Chemical Engineering December 2022 - 33

forces within the system, like that
achieved in an Operating Deflection
Shape, there is another critical diagnostic
piece of information when
dealing with pumping systems: At
what frequency is the vibration occurring,
and what are the natural
frequencies? Every system has several
inherent natural frequencies.
When these natural frequencies are
matched (or " excited " ) by a forcing
frequency in the system, such as
1x operating speed, they resonate.
This resonance automatically amplifies
the vibration level, and generally
makes for a very bad day. When
your pumping system " sings " in this
manner, it is not music to the ear,
but rather a headache.
These natural frequencies can be
detected by intentionally impacting
the object and then measuring the
frequencies at which it naturally vibrates.
While often done with an accelerometer,
or several if the shape
of the motion is being characterized,
this can now be achieved quickly
and comprehensively using video.
Since the vibration after impact is
generally very short in duration, several
impacts can be " averaged " together,
which reduces the noise floor,
thus lowering the detection threshold.
This lower detection threshold
makes natural-frequency characterization
using video possible, even
while equipment is operating.
In addition to natural frequency
characterization, is it useful to analyze
trends
in low-level vibration
over time to understand how the
condition is changing. If the detection
threshold is too high, then the
user must wait until the vibration
levels are problematic to the point
of requiring action before employing
the technology. But the aforementioned
averaging capability can also
be applied using a keyphasor or
similar signal to trigger multiple videos
for averaging. This reduces the
noise floor, and lowers the detection
threshold, so that vibration issues
can be monitored and understood
well before they require intervention.
This can be useful for early-stage
diagnosis of impending problems
that have a certain characteristic
frequency, since the video pixel intensity
variation detected in this
manner can be analyzed by fastFourier
transform (FFT), and then
the vibration-versus-frequency
spectrum at each pixel can be determined
by the motion magnification
system. Various vibration levels,
or changes in those levels, at key
frequencies, can be excellent telltales
for machinery diagnosis and
prognosis, as discussed in the ISO
13373 series of standards.
Video testing simplifies the measurement
and visualization of vibration
on pump systems, enabling
rapid diagnosis of vibration issues. n
Edited by Scott Jenkins
Author
Chad Pasho is the director of business
development for Mechanical
Solutions, Inc. (MSI; 11 Apollo Drive,
Whippany, NJ 07981; Email: chad.
pasho@mechsol.com). Since joining
MSI in 2014, Pasho has focused
on rotating machinery diagnostics
and development,
and
several high-speed video characterization
products, including VibVue
for characterizing vibration and motion magnification.
Pasho's previous experience includes technical and management
roles at Schlumberger, Octave Communications
(now Polycom), and NextEra Energy. He has an MBA from
the Olin Graduate School of Business at Babson College,
and a B.S.Ch.E. from Worcester Polytechnic Institute.
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