140.925-IOM (APR 2019)
Page 23
XLP3 EVAPORATIVE CONDENSERS
OPERATION
NOTICE
The resonant speed identification procedure must be
performed at start-up for units with VFDs.
DANGER
Rotating equipment will cause severe personal injury
or death to persons who come in contact. Do not perform
any service on or near the fans, motors, and drives, or
inside the unit without first ensuring that the fans
and pump motors are disconnected, locked out, and
tagged out.
Recommended
Accelerometer
Location
Figure 21 — Accelerometer Location - Belt Drive
• Connect the signal wire from the accelerometer (provided
by others) to the vibration analyzer (provided by others). Be
sure to route and fasten the wire so that it will not contact
any rotating parts inside the unit when the drive system is
operational.
• Get out of the unit, and ensure that the drive system is “all
clear”. Remove the lockout from the motor circuit.
• With the VFD off, record the vibration level indicated on
the vibration analyzer, and confirm that it is very low
(only picking up ambient vibration). Record this overall
vibration level (0-peak) in inches per second (ips). If the
ambient vibration level is greater than 0.35 ips, identify
and correct the cause of the vibration. It could be
vibration transmitted from another source, instrumentation
malfunction, radio frequency interference, etc. If the cause
is vibration transmitted from another 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
reference.