Vibration analysis

Press the down arrow to display the readings of vibration velocity (mm/s or inch/s), or displacement (µm or mils) if selected, broken down into each of 3 bands.

 

The display shows the vibration level in frequency ranges that are all based on multiples (1X, 2X and 3X) of the specified Run Speed of the machine as displayed beneath the 3 bar graphs.

In order to perform a vibration analysis it is important that the running speed of the machine is entered correctly. This can be done with the Setup Wizard. Go to Configuration.

The frequency ranges of the VA bands are based on the following multiples of running speed:

1X = Unbalance

The level of vibration in the frequency band based on the running speed is usually indicative of how well balanced the machine is. A large vibration at the running speed usually indicates that the machine is out of balance. However even a very well balanced machine will typically show some vibration at the running speed but this figure should ideally be quite low (e.g. typically less than about 2 mm/sec for a medium sized machine).

2X = Misalignment

A high level of vibration in the frequency band centerd at twice the running speed is a possible indication of misalignment. This is based on the fact that shaft misalignment can result in a double peak in the waveform due to there being two different centers of gravity (one from each shaft). In other words the accelerometer picks up a peak as each center of gravity passes by and hence there will be two positive and two negative peaks each revolution of the shaft. This will typically give rise to a vibration signal at double the running speed of the machine.

3X = Looseness:

High vibration in the frequency band centerd at 3 times running speed is a possible indication that something may be loose (e.g. loose mounting bolts, weak foundations etc.) as it is not usual to see third order vibration in a machine unless there is some structural looseness that is being “excited” by the vibration of the machine.

Frequency spectrum

Press the down arrow button once more to display vibration levels shown as a frequency spectrum in the range from 0 to 1kHz. The heights of the peaks indicate the RMS vibration level (in mm/s or inch/s) at each frequency point in the spectrum. The readings to the right of the screen show the frequency (in Hz or CPM) and the RMS vibration level (in mm/s or inch/s) at the position of the cursor (red dotted line). The cursor position can be moved by use of the left (<) and right (>) arrow buttons.

Pressing the down arrow button increases the resolution of the frequency axis from 100 Lines (i.e. 10Hz or 600 RPM resolution) to 800 Lines (i.e. 1.25Hz or 75 RPM resolution). Increasing the resolution effectively zooms into the frequency spectrum. In order to display the full spectrum at the higher resolution the display must be scrolled using the left and right arrow buttons.