To approach the problem of vibration analysis theoretically can be cumbersome and inaccurate and to rely on manual methods such as felling by hand, listening for noise changes or placing a coin on the machine housing is inadequate for today’s quality standards. Using modern instrumentation and transducers it is a simple procedure to reduce machine unbalance to acceptable levels and ensures natural frequencies occur safely outside operational speed ranges. BSI, ISO, DIN, and VDI specifications have been established to define evaluation limits for vibrational behavior of different machine types.
Frequency and modal or structural analysis tests on components or fully assembled equipment characterize vibrational behavior and provide information for any corrective measures. One of a range of portable instruments to perform these tests is the multifunction vibroport.
In most instances the instrument is used in conjunction with an electro-dynamic transducer which is held against the measuring position attached by metallic clamp or secure by studs. Recommended measuring locations in most instances are the bearing and the machine mounting points.
A frequecy analysis test resolves the vibration signature picked up by the transducer into individual excitation components and their corresponding amplitudes. The information is displayed digitally or, if required, the complete frequency spectrum can be output by using an X-Y recorder. From knowledge of fundamental rotating or reciprocating frequencies, it is possible to identify the source of undesirable vibration.
When examining the dynamic properties of machines, individual components of foundations, a full structural analysis is required. This determines the relationship between an applied excitation force and the resulting output vibration characteristics – the transfer function. An instrument such as vibroport induces an input reference frequency through an electro-dynamic exciter. From a pick up transducer, output amplitude, phase-angle and frequency information is generated. These parameters can be represented in the form of a polar plot called a Nyquist diagram, from which it is possible to determine the natural frequency and modes, dynamic stiffness and damping factors of the machine. Based on these results, the engineer can asses whether simple design changes are required for reliable operation and performance.