whose microphone can be placed in contact with the housing.

If the bearing is over-lubricated, very little ultrasound can be heard through the headset. If the bearing is under-lubricated, the intensity of the bearing will increase dramatically and other sounds may be produced 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 ultrasonic wave will produce large spikes in the signal caused by flat spots or scratches on the race. The spikes are heard as pops or crackles through the headset. 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.

When using an ultrasonic sensor 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 audible sound that is detectable by vibration sensors, but ultrasonic vibrations in steel can still interfere with the component under test if the sensitivity is adjusted too high.

You may record the settings of the sensor 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 ultrasonic 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. A decibel reading, for example, is a logarithmic unit used to describe a ratio that could include power, sound pressure, voltage, intensity, or several other factors.

The use of ultrasound technology for condition monitoring does not need to be complex, however. Software may be used to record the output of the ultrasonic sensor. Once a baseline or benchmark signal of a component is recorded, future recordings may be compared to it in order to determine the wear or proper lubrication of the component over time.

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