What is vibration?
In order to better understand what vibration analysis is, let’s first find out what vibration is?
In technical terms, vibrations are mechanical oscillations that respond to forces pushing objects outside their equilibrium or resting point. These highs and lows, or back and forth swings, are measurable. They relate in terms like frequency, waveforms, and spectrums. Vibrations respond directly to timed intervals that can be measured using suitable product vibration testing equipment.
Vibrations can be periodic with specific wave intervals, like pendulums in mechanical clocks. Or they can be random, such as vehicle suspensions responding to a rough gravel road. Vibrations can also happen to static devices like electronic equipment sitting on a shelf where external forces cause them to shake. They can also occur in mobile equipment such as engines and fans that produce internal forces, causing them to vibrate.
Many mechanical vibrations are desirable outcomes of planned design. Loudspeakers are good examples where vibrations are intentional to produce sound. However, some vibrations are undesirable and result from improper design or fair wear and tear on equipment out of balance or improperly tuned.
Whether vibrations are intentional or unintentional, there are precise vibration testing and analysing services and vibration testing standards available to verify parameters. These vibration testing facilities can determine whether oscillations are inside or out of tolerable range.
What is Vibration Analysis and what is it used for?
Vibration analysis is the most prevalent method used to monitor the levels and patterns of vibration signals within a component, machinery or structure, in order to detect abnormal vibration events and then using that information to analyse and evaluate the overall condition of the component, machinery or structure.
In short, vibration analysis helps you monitor and detect issues using vibration data. Vibration analysers separate vibration signals into amplitude and frequency components, using Fast Fourier transform algorithms, to ease failure recognition.
By extracting and studying parameters such as root-mean-square (RMS), standard deviation, peak amplitude, kurtosis, crest factor, skewness and many others, the time domain analysis, on chronologically recorded vibration waveforms, reveals when and how severe the abnormal vibration events occur. Time domain analysis is able of evaluating the overall condition of the targets being monitored.
In real world applications, particularly in rotating machinery, in addition to time domain analysis, it is highly desirable to incorporate the frequency spectrum analysis. It is difficult to use only time waveforms to examine the condition of the critical components such as gears, bearings and shafts in a large and complex rotating equipment, because will generate a mixture of vibrations, which is a combination of vibrations from each rotating components. In this case, frequency analysis decomposes time waveforms and describes the repetitiveness of vibration patterns, so that the frequency components corresponding to each components can be investigated. In addition, the Fast Fourier Transform (FFT) technique facilitates fast and efficient frequency analysis, as well as the design of various digital noise filters.
Vibration analysis it is a non-invasive method as such it does not require you to disassemble or stop the machine. In fact, the principle of a vibration analyser is a sensor transforming movement into an electric signal and then the analyser calculates all predefined parameters and then stores this signal.
How Do You Measure Vibration?
Whereas the procedures and formulas used to calculate various forms of vibration can get complicated, it all starts with using an accelerometer to measure vibration. Based on different types of vibrations, there are accelerometers designed to measure displacement, velocity and acceleration, with different measuring technologies, such as piezoelectric (PZT) sensors, microelectromechanical sensors (MEMS), proximity probes, laser Doppler vibrometer and many others.
Anytime a component, machinery or structure is running, it is making vibrations. An accelerometer attached to the equipment generates a voltage signal that corresponds to the amount of vibration and the frequency of vibration the machine is producing, usually how many times per second or minute the vibration occurs.
To ensure that high quality data is recorded, the accelerometer installation is critical. The recommended method for installing accelerometers is to stud mount the accelerometer on a flat and clean surface on the machine. This ensures that a broad and smooth frequency spectrum is captured. When stud mount is not applicable, magnet holders, wax or glue can be adopted as substitutions with vibration levels and frequencies considered.
What Can Vibration Analysis Detect?
Vibration analysis is capable of identifying almost all the faults that a component, machinery or structure can have.
Time domain vibration analysis is able to monitor vibration levels. Limits of acceptable operation vibration can be pre-defined either through long-term operation and maintenance history or through referring to established standards. If the limit is breached, this could be that the overall health condition of the component, machinery or structure is deteriorating and defects have developed.
Frequency domain vibration analysis helps detect abnormal vibrating patterns. For example, a crack that has developed on a roller bearing outer race will lead to periodic collisions with bearing rollers. In time waveform, this information is usually hidden and masked by the vibration from other sources but by studying the frequency spectrum, the periodicity of the collisions can be discovered and consequently detect the presence of bearing faults.
All data collected from the accelerometer goes directly into a data collector (software), which records the signal as either time waveform (amplitude vs. time), or fast Fourier transform (amplitude vs. frequency), or both. All of this data is analysed by computer program algorithms, which in turn is analysed by engineers or trained vibration analysts to determine the health of the machine and identify possible impending problems like looseness, unbalance, misalignment, lubrication issues and more. The following are the most common faults that vibration analysis identifies:
Resonance and natural frequencies
Misalignment
Imbalance
Bearing failures
Mechanical looseness
Electrical motor faults
Critical speeds
Bent shafts
Gearbox failures
Empty space or bubbles in pumps
ETS Solutions Asia - Vibration Training/Course
Finding a Vibration Analysis Equipment
Find the best vibration analysis equipment that matches your needs.
Want to learn more about vibration analysis, join our training courses.
ETS Solutions offers basic and advanced training courses designed for engineers and technicians new to the subjects as vibration testing, durability testing, acoustic measurement, and also offering a useful refresher course for more experienced users.
