How MBVI (Model-Based Voltage and Current) systems turn your motors into vibration sensors – and why this is a good idea
Vibration Monitoring is the most commonly used technique for monitoring the condition of rotating equipment, and can bring big benefits through avoiding unexpected breakdowns and enabling more efficient maintenance.
But conventional Vibration Monitoring can struggle with some situations that are getting more common in industry – with inverter-driven equipment, that brings varying speeds, varying loads, and vibration directly caused by the electrical distortions created by the inverter. And sound-proof enclosures, remote mounted or submersible equipment can all make it difficult taking a vibration reading using a conventional accelerometer. And it is not always possible to get the required direct “line of sight” from the sensor to the bearing - for example with jacketed equipment, or for some duct mounted fans.
A new way of getting vibration readings in all these difficult situations can be provided by Model-Based Voltage and Current (MBVI) Systems, that effectively turn your electric motors into vibration sensors. They detect a different type of vibration – torsional vibration – that is excited by a wide range of phenomena inside equipment, not just rolling element bearing faults. So your motor can actually tell you more about your equipment condition than conventional Vibration Monitoring.
Torsional Vibration
Whereas conventional vibration sensors measure movement of the shaft perpendicular to its axis, torsional vibration is movement of the shaft twisting along its axis. The motor driving the equipment “sees” this vibration as subtle variations in the torque required to drive the equipment. Because motor current is affected by the load on the motor, subtle variations in torque result in subtle variations of current relative to voltage, and this can be detected and automatically analysed by an MBVI system to provide a broad range of fault diagnostics and condition monitoring.
Because MBVI systems measure motor voltage and current, they can also detect electrical faults with the motor. They can also give additional information on the load on the equipment (is it being damaged by being overloaded?), its speed, the energy being consumed, and the amount of energy being wasted by developing faults, allowing energy savings potential to be calculated.
Because a shaft is designed to transmit torque from one end to the other, the motor can pick up signals coming from bearings anywhere along the length of the shaft. So even with a long shaft submerged pump like that illustrated, problems at the bottom bearing can be detected. In fact problems with any of the bearings are detected from this single measurement location. The different bearings can be discriminated by their different characteristic frequencies.
MBVI systems such as the Faraday Predictive range are available both as fixed (“S200”) or portable (“P100”) units. And because the S200 units can store up to 3 months data locally, one approach is to download it periodically via USB to a Complete Portable Workstation, which automatically builds up continuous history indefinitely. So you can get the best of both worlds: the benefits of continuous 24x7 data capture, giving you continuous history to spot when changes in trends started and better prediction of future deterioration, without the need for an IT project to connect the system to your network.
And if you want to “try before you buy” you can get testing done on your own machines by Faraday Predictive using a portable kit, giving you a risk free way to prove the benefit before investing in buying kit of your own.
This really is “a new twist” on Vibration Monitoring.
For more information visit: faradaypredictive.com
