Existing ultrasonic bolt gages are limited in reliability and resolution
because they only use one point (one zero crossing) in the whole reflected
waveform. Distortions in the echo can cause "peak-jumping" without your
Ultrasonic bolt gages transmit a sound pulse (ultrasonic) into one end of a bolt
and listen for the echo (like sonar).
you tension the bolt it takes a longer time for the echo to return (the bolt
stretches and the speed of sound slows down).
For over 30 years, bolt gages have measured this “echo time” by starting and
stopping a counter (clock). The counter is started when the ultrasonic pulse is
sent out, and the counter is stopped using a single zero-crossing event, in the return echo,
as shown in the Figures below. Tension often induces distortion of the echo which
can cause the
clock to miss a peak with NO display indicating that this peak jumping has
SureBolt outperforms all
other bolt gages by using all of the return echo’s
data. This increases the reliability and accuracy dramatically. The entire
is recorded and compared to the entire new echo when you tension the bolt.
screen graphically overlays and displays the two echoes and lets you see any distortions that
tensioning might cause. Some distortions are caused by moving the ultrasonic
transducer (slipping, off center, loss of coupling, ...), and other distortions are
due to the actual tension in the bolt that deforms the surface of the bolt.
, if there are distortions, you will know this
Because of the distortion factor, some existing “one point” bolt gages include
a built in scope to let you see the echo’s strength. But they still only
not store the zero tension’s entire echo. So how do you tell if the new echo
See the figure to the left and guess which zero crossing (yellow or green
dot) the "one point" bolt gages will use. Answer: The first small peak grew
and will cause the "one point" bolt gages to read far less tension
than is really in the bolt.
See the second echo's distortion in the animation
above. See comparison table.
stores enough information for each bolt to make the reliability
of each measurement much more obvious. SureBolt
uses the familiar Windows 98/2000
user interface to record and play back data.
NASA compares SureBoltTM
to one point bolt gage
Short bolts, weak echo bolts, and bolts that distort the echo when they are
tensioned are unreliable with one-point bolt gages. For example, the CBM Attach
used to hold NASA’s Space Station together
were too short and the echoes were too weak for the one-point bolt gages
to be very reliable. The pressure test, using the "old technology" bolt gages, was difficult. With
it became easy.
On the next
prototype was used on 6 bolts, and it was fully reliable
at all tensions. The
prototype readings were directly compared
to the one-point bolt gage readings for each of the next 5 tests.
the third test, NASA stopped requesting the data from the
one-point bolt gages and relied solely on the
outperformed the one-point bolt gages on every bolt and every test in
reliability and accuracy.
For more details on the technical innovations of SureBolt, see
the comparison table.
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