High-speed imaging
fast-acting adhesives. The leads of the
strain gauge ran to the signal conditioning
circuit, which consisted of a wheatstone
bridge with a resistance value roughly
equivalent to that of the strain gauge. By
monitoring the digital signal coming from
the strain gauge, users can immediately
see the strain gauge resonating at its
natural frequency. They can also use the
strain gauge to visualize any impact to the
tuning fork system—including deflection
and vibration.
Interestingly, aerospace researchers can
use the high-speed camera to validate the
strain gauge measurements. Images can be
post-processed to plot a position versus
time graph, which coincides directly with
the data collected by the DAQ. By taking
FFTs from both the strain gauge and image
data, users can determine the vibrational
modes present during the event.
CAMERA SIGNALS
Most high-speed camera systems include a
BNC-port interface to carry available I/O
signals, including the f-sync, strobe, ready,
recording and image-based auto trigger
signal. To see one or more of these signals
relative to the captured video, users can
simply connect the signals in the back of
the camera to the DAQ unit.
This third example visualizes the strobe
signal—a square wave that determines
both the frequency and degree of exposure
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134 SHOWCASE 2020 \\ AEROSPACETESTINGINTERNATIONAL.COM
time—with respect to the light source. This
method is quite useful for aerospace
testing, as it is traditionally difficult to
synchronize strobe lights with high-speed
video. By seeing the strobe signal relative
to the light signal, users can easily shift—
i.e., delay—the strobe signal or light pulse
in a way that optimizes the amount of
light. Visualizing the strobe in the
software also lets users see where it exists
relative to other trigger signals present in
the system. Collecting such data also
allows users to compute the standard
deviation—or other statistics—in the
strobe signal pulse.
IMAGE-BASED AUTO TRIGGER
Image-based auto trigger (IBAT)
automatically triggers a Phantom camera
when motion is detected. This feature is
particularly impressive, as its minimum
trigger time is within one frame. At a
frame rate of 1 million frames per second
(fps), for example, IBAT can trigger the
camera within 1 microsecond of detected
motion. This feat would be otherwise
impossible to achieve without the use of a
field programmable gate array, or FPGA—a
massive parallel logic gate that can process
images in near real-time.
IBAT automatically triggers the camera
as soon as an object passes through the
camera’s field of view (FOV) and is a useful
tool for characterizing inconsistent
processes—including observing foreign
object damage. This fourth example shows
the IBAT signal falling when an object
moves through the FOV.
EXAMPLE 5: THERMOCOUPLE
Flames and explosions are another area of
interest for many aerospace engineers. In
addition to visualizing the flame profile,
researchers may want to know the
temperature of the flame with respect to
space and time. An excellent way to obtain
this information is to synchronize highspeed
video with the analog data coming
from a thermocouple. In this final example,
a household lighter rapidly heats a type K
thermocouple—enabling users to easily
correlate the image’s visual
thermodynamics with the measured
temperature profile. Analyzing the data
reveals a rapid rise in temperature,
followed by a classic cooling curve.
The value proposition of a combined
high-speed imaging and DAQ system may
seem obvious to any researcher studying
fast moving objects or events—from rocket
launches to ballistics. In practice, however,
bringing these two systems of
measurement together has not been easy
given the differences between imaging and
DAQ workflows. By creating a link
between high-speed cameras, off-the-shelf
DAQ hardware and PCC software,
aerospace researchers now have a unified
tool to see what they have been measuring
– ultimately providing more insight into
the subject at hand. \\
Kyle Gilroy is a field application expert at Vision
Research
3 // A high-speed camera
can be used to validate
strain gauge
measurements, as in this
example which shows a
tuning fork and the
resulting position versus
time graph
4 // High-speed video can
be synchronized with the
analog data produced by a
thermocouple
“data fusion lets
researchers visualize the
synchronized video and
analog data side by side”
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