Vibration Analysis

Vibration analysis is used in the context of maintenance to check rotating parts for possible faults such as defective bearings or imbalances. In vibration analysis, the vibrations emitted by rotating parts are detected and recorded by special technical equipment. In a subsequent analysis, the vibration amplitudes and vibration patterns allow conclusions to be drawn about the condition of the rotating components and the corresponding bearings. If deviations from the target condition are detected, the vibration analysis allows necessary repairs to be identified at an early stage and taken care of before the machine breaks down. The downtimes that are always required for a repair can thus be reduced on the one hand and shifted to times outside of production on the other.

Causes for vibrations on machines or systems with rotating components can be of the most varied nature. Common sources of faults include:

• Imbalances and alignment errors
• Deposits on fans
• Toothing errors in gearboxes
• Curvatures of shafts
• Occurring vibrations caused by fluids
• Problems in the foundation or with defective erection elements

Excessive vibrations on rotating machines, systems or generators not only produce uneven running and high noise levels, but also place stress on all components. Bearings in particular suffer from increased loads. Vibration fractures can occur, possibly resulting in lengthy repair work.

The larger and more complex a rotating machine is, the more critical vibrations are during operation. If the occurring vibration amplitudes exceed a maximum value, most severe and expensive defects with long downtimes are to be expected. To prevent these faults, DIN ISO 10816 (new designation 20816) or API 670 has defined requirements for protection systems used. The systems monitor, among other things, the absolute bearing vibration by means of acceleration sensors or a relative displacement vibration or axial shaft movements by means of non-contact displacement sensors.

In order for a vibration analysis to take place, the so-called phase positions of a vibration must first be recorded. For this purpose, reference sensors are usually used which detect the position of the rotating parts to be monitored (shafts or similar) and simultaneously measure the speed. The reference values obtained can then be used to monitor characteristic values that allow the vibration occurring to be evaluated. These characteristic values include

• Vibration amplitudes
• Vibration width
• Harmonic vibration components

In conventional predictive maintenance, machines and systems are shut down or switched off at regular intervals to check components for possible wear or defects. In the process, components that are actually still functional are regularly replaced. This produces unnecessary and at the same time expensive costs. On the other hand, some damage is detected much too late or not at all during conventional maintenance.

In the course of Industry 4.0, conventional maintenance is increasingly being replaced by a predictive variant known as condition monitoring. In condition monitoring, machines or systems are continuously monitored by sensors. Deviations from the ideal target state are detected by digital systems at an early stage and can subsequently be eliminated in a timely manner before defects even occur. Vibration analysis is indispensable in the context of modern condition monitoring. Since even the smallest deviations in the phase positions of a vibration can indicate a fault, vibration analysis reliably protects against serious damage and expensive production downtimes.

The use of vibration analysis sensors and the necessary software results in not inconsiderable initial acquisition costs. The expertise required to evaluate the data is also a disadvantage in times of a shortage of skilled workers. However, the costs are quickly put into perspective when compared directly with the costs incurred in the event of a machine or system failure.