VIBRATION MEASUREMENT In some practical situations, it might be difficult to develop a mathematical model of the system and predict its vibration characteristics through an analytical study. In such cases, we can use experimental methods to measure the vibration response of the system to a known input. This helps in identifying the system in terms of its mass, stiffness, and damping. In practice the measurement of vibration becomes necessary for the following reasons: 1.
The increasing demands of higher productivity lead to higher operating speeds of machinery and efficient use of materials through lightweight structures. These trends make the occurrence of resonant conditions more frequent during the operation of machinery and reduce the reliability of the system. Hence the periodic measurement of vibration of machinery and structures becomes essential to ensure adequate safety margins. Any observed shift in the natural frequencies or other vibration characteristics will indicate either a failure or a need for maintenance of the machine. 2.
The measurement of the natural frequencies of a structure or machine is useful in selecting the operational speeds of nearby machinery to avoid resonant conditions. 3. The theoretically vibration characteristics of a machine or structure may be different from the actual values due to the assumptions made in the analysis. 4. The measurement of frequencies of vibration and the forces developed is necessary in the design and operation of active vibration-isolation systems. 5. In many applications, the survivability of a structure or machine in a specified vibration environment is to be determined.
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If the structure or machine can perform the expected task even after completion of testing under the specified vibration environment, it is expected to survive the specified conditions. 6. Continuous systems are often approximated as multi-degree-of-freedom systems for simplicity. If the measured natural frequencies and mode shapes of a continuous system are comparable to the computed natural frequencies and mode shapes of the multi-degree of- freedom model, then the approximation will be proved to be a valid one. . The measurement of input and the resulting output vibration of a system help in identifying the system in terms of its mass, stiffness, and damping. 8. The information about ground vibrations due to earthquakes, fluctuating wind velocities on structures, random variation of ocean waves, and road surface roughness are important in the design of structures, machines, oil platforms, and vehicle suspension systems.
In general, a transducer is a device that transforms changes in mechanical quantities (such as displacement, velocity, acceleration, or force) into changes in electrical quantities (such as voltage or current). Since the output signal (voltage or current) of a transducer is too small to be recorded directly, a signal conversion instrument is used to amplify the signal to the required value.
The output from the signal conversion instrument can be presented on a display unit for visual inspection, or recorded by a recording unit, or stored in a computer for later use. The data can then be analyzed to determine the desired vibration characteristics of the machine or structure. Depending on the quantity measured, a vibration measuring instrument is called a vibrometer, a velocity meter, an accelerometer, a phase meter, or a frequency meter. Reference link: http://classof1. com/homework-help/engineering-homework-help
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