Question

Select the appropriate sensor(s), measure(s) and frequency range to obtain valid vibration data for a single-reduction gearbox driven by a small turbine with rolling element bearings. The turbine operates at 2846 RPM, the output shaft rotates at 987 RPM, the ball pass frequency of the inner race is 8290 CPM, and the gear mesh frequency is 122,378 CPM. Justify your choices.

Answer 1

The appropriate sensor for the given vibrational system is: Piezoelectric Accelerometer Sensors

These sensors uses a highly sensitive piezoelectric crystal, which gives the voltage output, to each vibrational stress caused upon it.

The measures of the sensor depends on the dimension of the system, as the given system is a geared turbine, which generally includes at 200mm*300mm sensor, mounted studly or by an adhesive for optimum measurement of the vibrations.

For the given ball pass frequency of inner race : 8290CPM i.e. 8290 cycles per minute and turbine rotation 2846 RPM, these two are the main factors of a turbine system in creating external vibrations (gear mesh is only dependent on the ball pass frequency), therefore for such system we need a sensor of minimum sensitivity of 100mV/g (100 millivolts/g), and the frequency range must be in between 9000 Hz - 11000 Hz.

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