Vibration Analysis

(a) Briefly describe the use of vibration measurement as a tool in condition monitoring of rotating machinery. Your answer should include:

• definitions of the quantities which can be usefully measured.
• the application to fault identification in rotating machinery.
• the typical transducer used for the task.

(b) A machine runs on rolling element bearings at a shaft speed of 3200 rpm. The bearings have the following characteristics: roller/race diameter ratio = 0.23, number of rolling elements 11, contact angle 0°. The machine is classified as Class II for the purpose of assessment under ISO 2372.

• Assuming that the vibration can be described by a dominant frequency component of the form x(t) = A sin(2Πft) calculate the vibration frequencies which would correspond to shaft and bearing faults occurring in this machine.

• Using the ISO 2372 table, estimate the range of acceleration amplitudes which should be measureable in order to record the bearing's performance up to the ‘unacceptable' threshold.

• If an accelerometer of sensitivity 100 mV/g is used to detect the vibrationestimate the maximum voltage amplitude which should be measureable.

(c) It is necessary to select an A/D converter to capture the vibration signals from the accelerometer. Using the results from part (b) above to estimate the required frequency range and frequency resolution of the measurement as well as the dynamic range of the data: specify

• A suitable resolution for the A/D converter,
• A suitable sampling frequency for the measurement,
• The number of samples that should be recorded for each spectrum
• Any other signal conditioning elements that may be necessary.