28
The sign convention is different for the two indicators. If the values for the pump indicator are
positive, the plot will be above and left of the pump shaft reference line. The plot will be below
and right of the pump shaft reference line for positive motor indicator readings.
positive, the plot will be above and left of the pump shaft reference line. The plot will be below
and right of the pump shaft reference line for positive motor indicator readings.
4. Draw a line from the pump indicator point through the motor indicator pump point extending
to the rear motor feet line. This line represents the position of the motor shaft. The vertical
distances from the motor shaft line to the pump shaft line at the two motor feet lines are the
required movements of the motor feet to align the motor to the pump. On the vertical plane plot,
these distances represent the required amount of shims to be added or removed. On the
horizontal plane, these distances represent the amount of lateral movement required at the motor
feet.
to the rear motor feet line. This line represents the position of the motor shaft. The vertical
distances from the motor shaft line to the pump shaft line at the two motor feet lines are the
required movements of the motor feet to align the motor to the pump. On the vertical plane plot,
these distances represent the required amount of shims to be added or removed. On the
horizontal plane, these distances represent the amount of lateral movement required at the motor
feet.
5. After any shimming or movement of the motor, repeat readings and plot data to verify the
alignment.
alignment.
2.9 Vibration Monitoring and Analysis
Vibration monitoring and analysis can be a useful part of a preventive or predictive maintenance
program. There are a variety of vibration monitoring systems available. Some use permanently
mounted sensors to continually monitor vibration levels, while other systems require readings to
be taken periodically with hand held sensors. The type of system used depends on the equipment
being monitored. The maintenance supervisor should compare the potential benefits of a vibration
monitoring system, such as preventing damage and reducing outages, to the overall cost before
deciding which system to use or whether to use any system at all.
program. There are a variety of vibration monitoring systems available. Some use permanently
mounted sensors to continually monitor vibration levels, while other systems require readings to
be taken periodically with hand held sensors. The type of system used depends on the equipment
being monitored. The maintenance supervisor should compare the potential benefits of a vibration
monitoring system, such as preventing damage and reducing outages, to the overall cost before
deciding which system to use or whether to use any system at all.
Proximity Probe System.
A proximity probe is a noncontacting type sensor which provides a
direct current (DC) voltage directly proportional to shaft position relative to the probe. In a
hydroelectric powerplant or a large pumping plant, proximity probes are used to measure the main
shaft runout on the turbine/generator or pump/motor. A typical proximity probe system utilizes
two probes per guide bearing location, radially mounted and 90 degrees apart. The monitors for
the probes are centrally located and are provided with relays for alarm and shutdown with
continuous indication of shaft runout in mils. The optimum alarm and shutdown points will vary
from unit to unit. The best way to set these points is experimentally. The runout amplitude
should be measured from speed-no-load to full load noting the normal amplitude of runout as well
as the amplitude at any rough zones. If operation in the rough zone is not desirable, the alarm
should be set high enough above normal amplitude to prevent nuisance alarms but low enough to
indicate when the unit is in the rough zone. If the operation in the rough zone is allowed, the
alarm point should be set above the maximum amplitude observed at any load. The shutdown
point, if one is desired, should be set high enough to prevent nuisance tripping but low enough to
prevent damage to the machine.
hydroelectric powerplant or a large pumping plant, proximity probes are used to measure the main
shaft runout on the turbine/generator or pump/motor. A typical proximity probe system utilizes
two probes per guide bearing location, radially mounted and 90 degrees apart. The monitors for
the probes are centrally located and are provided with relays for alarm and shutdown with
continuous indication of shaft runout in mils. The optimum alarm and shutdown points will vary
from unit to unit. The best way to set these points is experimentally. The runout amplitude
should be measured from speed-no-load to full load noting the normal amplitude of runout as well
as the amplitude at any rough zones. If operation in the rough zone is not desirable, the alarm
should be set high enough above normal amplitude to prevent nuisance alarms but low enough to
indicate when the unit is in the rough zone. If the operation in the rough zone is allowed, the
alarm point should be set above the maximum amplitude observed at any load. The shutdown
point, if one is desired, should be set high enough to prevent nuisance tripping but low enough to
prevent damage to the machine.
Accelerometer Systems.
There is a number of accelerometer based vibration monitoring systems
available varying greatly in complexity and capability. Accelerometers are light weight vibration