Vibration - Greenheck MOA Installation, Operation And Maintenance Manual

Vibration

In Situ Vibration/Resonance Analysis
Resonance characteristics of the fan array must be checked in operation once field installed to determine interaction
with the environment, and if necessary modified.
The vibration level of the fan array must be determined and regions above the limit value avoided. Resonance also
must be identified and avoided during normal operation.
Regular observation of resonance points is necessary, at the very least at the intervals demanded in the operating
instructions.
The vibration characteristics must be determined at least in the axial direction and transversely throughout.
Measurement of the vibration in all three axes is recommended and should be performed over the entire speed range
to obtain a complete picture of the vibrations occurring in the application.
• Repetition of measurements: Every 6 months.
• Increase the speed gradually, by 5 Hz for example, and note down the readings in a table.
Speed in
Speed in Hz
rpm
20 Hz
35 Hz
... .
... .
60 Hz
Proposal for measurement protocol
• For rigidly mounted fans, recommended in-situ vibration velocities of less than .250 in./sec in accordance with
AMCA 204 and BV-3 grades.
Vibration Measurement on MOA Fan Array
An appropriate method is measurement at the motor fastening diameter on the motor support plate in the direction
of the motor axis of rotation and perpendicular to this.
Action to be Taken in the Event of Excessive Vibration Loading
• Pass through point of resonance quickly on start-up.
• Always avoid resonant operation.
• Modify the design of the device/installation, e.g., using reinforcement braces.
22 Modular Open Array
Vibration velocity in axis
direction in in./sec (rms value)
Vibration velocity
perpendicular to axis direction
in in./sec (rms value)
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