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Technology: Automated fault identification

The critical part of an Online Condition Monitoring System is automated faults identification. It is essential to reliably separate and trend shaft, bearing, gear and electrical related faults as they all exist in similar frequency ranges, often at greatly differing severity levels.

Tensor Systems uses tachometer probes to very accurately measure one or more shaft speeds through the whole of the measurement period. Given the gear tooth numbers, and fft’s of the tacho waveforms, we can calculate exactly which spectral lines are harmonics of which shafts, with the remainder being non synchronous vibration to all shafts.

Rolling element bearings, with the exception of some pure thrust bearings, produce ball pass frequencies which are non synchronous with the shaft they are on, whereas shafts and gears produce synchronous vibrations with the shaft they are on, and sidebands of the meshing partner shafts.

Electric motors also produce non synchronous vibrations due to electro mechanical forces which generate the torque, and they are at known ratios of shaft speed, or in narrow frequency ranges that are known.

This precision separation of sync and non sync vibration, in each spectral band, allows us to reliably separate and trend shaft related, bearing, gear and electrical faults. Bearing numbers are only needed by the analyst to manually confirm the automated diagnostic.

Analyser - Online Condition Monitoring System

Machines don’t always operate at the same speed, load or rotation direction, and the vibration response may be different for each “exact state” of operation.

We measure these 3 operational parameters with the vibration measurement, and place the data in the appropriate “exact state”, in this case being 1 of 8 possibilities, for smooth trending. Each exact state has it’s own vibration limits for each parameter of each measurement and they are based on a “baseline” ratio compared to what is considered “good condition”.

The ratio-metric nature of vibration changes with wear means that it’s not necessary to start with the machine in good condition, as the alarms are set +4db = 1.6x existing vibration for alarm, and +8dB = 2.5x existing vibration for Shutdown.

When an alarm is raised, the alarm must either be lifted or the machine repaired to prevent the alarm, and in most instances, raising the alarm is chosen. There may be many parameters in alarm, so after analysis of the problem, an automated raise can be activated by the user. After a machine has been repaired the user can activate an automated alarm lower action.

To alert key people to the alarm, emails and SMS messages are sent to those people on the list.