Variable Speed Machinery

Draglines, Shovels etc.

A lot of important revenue earning machinery in industry does not operate at a constant speed.   Time based vibration analysis techniques are not particularly useful for these types of machines as the data becomes badly smeared by the speed changes during data acquisition. 

The raw vibration signal from an accelerometer is usually recorded, analysed or viewed as a variation in amplitude with respect to time.  This is generally acceptable for a fixed speed machine.  However, for variable speed machines the amplitude variation must be recorded and processed with respect to machine speed and not time (order normalised).

For variable speed machinery, ISS uses a  mixture of DAT and direct to hard drive, multi channel vibration data recording systems.  By acquiring machine speed data from Laser tachometers in parallel with the vibration signals it is possible to record the machine vibration as a function of machine speed and not time.

While these techniques are primarily used for Draglines and Shovels where the machine speed generally varies rapidly,  they can also be used to enhance the accuracy of vibration analysis for nominally constant speed machines.  This applies especially where time synchronous averaging techniques are being used to define localised gear tooth defects.

Examples of variable speed machinery defect noise.