We were discussing common faults we detect by vibration analysis, steps for conducting vibration analysis and Vibration analysis techniques 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.
Vibration analysis typically involves measuring various parameters related to the motion and vibration of an object or system. Let us see some of the most commonly measured parameters in vibration analysis as mentioned here.Â
Amplitude
Amplitude is a commonly used parameter in vibration analysis to measure the severity of vibrations. In the context of vibration analysis, amplitude refers to the magnitude of the displacement, velocity or acceleration of a vibrating system.Â
There are following types of amplitude measurements used in vibration analysis.Â
Displacement Amplitude: It measures the distance a vibrating object moves from its resting position. It is usually expressed in microns or millimeters.
Velocity Amplitude: It measures the speed at which a vibrating object moves in a given direction. It is usually expressed in millimeters per second (mm/s).
Acceleration Amplitude: It measures the rate at which the velocity of a vibrating object changes. It is usually expressed in meters per second squared (m/s²) or g's (where 1 g = 9.81 m/s²).
The choice of the type of amplitude measurement depends on the characteristics of the vibration and the nature of the vibrating system being analyzed.Â
In general, higher amplitude values indicate more severe vibrations, which can lead to equipment damage, reduced efficiency, and increased wear and tear on the system. Vibration analysis can help identify the source of the vibrations and enable corrective measures to be taken to reduce or eliminate them.
Frequency
Frequency is a key parameter in vibration measurement, which refers to the number of times a vibrating object oscillates back and forth within a given period of time. In the context of vibration measurement, frequency is typically expressed in Hertz (Hz), which represents the number of cycles per second.Â
When measuring vibration, the frequency of the vibration signal can provide important information about the underlying source of the vibration. For example, different components of a machine may vibrate at different frequencies depending on their rotational speed, size, and other characteristics.Â
By analyzing the frequency spectrum of a vibration signal, it is possible to identify the specific frequency components that are associated with different machine components and diagnose potential problems such as imbalances, misalignments, bearing defects, and other faults.Â
Vibration measurement instruments such as accelerometers and vibration meters are typically equipped with frequency analysis capabilities, which enable users to perform spectral analysis of vibration signals and identify the dominant frequencies and amplitudes.Â
In addition, specialized software tools are available that can automatically detect and diagnose specific fault conditions based on the frequency content of vibration signals.
PhaseÂ
Phase is another important parameter in vibration measurement, which describes the relative position of a vibrating object in its oscillatory cycle. In the context of vibration measurement, phase is typically measured in degrees and represents the angular position of a vibration signal relative to a reference signal.
When measuring vibration, phase can provide important information about the relationship between different vibration signals and the underlying sources of the vibration. For example, phase measurements can be used to identify the presence of resonances, determine the alignment of rotating machinery components, and detect imbalances and other faults.
In vibration measurement, phase is often measured using a reference signal, such as a tachometer signal or a signal from a known vibration source. The phase of the vibration signal is then compared to the phase of the reference signal to determine the phase difference, which is typically expressed in degrees or radians.
One common technique for measuring phase in vibration analysis is the use of phase analysis software, which can calculate the phase difference between two vibration signals and display the results graphically. This can help identify patterns and trends in the vibration signal that may be indicative of specific fault conditions or other issues.
VelocityÂ
Velocity is another important parameter in vibration measurement, which describes the speed at which a vibrating object is moving at a specific point in time. In the context of vibration measurement, velocity is typically expressed in units of meters per second (m/s) or inches per second (in/s).
When measuring vibration, velocity is a useful parameter because it is directly related to the amplitude of the vibration signal. Specifically, velocity is proportional to the rate of change of displacement, which is the distance that the vibrating object moves from its equilibrium position. This means that a higher velocity reading indicates a greater displacement of the vibrating object, and therefore a larger vibration amplitude.
Velocity measurements are often used in vibration analysis to assess the severity of vibration and to compare the vibration levels of different machinery or components. In addition, velocity measurements can be used to identify the frequency of the vibration signal, which is important for diagnosing specific fault conditions.
Vibration measurement instruments such as accelerometers and vibration meters are typically equipped with velocity measurement capabilities, which enable users to measure the velocity of a vibration signal in real time. In addition, specialized software tools are available that can perform spectral analysis of vibration signals and automatically calculate velocity values at different frequencies.
Acceleration
Acceleration is a key parameter in vibration measurement as it provides information about the rate at which the velocity of the vibrating object is changing. Acceleration is measured in units of meters per second squared (m/s²) or in terms of gravity (g).
In vibration measurement, acceleration is often used to characterize the severity of vibration. The higher the acceleration, the more severe the vibration.
Accelerometers are commonly used to measure acceleration in vibration measurement. These devices can be mounted directly on the vibrating object or on a fixed structure near the object. The accelerometer converts the mechanical vibration into an electrical signal, which is then analyzed by a vibration analyzer.
Accelerometers are sensitive to both high and low frequencies, which makes them useful for measuring a wide range of vibrations. They are also able to measure transient events, such as shocks and impacts.
In summary, acceleration is an important parameter in vibration measurement, and accelerometers are commonly used to measure acceleration in a variety of applications.Â
DisplacementÂ
Displacement in vibration measurement refers to the distance that an object moves from its equilibrium position during a vibration cycle. It is one of the primary parameters used to describe vibration, along with velocity and acceleration.
Displacement can be measured in various units, including meters, millimeters, or micrometers, depending on the sensitivity and accuracy of the measurement equipment. The displacement measurement is usually taken with respect to a reference point or position, which is often the equilibrium position of the vibrating object.
In general, displacement is a useful parameter for describing the behavior of structures and machines subjected to vibration. It can help in identifying potential problems, such as excessive wear and tear, misalignment, or unbalanced parts, which can cause further damage or failure. Additionally, displacement measurement can also be used to evaluate the effectiveness of vibration mitigation strategies, such as the use of vibration isolators or dampers.
ShockÂ
Shock in vibration measurement refers to a sudden and short-duration acceleration event that can cause damage to a structure or component. It is a type of transient vibration that can occur due to various sources such as impacts, explosions, or sudden changes in velocity.
Shock can be measured using an accelerometer, which is a device that detects acceleration and converts it into an electrical signal. The measurement of shock is typically expressed in terms of the peak acceleration value, the duration of the shock event, and the frequency content of the shock waveform.
Shock can cause significant damage to structures and components, especially those that are not designed to withstand high levels of acceleration. For example, electronic devices, fragile equipment, and mechanical components can be damaged or even destroyed by a shock event. Therefore, it is essential to measure and analyze shock vibrations to ensure the safety and reliability of the equipment and the surrounding environment.
In general, shock measurement is important in various applications, including aerospace, automotive, and defense industries, where high levels of shock can be expected. The measurement and analysis of shock vibrations can help in identifying potential problems, optimizing design, and developing effective mitigation strategies.
These parameters can be measured using various types of sensors, such as accelerometers, velocity transducers, and displacement transducers. Vibration analysis software can be used to analyze the data and provide insight into the behavior of the object or system being measured.
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