Page 83 - Intro Predictive Maintenance

5

MACHINE-TRAIN MONITORING

PARAMETERS

This chapter discusses normal failure modes, monitoring techniques that can prevent
premature failures, and the measurement points required for monitoring common
machine-train components. Understanding the specific location and orientation of each
measurement point is critical to diagnosing incipient problems.

The frequency-domain, or FFT, signature acquired at each measurement point is an
actual representation of the individual machine-train component’s motion at that point
on the machine. Without knowing the specific location and orientation, it is difficult—
if not impossible—to correctly identify incipient problems. In simple terms, the FFT
signature is a photograph of the mechanical motion of a machine-train in a specific
direction and at a specific point and time.

The vibration-monitoring process requires a large quantity of data to be collected, tem-
porarily stored, and downloaded to a more powerful computer for permanent storage
and analysis. In addition, there are many aspects to collecting meaningful data. Data
collection generally is accomplished using microprocessor-based data collection
equipment referred to as vibration analyzers; however, before analyzers can be used,
it is necessary to set up a database with the data collection and analysis parameters.
The term narrowband refers to a specific frequency window that is monitored because
of the knowledge that potential problems may occur as a result of known machine
components or characteristics in this frequency range.

The orientation of each measurement point is an important consideration during the
database setup and analysis. Each measurement point on every machine-train in a pre-
dictive maintenance program has an optimum orientation. For example, a helical gear
set creates specific force vectors during normal operation. As the gear set degrades,
these force vectors transmit the maximum vibration components. If only one radial

74