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Vibration sensor targets low-speed applications

29 January, 2016

The British vibration monitoring specialist, Sensonics, has developed a sensor specifically designed to monitor vibrations on slow-speed machinery ­– typically rotating at less than 300 rpm. It says that traditional piezoelectric-based velocity vibration sensors are susceptible to various forms of interference in low-frequency applications that can result in spurious readings and alarms.

And, while the use of accelerometers is common on standard machinery rotating at speeds of around 1,500 rpm, these devices have limitations at lower speeds because the absolute accelerations measured are much smaller in for similar vibration displacements.

Typical problems with conventional piezo-based sensors include:

•  base strain effects caused by temperature changes, amplified by internal signal processing;

•  high-frequency and high-g vibrations caused by auxiliary machine items, that can result in transducer saturation; and

•  mains voltage interference resulting from a combination of poor local earthing and insufficient internal transducer isolation.

Sensonics' low-speed vibration sensor is said to overcome problems with other technologies

Sensonics says that its new VEL/GLF electrodynamic sensor offers superior performance to piezoelectric devices by combining high sensitivity with a frequency response down to 0.5Hz. It is designed to measure velocity vibration on equipment rotating at speeds below 300 rpm.

Due to its low-impedance electrodynamic design, the sensor is said to offer high noise immunity. It filters out high-frequency events and because no electronic integration is needed, the design is claimed to be immune from the saturation problems that can impair the reliability of piezoelectric devices.

The sensor has a standard IEPE interface for easy integration with existing plant protection and monitoring equipment.

Typical applications for the VEL/GLF are expected to be in slow-speed pumps, cooling towers, and hydroelectric and wind power generators, as well as for structural monitoring. It will help to detect the early onset of problems in rotating parts which, if left unchecked, could damage the machinery.

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