TABLE OF CONTENTS The proper gathering of vibration data for machinery health monitoring and diagnosis relies on the proper selection of transducers. This chapter deals with the three most common motion transducers: proximeters, velocity pickups, and accelerometers, as well as piezoelectric force transducers, microphones, and piezioelectric pressure transducers.
Since the velocity pickup was the most common vibration transducer available in the early days of predictive maintenance work, the decision as to what parameter should be measured was unconsciously made in favor of velocity (usually in in/sec 0-peak). Some early investigations, attempting to choose the correct parameter, verified that velocity seemed to be a good choice. Certain assumptions about the vibration characteristics of machinery, which were correct only for some classes of equipment, were made. Further thought on this matter, as detailed below, shows that the decision favoring the reading of displacement, velocity, or acceleration levels should be a function of the amplitude values and relative importance of the various forcing frequencies that a machine is capable of generating.
The choice of whether to measure displacement, velocity, or acceleration is not as obvious as one might hope. That a given facility has been measuring displacement or velocity exclusively for many years is a weak excuse for carrying on a tradition that may be incorrect for a certain percentage of the equipment being used in the plant. This section will give the reasons for measuring a particular parameter on a particular machine.
Explanations of the meanings of the terms displacement, velocity,...
