Vibration analysis techniques

We were discussing common faults we detect by vibration analysis and steps for conducting vibration analysis in our previous posts. Let us see here vibration analysis techniques in this post.

Vibration analysis is a technique that is used to measure, analyze and diagnose the behavior of mechanical systems in response to vibration. This technique involves measuring the vibration signals from the mechanical system and analyzing the data to identify the root cause of the vibration.

The technique of vibration analysis can be used in a wide range of industries, including aerospace, automotive, power generation, manufacturing, and many others. It is used to identify and diagnose a variety of mechanical problems such as unbalanced rotors, misaligned shafts, bearing wear, resonance, and other issues that can cause unwanted vibration in machinery.

The vibration analysis technique involves several steps, including data acquisition, signal processing, data analysis, and interpretation. Vibration measurement is typically done using accelerometers or other vibration sensors that are placed on the equipment. The measured data is then processed and analyzed using software tools to extract useful information.

The analysis techniques used in vibration analysis can include time-domain analysis, frequency-domain analysis, phase analysis, modal analysis, and order analysis. The results of the analysis are interpreted to determine the root cause of the vibration and to recommend appropriate corrective actions.

Time domain vibration analysis technique

Time domain vibration analysis is a technique used to analyze and interpret vibration signals in the time domain. This approach involves analyzing the raw vibration data collected from sensors over time to detect any changes in the vibration patterns or characteristics.

The primary advantage of time domain analysis is that it provides a detailed view of the dynamic behavior of the system over time, allowing for the detection of both transient and steady-state vibrations.

Let us see here now the time domain vibration analysis steps as mentioned below

Data acquisition: The first step is to acquire the vibration data from sensors installed on the system. This data can be collected using accelerometers, velocity transducers, or displacement transducers.

Data pre-processing: The second step is to preprocess the raw vibration data to remove any noise, drift, or bias. This step may involve filtering, averaging, or resampling the data to improve its quality and accuracy.

Time waveform analysis: The third step is to perform time waveform analysis to visualize the vibration data in the time domain. The time waveform is a graphical representation of the vibration signal over time and can reveal changes in the amplitude, frequency, or phase of the vibration signal.

Peak analysis: The fourth step is to analyze the peaks in the time waveform to detect any abnormal vibration behavior. This may involve identifying peak amplitudes, peak frequencies, or peak-to-peak displacements. The peak analysis can provide information about the severity and location of the vibration problem.

Trend analysis: The fifth step is to perform trend analysis to track the changes in the vibration patterns over time. This may involve plotting the vibration data over time and analyzing the trends using statistical methods.

Diagnosis: The final step is to diagnose the root cause of the vibration problem based on the time domain analysis results. This may involve correlating the vibration data with other diagnostic data such as temperature, lubrication, or visual inspection.

Frequency domain analysis technique

Frequency domain analysis is a common technique used in vibration analysis to analyze the frequency components of a vibration signal. This analysis involves converting the time-domain vibration signal into the frequency-domain using a mathematical process called Fourier transformation.

The frequency-domain analysis provides valuable information about the frequency components that make up the vibration signal. The amplitude and phase of each frequency component can be determined from the frequency spectrum, and this information can be used to identify the sources of the vibration.

The frequency-domain analysis is typically performed using a spectrum analyzer, which displays the frequency spectrum of the vibration signal. The spectrum analyzer shows the amplitude of each frequency component on a logarithmic scale, allowing the analyst to identify the dominant frequency components that are contributing to the vibration.

One of the main advantages of frequency-domain analysis is that it can identify the natural frequencies of a mechanical system. These natural frequencies can be important because if a machine is operating at or near its natural frequency, it can result in excessive vibration and potential damage to the machine.

Another advantage of frequency-domain analysis is that it can identify the frequency components that are related to specific machine components, such as bearings, gears, or shafts. By identifying the specific frequency components that are related to a particular component, engineers can diagnose the source of the vibration and determine the appropriate corrective action.

Phase analysis technique

Phase analysis is a vibration analysis technique used to determine the phase relationship between two or more vibration signals. This approach involves comparing the phase angles of the signals to detect any changes or anomalies that may indicate a fault or defect in the system. The phase analysis technique can detect problems such as misalignment, unbalance, or looseness.

Let us see here now the phase analysis technique as mentioned below

Phase analysis: The third step is to perform phase analysis to compare the phase relationship between two or more vibration signals. This involves calculating the phase angle of each signal relative to a reference signal and comparing the phase differences between the signals.

