tailieunhanh - Rotating Machinery Vibration 2011 Part 11

Tham khảo tài liệu 'rotating machinery vibration 2011 part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 232 Chapter 7 With the magnet essentially stationary in the transducer s frequency range of use typically 10 to 1 500 Hz vibration of the electrical coil rigidly attached to the housing causes the magnetic flux lines to induce a voltage in the coil proportional to velocity of housing vibration. Thus a velocity transducer produces a selfgenerated low-impedance velocity-proportional electrical signal which can be fed to monitoring and data acquisition systems without additional signal conditioning. Velocity transducers are therefore popular in many rotating machinery applications. However because a velocity transducer has internal moving parts its use is less popular in hostile environments where relatively higher ruggedness is demanded as more inherent with an accelerometer. . Displacement Transducers . Background The internals of many types of rotating machinery especially turbomachinery have a number of quite small annular radial clearance gaps between the rotor and the stator . journal bearings annular seals balance drums and blade-tip clearances. Therefore one obvious potential consequence of excessive rotor vibration is rotor-stator rubbing contact or worse impacting. Both accelerometers and velocity transducers measure vibration of nonrotating parts of a machine and thus cannot provide any direct information on rotor motion relative to the stator. The importance of rotor motion relative to stator motion led to the development of transducers to provide continuous instantaneous rotor-to-stator position measurements typically at each journal bearing. The earliest rotor-stator position measurement device widely applied is commonly referred to as a shaft rider and it is kinematically similar to a typical spring-loaded IC engine valve tracking its cam profile. That is a shaft rider is essentially a radial stick that is spring loaded against the journal to track the journal radial motion relative to a fixed point on the nonrotating part of the machine .