Efficient Plant November 2017 - 32

feature | pdm solutions

Fig 2. The Yokogawa wireless vibration-monitoring system consists of a piezo-electric vibration sensor connected to a host system by way of a wireless mesh network. The sensor can be mounted using
a pedestal screwed to the equipment, i.e., target device, housing (in this case, a motor's housing),
usually near the bearings.

While vibration
can't be
eliminated
entirely, it can
be measured
and analyzed
to guide
corrective
actions.

| EFFICIENTPLANTMAG.COM

which has a variety of causes, is one of the
greatest enemies of rotating equipment.
"Consider," he said, "a typical ANSI
pump driven by a motor with a flexible
coupling. If the two shafts aren't truly on a
common centerline, the coupling will compensate for the misalignment, but it will
likely introduce vibration into the installation. Vibration creates detrimental forces
within the ball bearings, causing premature
wear, which further increases the overall
vibration. Over a long-enough period of
time, the problem will compound until one
or more of the bearings fail. The pump's
mechanical seals may also suffer damage
and begin to leak. Before long, the installation must be shut down and overhauled."

In addition to the vibration inherent
with any rotating equipment, at least at
some level, potentially harmful vibration
can also be transmitted by way of piping
and support structures from other machinery within the process unit. The good news
is that, while vibration can't be eliminated
entirely, it can be measured and analyzed to
guide corrective action.
Sensors are available to characterize
and quantify the amount of vibration, and
to capture characteristic patterns, often
referred to as signatures. These monitoring
systems typically use a piezo-electric sensor
to create and transmit a signal proportional
to measured vibration.
Vibration sensors have been available for
many years, but older systems were costly
to install, limiting their deployment to the
most expensive and critical rotating equipment. For other installations, technicians
have carried portable units on routine plant
inspections and manually checked bearings, seals, and other critical points.
According to Yamamoto, sophisticated
portable systems can capture historical
information and compare specific installations over time, but such rounds also can
be time-consuming and, ultimately, costly.
"Furthermore," he noted, "in plants with
minimal head counts, they can be delayed
or skipped when more pressing tasks
emerge."

ADVANTAGES OF
CONTINUOUS MONITORING
Short of a catastrophic failure of some
component, vibration problems don't
usually advance drastically in a brief period
of time. This fact is usually cited to support
the idea of periodic inspections. "Unfortunately," Yamamoto explained, "vibration
problems may increase slowly until they
reach a critical point, and then the climb
becomes much steeper toward failure, all
of which can easily occur before the next

NOVEMBER 2017

http://www.EFFICIENTPLANTMAG.COM

Table of Contents for the Digital Edition of Efficient Plant November 2017