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source, and that source cannot be isolated or turned off for the duration of the measurements, note the source and
magnitude of the vibration before continuing.
•
After it is confirmed that the drive system is "all clear" and the unit access doors are closed, turn the VFD on, and verify
that the fan is turning in the correct direction.
•
Using the VFD, slowly (about 1 RPM increase every five to ten seconds) adjust the motor speed from the lowest limit to
full speed while monitoring the vibration levels. Record the overall vibration levels at regular intervals if desired.
•
As stated previously, when adjusting the VFD speed, proceed slowly while monitoring the vibration levels. If the vibration
value approaches 0.35 ips (0-peak), slowly "zero in" on the speed where the value equals 0.35 ips, and record the speed
at which this occurs as the lower end of the lockout range. Also record the vibration level at this speed.
•
Continue to slowly increase the speed while monitoring the vibration level. If this is a resonance, then the value should
peak and eventually decrease to a level that is below 0.35 ips as the speed is increased. After the vibration level has
peaked and continues to fall, record the speed where the value equals 0.35 ips as the upper end of the lockout range.
•
Using this data, a baseline for vibration history can be developed. The vibration levels can be monitored yearly and the
trend used to indicate potential wear or the need to replace components in the drive system.
•
After the entire speed range has been checked and any resonances identified, ensure the VFD that controls the fan motor
is then turned off, and the power to the motor circuit is locked out.
•
Enter the unit, and carefully remove the accelerometer, along with any associated wiring from the unit.
•
Work with the VFD contractor to enter the lockout speed ranges, if any have been identified, into the VFD, so the unit will
not operate at a resonant speed.
•
Once it has been verified that the drive system is all clear, return the unit to its normal operating condition.
•
Keep a record of any lockout speed ranges for future ref
Vertex™ Evaporative Condenser Operation & Maintenance Manual – Fan Control
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