Phase plot: The fourth step is to plot the phase angle data as a function of frequency to visualize the phase differences between the signals. This plot can reveal any changes in the phase relationship between the signals that may indicate a fault or defect.

Diagnosis: The final step is to diagnose the root cause of the vibration problem based on the phase analysis results. This may involve correlating the phase angle data with other diagnostic data such as temperature, lubrication, or visual inspection.

Modal analysis technique

Modal analysis is a vibration analysis technique used to determine the natural frequencies, damping ratios, and mode shapes of a structure or mechanical system. This technique involves exciting the system with a known input and measuring the resulting vibration response at different points on the structure.

Modal analysis is used to understand the dynamic behavior of structures and mechanical systems, and it can help identify and diagnose vibration problems.

Let us see here now the modal analysis technique as mentioned below

Excitation: The first step is to excite the system with a known input such as a hammer blow or a shaker. The input should be strong enough to excite all the modes of the system.

Data acquisition: The second step is to measure the resulting vibration response at different points on the structure. This data can be collected using accelerometers or other vibration sensors.

Data processing: The third step is to preprocess the raw vibration data to remove any noise, drift, or bias. This step may involve filtering, averaging, or resampling the data to improve its quality and accuracy.

Modal analysis: The fourth step is to perform modal analysis to determine the natural frequencies, damping ratios, and mode shapes of the system. This involves calculating the frequency response functions (FRFs) of the system and using these to identify the natural frequencies and mode shapes.

Mode shapes: The fifth step is to visualize the mode shapes of the system. Mode shapes are the shapes that the system vibrates in at each of its natural frequencies, and they can be visualized using animation or other graphical methods.

Diagnosis: The final step is to diagnose any vibration problems based on the modal analysis results. This may involve comparing the natural frequencies and mode shapes of the system to those of a healthy system, or correlating the modal analysis results with other diagnostic data such as temperature, lubrication, or visual inspection.

Order analysis technique

Order analysis is a frequency domain analysis technique used in vibration analysis to analyze the vibration signals of rotating machinery. In rotating machinery, the vibration signals typically have a periodic nature due to the rotation of the machine components. Order analysis is used to separate the vibration signals into their rotational components or orders.

The order analysis technique involves synchronizing the vibration signals with the rotation of the machine, so that the vibration signals are aligned with their corresponding orders. The orders are typically defined as multiples of the rotational frequency or the frequency of a specific component of the machine, such as a gear or a blade passing frequency.

Once the vibration signals have been synchronized with their corresponding orders, the frequency spectrum of each order can be analyzed separately. This analysis can provide valuable information about the sources of vibration and their relationship to the rotation of the machine components.

Order analysis is particularly useful in diagnosing faults in rotating machinery such as pumps, motors, and turbines. The technique can help identify specific components that are causing excessive vibration and allow engineers to take corrective action before serious damage occurs.

One of the key benefits of order analysis is that it can help distinguish between different sources of vibration. For example, if there is a bearing fault, the vibration signals will typically be concentrated at the gear mesh frequency and its harmonics. However, if there is an imbalance, the vibration signals will be present at all orders.

Spectral analysis technique

Spectral analysis is a common technique used in vibration analysis to analyze the frequency content of a vibration signal. Spectral analysis involves converting the time-domain vibration signal into the frequency-domain using a mathematical process called Fourier transformation.

The result of the Fourier transformation is a frequency spectrum that shows the amplitude and phase of each frequency component that makes up the vibration signal. The frequency spectrum is typically displayed using a graph with frequency on the horizontal axis and amplitude on the vertical axis.

Spectral analysis can provide valuable information about the frequency content of a vibration signal. By analyzing the frequency spectrum, engineers can identify the dominant frequency components that are contributing to the vibration and determine the appropriate corrective actions to reduce or eliminate the vibration.

Spectral analysis can be performed using the following mentioned methods.

Fast Fourier Transform (FFT): This is the most common method of spectral analysis used in vibration analysis. FFT is a fast algorithm used to compute the discrete Fourier transform of a sequence, which is then used to calculate the frequency spectrum.

Welch method: This method involves dividing the time-domain signal into overlapping segments, and then computing the power spectrum for each segment. The power spectra for each segment are then averaged to obtain a more accurate frequency spectrum.

Periodogram method: This method involves computing the power spectrum of a time-domain signal using a non-parametric approach. The periodogram method is simple and easy to use, but it can produce noisy results.

These vibration analysis techniques are valuable tools for diagnosing and troubleshooting problems in mechanical systems and ensuring their reliable and efficient operation.

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What are the parameters of vibration analysis?

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