The type of vibration monitoring system to
install on a machine train will depend upon how the machine train is used in the plant
process. A very important machine train will require more instrumentation to monitor its
health and operation condition, while other machine trains having less important roles in
plant operation will have less monitoring requirements. Using the techniques presented in
this application note the machine trains may be classified as critical, essential, or
general purpose. Topics such as how the machine train relates to plant production, plant
and personnel safety, and whether they are spared are used
as classification criteria.
Additionally, costs, such as lost production, replacement, insurance, and maintenance
expenses are factored into this classification.
Critical machine trains are required to maintain plant production and many times are an
integral part of the plant process. They are high capital cost items and must operate
continuously, may not be spared, or have an installed backup unit, because interruption of
the process to startup the backup machine train would have an undesirable effect on the
plant operation. Other machine trains may be involved in an operation which is important
to plant or personnel safety.
Some plant designs that incorporate several identical units may appear to have
installed spares, but all units will be required for 100% plant output. Other plants will
have certain machine trains which are required to operate continuously during emergency
High horsepower and high speed machines would be classified critical if they are
required to operate continuously for extended periods without interruption of the plant
process. All of these machine trains should be considered critical to continued plant
operation and, therefore, qualify for higher expenditure on monitoring instrumentation.
Vibration monitoring instrumentation should
provide continuous, full time monitoring capabilities. Some systems will display every
channel simultaneously so that rapid assessment of the entire machine train can be made.
See STI Application Note, Monitoring Classification, Classif-1 for addition discussion
about monitoring instrumentation.
Essential machine trains may have the same attributes as critical machine trains, but
their importance to the plant production process will not be as important. They may have
installed spare units which can be started without significant interruption of the plant
process. They may be high horsepower or high speed, but will not have to operate for
extended periods or continuously. Maintenance budgets will not be as costly when the
machine fails, thus classifying these machines as essential and will not have the same
monitoring instrumentation requirements as critical machines.
Vibration monitoring systems installed on essential machines can be of a scanning type,
where the systems switches from one sensor to the next to display the sensor output
levels. Many of these systems are controlled with solid state multiplexers and switch
channels every second or so.
General purpose machine trains are all others which are not
classified as critical or essential. They are usually spared and are not critical to plant
production. They usually have auxiliary roles or support other processes, may only operate
on demand, stocked replacement parts, and maintenance costs are relatively low when
compared to critical or essential machine.
Due the machine classification, these machines do not qualify for permanently installed
instrumentation and a continuous monitoring system. These machines are usually monitored
with a portable instrument.
Machine Classification Checklist
- General Purpose