Bearing Vibration Monitoring.. Is it Really That Simple?
Vibration & Condition monitoring is an established and necessary function to identify maintenance work and prevent costly machine downtime which in some extreme cases can run in to several thousands of pounds. To prevent nasty surprises, vibration monitoring, in whatever guise, is crucial - particularly in heavy industries such as steel or cement production, quarries and foundries.
There ae several techniques, including thermographs, amplification, ultrasound and oil analysis, but vibration monitoring is the most commonly used, but as technology advances, there now is a NEW TWIST to vibration monitoring.
The New Twist
The conventional vibration monitoring uses sensors, most commonly accelerometers, that will detect movement in a radial direction (up and down or side to side) or sometimes in an axial direction. bearings have been a major target for vibration monitoring again because of the huge costs that can be incurred with premature bearing failure.
Check out this Video below to familiarize yourself with how normal bearing monitoring works.
To get a good result, readings need to be taken directly in line with each of the bearing housings, with typically at least four measurements needed for most items of equipment, where you have two bearings in the electric motor and two bearings in the driven equipment.
It is not always possible to get a good direct 'line of sight' from the sensor to the bearing - for example, with jacketed equipment, or some duct mounted fans, and other equipment may not be accesible for taking good vibration readings - such as a long shaft or a submersible head pump (as shown below).
BUT.. There is an easy way to obtain readings in these difficult and awkward situations by using an alternative type of vibration. TORSIONAL VIBRATION is excited by a wide range of phenomena inside equipment, not just rolling element bearing faults - and it can be measured by effectively using the drive motor itself as a sensor.
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 the torque required result in variations of current relative to the voltage and this can be detected and automatically analyzed by a model based voltage & current (MBVI) system to provide a broad range of fault diagnostics and conduction monitoring.
Because a shaft is designed to transmit torque from one end to the other, the motor can pick up signals coming from the bearings anywhere along the length of the shaft.. so even with a long shaft submerged pump (like the on illustrated above), 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 characteristic frequencies.
Because MBVI systems are based on torsional signals, they can also detect signals that conventional accelerometers may not pick up so clearly - including normal journal bearing problems, vane pass rate issues, rubbing and flow turbulence. The table below shows how some phenomena - such as those affecting journal and roller element bearings - actually show up more clearly using the motor as a sensor than a conventional accelerometer.
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 saving potential to be calculated.
MBVI systems provide automatic diagnosis of faults and recommended interventions, for example with belt drives (see diagram) – these are an element particularly prone to wear, which can lead to large unnecessary vibrations elsewhere in the system and belt failure.
MBVI systems are available as fixed or portable units. Fixed units can store up to three months’ data locally, and the data can be downloaded periodically via USB, meaning that you can have continuous condition monitoring, with no need for network cabling if you choose.
And if you want to try before you buy, you can get testing done on your own machines by VANTAGE INDUSTRIAL using a portable kit, giving you a risk-free way to prove the benefit before investing in buying kit of your own.
For more information on how Vantage Industrial can help you with Bearing Vibration Monitoring just give us a call today!