by Ron Sullivan and Renard Klubnik, Wilcoxon Research, Inc.
December 17, 2011

Loop powered sensors for many types of physical parameters have been around for a long time. Loop powered sensors for vibration are relatively new but are gaining widespread acceptance because they provide simple data at a fraction of the cost.

While the early vibration sensors outputted a 4-20 mA signal proportional to peak velocity, a steady stream of improvements have led to vibration sensors that output a signal proportional to root-mean-square (rms) velocity, true peak velocity, rms acceleration, peak acceleration and true peak acceleration. The latest addition is a loop powered sensor that outputs a 4-20 mA signal proportional to the peak-to-peak displacement of the monitored machine, which is equivalent to monitoring your blood pressure in millimeters of mercury or pounds per square inch. The units may be different, but the interpretation is the same. A higher or lower trend indicates further investigation is needed.

When you implement vibration monitoring with loop powered sensors, the plant receives vital, previously overlooked information. This additional knowledge provides 24/7 access to instantaneous operating information that is easy to understand, trend and alarm. Expanding your knowledge base to include pump health determined by vibration levels brings you closer to a more comprehensive health assessment and a healthy "lifestyle" for all plant equipment.

You already check and chart amperage, discharge pressure, suction pressure or even shaft rpm of your pumps. At a minimum, operating and maintenance personnel know the normal ranges and instinctively look for variations outside these ranges. Vibration is also a key indicator which can now be easily monitored in the same manner-even if you are not a vibration expert. By using cost-effective loop powered vibration sensors, a plant's existing process control system can continuously checkup on machinery and alert maintenance and reliability professionals about a pump operating outside of normal vibration levels.

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