Vibration analysis, also known as vibration analysis, is a diagnostic method for monitoring the operating conditions of machines and systems and provides important information about their condition. It is used to measure and analyze vibrations that occur in rotating machines during operation and to detect potential problems such as imbalances in the rotor or defective bearings at an early stage. This analysis plays a key role in maintaining the operational efficiency and safety of machines. In this context, it can prevent energy losses, quality defects and even machine failure, thereby minimizing the risk of accidents and extending the service life of machines and systems.
Vibration analysis – basics and definition
Vibration analysis is a diagnostic method for monitoring vibrations. Vibration analysis aims to monitor the vibration levels of rotating machinery and examine the patterns in the vibration signals. It is typically applied to both the time history of the vibration signal and the frequency spectrum obtained by applying the Fourier transform to the time history.
Time domain analysis, based on the chronologically recorded vibration histories, reveals when and how severe abnormal vibration events occur by extracting and examining parameters such as root mean square (RMS), standard deviation, peak amplitude, kurtosis, crest factor, skewness and several others. This analysis is able to evaluate the overall condition of the monitored machines and systems.
Analyzing the frequency spectra allows typical problems to be identified, such as imbalances in rotating parts, misalignment of shafts and drives, bearing damage, loose parts (loose screws or connections) or resonances in the natural frequency range of the machines.
What are vibrations?
Vibrations are multidimensional, so vibration testing in practice requires an understanding of various parameters. The most important parameters are amplitude, frequency and phase:
- Amplitude refers to the strength of the vibration and is usually measured in units such as displacement (micrometers), velocity (inches per second or millimeters per second) or acceleration (g).
- The frequency measures the number of vibrations per unit of time and is normally expressed in Hertz (Hz).
- The phase refers to the relative timing of the mode of vibration and is usually measured in degrees.
Critical vibrations can be reduced or even completely eliminated under certain conditions, for example by using vibration dampers as one of several effective methods.
A distinction is also made between two main types of vibration:
- Forced vibrations occur when a periodic external force or excitation is applied to a system, resulting in vibrations. Examples of this are irregularities generated by a running motor or a frequency converter.
- Natural or free vibration, also known as resonance, occurs when a system vibrates at its natural frequency. This type of vibration can be problematic if the natural frequency of the machine coincides with the operating frequency, as this can lead to excessive vibration.
How the vibration analysis works
Vibration analysis is usually divided into four principles, and each principle provides specific information about the working conditions and characteristics of the vibrating parts. Various tools and principles are used to perform the analysis in order to measure and understand the vibration behavior.
Here are the basic functions of vibration measurement:
- Time domain: In this approach, a vibration signal is recorded using a transducer that converts the vibration into an electrical signal. This signal is called a waveform and shows the amplitude of the vibration over time. The time period makes it possible to display abnormal vibrations directly on the screen, which makes some problems easier to recognize.
- Frequency domain: The waveform from the time domain is subjected to a spectral analysis to create a frequency spectrum. This spectrum shows the vibration in terms of its frequency and amplitude. Most detailed analyses of machine vibrations are performed in the frequency domain.
- Common region: Since vibration signals vary over time, it is sometimes helpful to calculate several spectra simultaneously. The Gabor-Wigner wavelet technique makes this possible and is used to create variants of the fast Fourier transform (a mathematical method for analyzing the frequency of signals).
- Modal analysis: Modal analysis uses measured frequency response functions of a machine part to create a computer model. This model shows the different vibration modes and can be customized to investigate the effects of changes such as mass or stiffness.
In addition to these basic principles, there are other analysis methods, calculations and algorithms that are used to determine various aspects of vibration analysis. These include the time waveform, Fast Fourier Transform (FFT), phase measurements, order analysis, power density spectrum (PSD), envelope analysis, orbit analysis and resonance analysis. Based on these results, a machine or system can be optimized in terms of vibrations.
In addition to analyzing vibrations, other measurements can also be carried out, such as temperature, power or pressure measurements.
What is an FFT oscillation analysis?
FFT vibration analysis (Fast Fourier Transform vibration analysis) is a technique for analyzing vibrations in mechanical systems. This analysis method uses the Fast Fourier Transform (FFT) to convert vibration signals recorded in the time domain into the frequency domain. FFT vibration analysis allows vibration signals to be broken down into their individual frequency components. This enables a detailed examination of the different frequencies contained in a vibration signal.
The fast Fourier transformation generally requires fewer arithmetic operations than the conventional Fourier transformation with the same results.
