TAILIEUCHUNG - Vibration Fundamentals Episode 3

Tham khảo tài liệu 'vibration fundamentals episode 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 54 Vibration Fundamentals In applications where the coiled cable distorts or interferes with the accuracy of acquired data a shielded coaxial cable should be used. Although these noncoiled cables can be more difficult to use in conjunction with a portable analyzer they are absolutely essential for low-speed and electromagnetic field applications. Data Measurements Most vibration monitoring programs rely on data acquired from the machine housing or bearing caps. The only exceptions are applications that require direct measurement of actual shaft displacement to obtain an accurate picture of the machine s dynamics. This section discusses the number and orientation of measurement points required to profile a machine s vibration characteristics. The fact that both normal and abnormal machine dynamics tend to generate unbalanced forces in one or more directions increases the analyst s ability to determine the root-cause of deviations in the machine s operating condition. Because of this measurements should be taken in both radial and axial orientations. Radial Orientation Radially oriented measurements permit the analyst to understand the relationship of vibration levels generated by machine components where the forces are perpendicular to the shaft s centerline. For example mechanical imbalance generates radial forces in all directions but misalignment generally results in a radial force in a single direction that corresponds with the misaligned direction. The ability to determine the actual displacement direction of the machine s shaft and other components greatly improves diagnostic accuracy. Two radial measurement points located 90 degrees apart are required at each bearing cap. The two points permit the analyst to calculate the actual direction and relative amplitude of any displacement that is present within the machine. Figure illustrates a simple vector analysis where the vertical and horizontal radial readings acquired from the outboard bearing cap indicate

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