introduction to vibration

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the best way of learning the part of vibration,try this quick learn presentation,if you are a engineer it must be helpful.

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introduction to vibration

  1. 1. Introduction to Vibration and Position Measurements
  2. 2. Copyright Bently Nevada Corporation All Rights Reserved, 1998 © The following marks are Bently Nevada Corporation’s Registered Trade Names: φ MicroPROX ADRE REBAM Keyphasor Proximitor Seismoprobe Key Velomitor TorXimitor Trendmaster Smart Monitor Data Manager Dynamic Data Manager Transient Data Manager Bently Nevada ® ® ® ® ® ® ® ® ® ® ® ® ® ® ®
  3. 3. What is Vibration? Mechanical vibration is the dynamic motion of machine components. Vibration measurement is the measurement of this mechanical vibration relative to a known reference.
  4. 4. How does Vibration Start? Energy must be put into the system through an applied force, either internal or external. The force may be instantaneous, an impulse, or continuous. In machines this energy is diverted from the process. This reduces the machine’s efficiency and may also result in damage to the machine’s components.
  5. 5. What Characteristics are Measured? Amplitude Frequency Phase Angle  Absolute Phase Angle  Relative Phase Angle
  6. 6. What Affects These Characteristics? Mass Spring Stiffness Damping
  7. 7. AMPLITUDE pk 0 pk pk rms Peak-to-peak refers to the total amount of vibration. Zero-to-peak refers to the total amount of vibration from the maximum height of either the positive or negative peak to the zero voltage axis. Root mean square (RMS) is a function of the signal conditioning performed in the monitor or diagnostic instrument and not the output of the transducer.
  8. 8. Frequency Frequency is defined as the repetition rate of a periodic vibration within a unit of time. The frequency of vibration (cycles per minute) is most often expressed in multiples of rotative speed of the machine. Basic frequency measurements can be performed with an oscilloscope and Keyphasor signal.
  9. 9. FREQUENCY TIME/CYCLE
  10. 10. Phase Phase is defined as the timing relationship, in degrees between two or more signals.
  11. 11. PHASE A B TIME (DEGREES) PHASE TIME (DEGREES) A M P L I T U D E PHASE (BETWEEN VIBRATION SIGNALS)
  12. 12. PHASE ANGLE 0° 360° PHASE LAG VIBRATION SIGNAL KEYPHASOR SIGNAL TIME DEGREES OF ROTATION The phase angle is defined as the number of degrees from the Keyphasor pulse to the first positive peak of vibration.
  13. 13. Form Vibration form is the raw waveform displayed on an oscilloscope and can be separated into two categories:  Timebase presentation  Orbit presentation
  14. 14. VIBRATION FORM TIME TIMEBASE- an oscilloscope displays the vibration in units of the transducer (amplitude) versus time horizontally across the display.AMPLITUDE TIME
  15. 15. VIBRATION FORM ORBIT- is the output of two transducers at 90° angles to one another (XY plane) in the X-Y mode of the oscilloscope. The orbit is the representation of the shaft centerline movement. ORBIT Shape
  16. 16. Measurement References The three basic frames of reference for vibration measurements on rotating machines are:  Rotor motion relative to the bearing (Shaft relative Vibration).
  17. 17. MEASUREMENT REFERENCES Shaft Relative
  18. 18. Measurement References The three basic frames of reference for vibration measurements on rotating machines are:  Rotor motion relative to the bearing (Shaft relative Vibration).  Casing motion relative to a fixed reference (Casing Absolute Vibration).  Rotor motion relative to a fixed reference (Shaft Absolute Vibration).
  19. 19. MEASUREMENT REFERENCES Casing Absolute
  20. 20. MEASUREMENT REFERENCES Shaft Absolute
  21. 21. Position Measurements Axial Position Thrust Position Rotor Position Radial Position Differential Expansion Case Expansion Eccentricity
  22. 22. AXIAL POSITION THRUST BEARING ASSEMBLY THRUST PADS THRUST COLLAR
  23. 23. Measurement of the position of the thrust collar in the thrust bearing assembly and how much bearing material may be used up. The probes are mounted on the thrust bearing observing the movement of the rotor position within the thrust bearing. Thrust Position
  24. 24. THRUST POSITION 20 15 10 5 0 20 40 60 80 100 MILS 0.5 1.0 1.5 2.0 2.5 mm0 HOT FLOAT ZONE COLD FLOAT ZONE COUNTER DIRECTION NORMAL DIRECTION
  25. 25. Thrust Position NORMAL/COUNTER Normal - direction the rotor would normally be forced to move due to the designed operation of the machine.  Steam turbine typically Away from high pressure (HP) inlet towards the LP inlet. Counter - direction of thrust opposite the direction the rotor is normally designed to move.  indicates the machine is experiencing an abnormal operation
  26. 26. THRUST POSITION NORMAL DIRECTION NORMAL DIRECTION HP LP LP HP STEAM TURBINE COMPRESSOR
  27. 27. RADIAL POSITION Proximity Probes are used in the X-Y configuration to measure radial vibration, the dc signal from the transducer can be used to indicate the radial position of the rotor within the bearing
  28. 28. DIFFERENTIAL EXPANSION CLEARANCES THRUST BEARING EXPANSION
  29. 29. CASE EXPANSION FIXED FOOT SLIDING FOOT FIXED FOOT FIXED REFERENCE FOUNDATION EXPANSION FRONT STANDARD LVDTs EXPANSION LVDT CASING EXPANSION DUAL CASE EXPANSION SINGLE CASE EXPANSION
  30. 30. ECCENTRICITY SHAFT BOW ECCENTRICITY

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