data acquisition
VIBRATION CONTROL SYSTEM
Early closed-loop vibration control
systems, though an improvement
over the first generation signal
generators, could only afford the
end-user a handful of channels and
test modes. Modern ones, like
m+p VibControl, offer over one
hundred channels in the active
control loop and almost unlimited
testing capability.
Due to the increasing complexity
of spacecraft and the shakers that
test them, it is sometimes necessary
to have many accelerometers in the
primary control loop average, which
produces single or multiple drive signals. A
secondary control loop can also be used for
‘watchdog’ channels that can notch or limit
the drive signal within specific frequencies
in order to protect sensitive optics,
instruments, or even the spacecraft’s
composite structure itself.
The m+p VibControl system can have up
to 128 channels in both the primary and
secondary control loops all while
performing calculations on pseudochannels
(which can also be limited) to
monitor overturning moment, force and
even geometric vector-RSS calculations for
off-axis accelerometers. While controlling
the vibration test, this system can also
66 SHOWCASE 2020 \\ AEROSPACETESTINGINTERNATIONAL.COM
store high-frequency time domain data for
advanced post-test analysis for a subset or
for all the channels, including notch or
limit channels. Built-in bridge modules can
now provide dynamic notching for stress/
strain gauges and pressure sensors for an
added layer of control.
DATA ACQUISITION SYSTEM
Most large structures require frequency
and time domain recorded data in addition
to the channels acquired by the control
system. These additional channels can be
useful for many things from determining
the quality of workmanship of a
component to characterizing the operating
deflection shapes or even validating a
systems Finite Element Model. A modern
systems can provide a nearly unlimited
number of channels for which to acquire
this data. And more.
For example, the James Webb Space
Telescope (JWST) recently utilized a
256-channel system from m+p
international to not only record
acceleration in sinusoidal sweep harmonic
plots and time domain data during
vibration testing but also as a ‘watchdog’
system to abort a vibration test should any
of the aforementioned channels reach their
limits. In this case, a test was aborted
during a sine sweep when one of the
spacecraft’s critical components saw
acceleration levels above the prescribed
limit by opening an enable-loop that
signaled a safe shutdown of the control
system. The analysis team responsible for
the JWST was able to use the recorded data
to determine a safe path forward and
ultimately completed the test successfully.
POST-TEST ANALYSIS SYSTEM
Just as critical as acquiring the data from a
dynamic test, is analyzing the data to
determine the test’s efficacy and
comprehensiveness. While every major
spacecraft manufacturer and agency has a
viable way to process their data, some are
more efficient than others and have been
able to bypass the typical report-thenanalyze
system of the past in favor of a
more synergistic system.
One manufacturer, in particular,
has employed the use of an offline
version of m+p international’s
control software on several
workstations networked to both the
vibration control system and data
acquisition systems. This
configuration makes it possible
to instantaneously deliver all
data acquired during testing
directly to the analysis group for
post-processing.
Whenever time domain
processing or more advanced
calculations are needed, the group employs
the use of m+p Analyzer software to
complete the task. This configuration saves
hours of single-line-flow in between the
graduated testing levels and axes and frees
the test engineers to perform concurrent
tasks like making test preparations,
repairing instrumentation and checking
the health of their shaker system.
THE COMPLETE SYSTEM
At its worst, technology can be used to
react to the errors of the past. At its best, it
can predict and prevent future failures,
working together elegantly to assist our
most advanced endeavors. The spacecraft
that are sent to the cosmos can do
everything from providing information to
remote parts of the world to hopefully
providing answers to the myriad questions
about the origins of our universe.
Whatever the mission, the spacecraft
manufacturers are primarily concerned
with efficiency and risk. Increasing
efficiency. Reducing risk.
With respect to just one small part of
the monumental task that is testing a
spacecraft, m+p international has made
enormous strides to increase the efficiency
and reduce the risk of vibration testing.
This has been done by combining a
revolutionary, standalone Monitor System
with both a reliable Vibration Controller
and extensive Data Acquisition System and
finally networking all three to an
extremely capable Post-Processing and
Analysis system.
Though some of the aforementioned
features are forward-looking, most are
aerospace community requests, special
developments, or ideas incorporated from
the end-users of the systems. m+p
international as one of the premier
providers of these types of systems
remains so precisely because they continue
to listen to their customers. This
community-driven spirit produces systems
that are robust but easy to use. Powerful
yet personal. \\
Dale A. Schick is area sales manager with m+p
international
4 // Online data reduction
during closed-loop sine
vibration test
5 // Rack mounted highchannel
count hardware
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