A permanent and continuous monitoring system offers several
advantages for monitoring cooling towers. The first advantage is the sensors
can be mounted directly on the bearing support parts on the motor and the
gear so bearing condition, as well as casing vibration can be easily and
accurately measured. The two levels of alarm offered by the
CMCP500 Series Monitors
can be set so operators can be made aware of potential problems at early
stages of development before a condition becomes critical, and the second
level of alarm can be used for shutdown.
Low Cost Solution
A continuous monitoring system, such as the CMCP500 Series,
offers a low cost modular system ideally suited to monitoring cooling
towers. Each 500 series monitor includes vibration detection, alert and
danger set points, and alarms with relays.
A standard system, per cell, consists of two accelerometers,
one on the motor inboard bearing and one on the gear near the input shaft
bearing. Both of the accelerometers are mounted in the horizontal plane. Two
CMCP500 Series Monitors are used , one for each sensor, which convert the
sensor signal to a velocity vibration and provide the alarming features.
This system will provide continuous monitoring and protection
for both the drive motor and gear assembly at a minimum level. Alternate
configurations would include a second accelerometer on the outboard bearing
of the motor and a second, or even a third, accelerometer on the gear box.
The second accelerometer would be mounted on the input shaft bearing in the
vertical direction and the third accelerometer would be mounted on the back
side of the gear housing in the axial direction.
System Expansion
A 4-20 mA output signal is provided on all CMCP500 Series
Transmitters and Monitors. This signal can be used as an input for
indicators, chart recorders, a PLC or a DCS system to log and display
vibration levels as well as for trending.
Alarm Set Points
Cooling towers are different from most of the other machinery
in the plant that has continuous monitoring. The same alert and danger set
points for high speed rotating machinery is not applicable to cooling
towers. All cooling towers vibrate more than standard machinery. If the
alarm levels are not set high enough you will be victim to numerous false
shut downs. Alarms set at 0.5 in/sec for alert and 0.8 in/sec for danger would be
unheard of for high speed machinery, but are common on cooling tower gear
assemblies. Also, a longer alarm delay time will avoid false alarms.