FFT vibration analysis is often used in machine diagnostics and condition monitoring to identify problems such as imbalances, bearing defects, misalignments and other machine faults. It provides valuable information for the diagnosis of mechanical problems and enables targeted measures to be taken for the maintenance and repair of machines.
What is a modal analysis?
Modal analysis is a method for investigating the structural dynamics of objects, including their vibration behavior and resistance to external forces. It is used to test, optimize and validate designs. Modal analysis is used to calculate the natural resonance frequencies of objects and damping parameters.
In addition, the eigenmodes, which represent the vibration behaviour of the objects, can be visualized on animated geometric 3D models. These modal parameters, which include natural frequency, modal damping and mode shape, are referred to as modal models.
In order to create accurate modal models, thorough modal analyses must be performed based on precise measurements, a process often referred to as experimental modal analysis.
Cause of vibrations in systems and machines
Vibrations in systems and machines can have various causes, including
- Imbalance: An unbalanced weight in a rotating component generates centrifugal forces and causes vibrations. This can be caused by manufacturing defects or maintenance problems.
- Misalignment / shaft imbalance: If machine shafts are not correctly aligned, vibrations will occur. This can occur during assembly or over time.
- Wear: Worn components such as bearings, drive belts or gear wheels can cause vibrations.
- Inadequate fastening: Loose bearings or components that are not properly fastened can increase vibrations and cause damage.
These vibrations can lead to premature wear, energy loss, unplanned downtime and safety issues. Proper measurement and analysis are crucial to prevent such problems and enable preventive maintenance. Serafima is happy to help you in this case.
Vibration measurements
Measuring vibrations is a crucial step in assessing exposure to vibrations. This involves measuring vibration acceleration in meters per square second (m/s2) using a vibration meter. This measurement of acceleration makes it possible to quantify the strength or intensity of vibration behavior, which is important to assess potential health or functionality impacts. Thus, the measurement of acceleration can provide additional information about the speed and amplitude of the vibrations.
Equally important is the consideration of the direction in which the vibration acts, and this is measured in predefined directions. The frequency of the vibration and the duration of exposure are also determined.
Advantages of vibration analysis
- Earlier fault detection: Vibration analysis can detect developing faults in machines long before they become visible or audible to human senses. This early detection capability helps maintenance teams to plan repairs or replacements before major stresses occur or disturbing noises develop.
- Improved maintenance planning: By identifying the severity of machine faults, the analysis enables effective resource planning. This targeted approach can lead to cost optimization and improved equipment reliability.
- Reduced maintenance costs: Finding and fixing machine faults before they lead to catastrophic failures can save companies from costly repairs and equipment replacements. In addition, this maintenance based on vibration analysis extends the life of machines, reducing long-term capital expenditure.
- Improved safety: The proactive detection and elimination of potential mechanical failures significantly reduces the risk of accidents and injuries in the workplace.
- Increasing energy efficiency: Defective machines often consume more energy than usual, which leads to increased operating costs. By eliminating problems with the help of vibration analysis, the energy efficiency of the systems can be optimized.
Monitoring and vibration technology
Condition monitoring of rotating machinery enables continuous monitoring of the condition of the equipment in order to detect changes in vibration trends at an early stage and thus enable predictive maintenance. This proactive approach can prevent unplanned downtime and significantly increase plant availability. Reliable condition analysis and continuous monitoring require powerful vibration sensors, intelligent sensor technology for measuring and testing and advanced vibration analysis software.
It is particularly important to adapt the monitoring system to the specific requirements of each system, including the vibration monitoring of bearings and gears as well as the targeted identification and filtering of disruptive influences. This ensures that no potentially damaging developments are overlooked and that the machine always remains in optimum operating condition.
Serafima – Competent service on site
At Serafima, we understand the crucial role of vibration analysis in industry. We offer reliable solutions for the maintenance of your fluid and process engineering systems across all industries, ensuring safety and efficiency worldwide.
Whether you need vibration analysis, technical advice or customized solutions, our experienced team is at your side. With our unique CMaaS or RaaS – Reliability as a Service concept, we offer you the option of predictive and predictable maintenance. With over two decades of experience as a solution provider for systems and machines in various industries, we are your manufacturer-independent partner for comprehensive system protection and sustainable success. We always act in a customer-oriented, professional and highly flexible manner in order to fully meet your requirements.
Do you need help with the maintenance of your systems? Contact us today for customized solutions and first-class advice.