Tham khảo tài liệu 'intro predictive maintenance 2e episode 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Vibration Monitoring and Analysis 167 Axial Of on around or along an axis straight line about which an object rotates or center of rotation. Bearing cap The protective structure that covers bearings. Boundary condition Mathematically defined as a requirement to be met by a solution to a set of differential equations on a specified set of values of the independent variables. Displacement The change in distance or position of an object relative to a reference point usually measured in mils. Dynamics operating Deals with the motion of a system under the influence of forces especially those that originate outside the system under consideration. Fast Fourier Transform FFT A mathematical technique used to convert a time-domain plot into its unique frequency components. Force That influence on a body that causes it to accelerate. Quantitatively it is a vector equal to the body s time rate of change of momentum. Forcing function The cause of each discrete frequency component in a machine-train s vibration signature. Frequency Frequency f is defined as the number of repetitions of a specific forcing function or vibration component over a specific unit of time. It is the inverse of the period p of the vibration and can be expressed in units of cycles per second cps or Hertz Hz . For rotating machinery the frequency is often expressed in vibrations per minute vpm . Frequency circular Another measure of frequency measured in radians w 2p f . Frequency natural All components have one or more natural frequencies that can be excited by an energy source that coincides with or is in proximity to that frequency. The result is a substantial increase in the amplitude of the natural frequency vibration component which is referred to as resonance. Higher levels of 168 An Introduction to Predictive Maintenance input energy can cause catastrophic near instantaneous failure of the machine or structure. Frequency primary The base frequency referred to in a vibration analysis that includes .
