Vibration testing
failures. All test shutdowns result in the
drive signal smoothly ramping down to
zero. External shutdowns are monitored
using a digital input in the signal
processing hardware that instantaneously
ramps down the shaker drive signal.
TABLE HEALTH CONTROL SYSTEM
This is a computer and sensor system that
protects a high-value test article from
potential damage due to unexpected
vibrations, should failure of the vibration
test system occur during testing. The Table
Health Control System monitors various
subsystems including overall hydraulic
supply pressure, hydrostatic supply
pressure locally at each bearing, and
pneumatic pressure and position of the air
isolation system. It also provides
communication between the interlocks
and the vibration controller. It must
provide a ‘permissive’ signal, indicating
that all systems and the table are working
and in the proper state, for the vibration
controller to start a test.
Upon detection of a fault condition, the
Table Health Control System will stop the
vibration test at a user-definable rampdown
rate. It also controls the startup
90 SHOWCASE \\ AEROSPACETESTINGINTERNATIONAL.COM
operations for the shaker systems, bringing
the vibration test system from park to the
operative state in a controlled manner. At
the end of testing, the Table Health Control
System turns off the hydrostatic bearing
and air isolator.
A PROPRIETARY VIBRATION
CONTROL SYSTEM
The vibration controller has modifications
to the sine signal generation code to ensure
that all shutdowns from the controller
include a 400ms ramp-down. The sine
signal generation code runs in the digital
signal processor hardware on the
controller front-end and receives
instructions from the control loop
processing code. A watchdog feature looks
for instructions from the control loop. If
the control loop does not issue a command
to the drive generation within the
expected time, a soft shutdown is initiated.
This mitigates risk of over-test due to
controller malfunction.
All interlocks are connected to a trigger
input in the controller hardware front-end.
The trigger input is continuously
monitored to detect a trip of one of the
interlocks. Trip of an interlock will initiate
a soft shutdown within a few milliseconds.
An uninterruptible power supply (UPS)
provides the ability to continue operation
of the vibration controller instrumentation
after loss of power. Should power loss
occur, the UPS signals the controller to
initiate a soft shutdown.
MODIFIED AMPLIFIERS
The amplifiers that deliver power to the
electrodynamic shakers are designed to
support a soft shutdown after complete loss
of power. Modifications to the amplifier
include larger capacitors and a UPS that
supplies power to IO modulators. Given a
power loss event, these features enable
continued operation so the controller can
smoothly shut down the test.
With the experience gained from the
significant projects at NASA’s Plum Brook
and Goddard facilities, Data Physics
and Team will endeavor to advance the
satellite testing capabilities at the UK’s new
NSTF facility. \\
Kevin W. McIntosh is general manager of
Vibration Test Systems at Data Physics and Team
Corporation and Thomas Reilly is general manager
of Instruments at Data Physics
4 & 5 // Model showing
Data Physics’ and Team
Corporation’s horizontal
and vertical vibration
systems at the National
Satellite Test Facility RAL
Space, UK
6 // Artists impression
of the National Satellite
Test Facility
/AEROSPACETESTINGINTERNATIONAL.COM