Quotes from "An Introduction To
The Design And Behavior Of Bolted Joints (3rd ed. by
John Bickford) Probably the best bolted
joint resource available. No
affiliation with SureBolt or FAST-DAQ. He is
discussing ultrasonic bolt gages in general.
(pg 403) ... As a result, we feel that the
equipment is capable of residual preload measurements with an accuracy
+-5% in most field situations, and can approach +-2% in laboratory work.
There are even well-documented examples where +-1% was achieved
consistently in aerospace applications; but ...
How sensitive is SureBolt to changes
in bolt tension? How about +- 25 lbs
tension (0.25 inch diameter bolt that is
only 2 inches long, and has a preload tension of 3500 lbs).
These bolts were considered impossible for other bolt gages due to
their cupped heads and weak signals (.02
volts). But, this +- 25 lbs tension was
achieved under under ideal
conditions (the transducer was not moved,
and the temperature was not changing).
SureBolt even allows you to increase the sensitivity, by
increasing the number of seconds SureBolt averages the data. In
the above example, the +- 25 lbs could
easily be +- 10 lbs (if the number of
seconds for averaging is increased to 10 seconds).
One application had a sensitivity of
better than +- 600 lbs in a load of 6,000,000 lbs
(their studs were 15 inches in diameter and 24 feet
long). See how the application determines
Warning, this question is about sensitivity and
resolution, not accuracy. Many manufacturers' specs only tell you
how many digits their bolt gage displays. The number of digits is
not accuracy and may not even be a good indication of sensitivity.
is SureBolt if I have to remove and
replace the transducer between the tension readings? This
is called a gage R&R study
(130kB Word file). Another
manufacturer who was familiar with bolt gages, did this
gage R&R and sent us the
results. First, they told us how to take
the R&R measurements. Second, they asked us to send them the raw
data. Finally, they ran it through their industry standard
statistics program and sent us the results.
Results: The bolt was tensioned to 10,000 lbs.
The Gage R&R said that one standard deviation was 32.286 lbs.
Read the email that accompanied the report.
ACCURACY? Accuracy depends on
the application. See John Bickford's
quote above. 5% is pretty easy. 2% requires careful use and
controlled conditions. The longer the
bolt's grip length, the better accuracy (if temperature change
is not a factor). With SureBolt, it is
much easier to take careful measurements and verify the user
recorded good echoes. Let me give you three extreme examples:
1) NASA had some 0.75 inch grip length
bolts and wanted the most accurate readings possible. (0.25 inch diameter with cupped
heads which gave very weak signals). Using
SureBolt, separate stretch coefficients were experimentally derived for
each bolt and nut combination. This gave repeatable accuracies
to about 2% (under laboratory conditions). Without SureBolt it
was impossible to get reliable measurements on so short a bolt
with a cupped head.
2) NASA wanted to tension their new 10 inch long
X-33 hold-down bolts to within 2%. The calibration tension
machines were only accurate to 3%. The SureBolt prototype was
more accurate than that!
3) A customer wanted to preload bolts that
were 240 inches long. SureBolt measured tension changes to better than 0.1%
full scale. However, calibration coefficients better than 5%
were not available for 15 inch diameter
bolts tensioned to 6,000,000 lbs. Does
anyone have a load cell for 6 million lbs?
Note: User errors are typically the limiting
factor when measuring bolt tensions. SureBolt
uses a patented "whole echo" method to dramatically increase
reliability and minimize user errors.
Over 1,000,000 tension readings on 10" long
Shorter bolts take less memory.
Over 2,000,000 tension readings on 5" bolts. Limited only by
the built-in hard disc.
Bolt groups. Over 1,000,000
Display with Touchscreen
Keyboard and Touchpad
Magnesium Alloy LCD Case and Inner Chassis
13.3" 1024 x 768 (XGA)
transmissive, outdoor-readable, anti-reflective TFT Active
0.75 to 400+ inches
Pulse echo mode even on 400 inch bolts.
Mobile Intel® Pentium® 4 Processor-M 1.07 to
Enhanced Intel® SpeedStepTM technology
512KB on-die L2 cache
Online help screens.
Built-in SureBolt web pages for tutorials online.
Video tutorials installed (standard)
STORAGE & MEMORY
256MB SDRAM (DDR) standard, expandable to 768MB
(PC-2100 memory is required)
Floppy, Ethernet, RS232, USB, optional CD/RW,
Holds 1.44MB FDD (standard)
• Holds 8X
(max) DVD-ROM Drive* (standard)
Lithium Ion rechargeable battery pack (11.1V, 3.6Ah)
Battery operation: up to 1.5 hours (with first
battery). Optional battery pad: up to 7 hours.
AC Adapter: AC 100V-240V 50/60Hz,
worldwide power supply
KEYBOARD & INPUT
87-key with dedicated Windows® key
Enhanced pressure sensitive touchpad
Touchscreen LCD (with Touchscreen model)
SureBolt version 2.0.1.
Microsoft® Windows® XP/2000 Professional
On-Line Reference Manual
Network Interface Card Integrated 10/100 Ethernet
Modem Integrated 56Kbps
1 year limited warranty, parts & labor
PHYSICAL 1.9" (H) x 10.5" (D) x 13" (W)
8 lbs., including battery
Pelican Computer+ case for travel and storage of
your SureBolt, transducers, cables, etc.
What is the most important
specification? How accurate is the bolt
gage to changes in bolt tension! Since most engineers think in terms of
bolt elongation, this
tension change is directly related to a change in bolt length. Bolt
gages often give their specs in terms of change, i.e. inches. So, what are
some of the competing bolt gage specs? Our search
indicated that no other bolt gage manufacturers provide an accuracy
specification or an example of accuracy for an application:
Company #1 = 0.0010 to 0.00001 "Digital Resolution"
(I guess you set the display to show the resolution you want.)
Company #2 = no stated resolution
Company #3 = 0.0001" resolution.
You take this value ,then you pull out your engineering books and
look at the Stress versus Strain, and determine the Stress accuracy.
Right? No! Just because a display shows you
0.00001 in resolution does not mean it is accurate to 0.00001 inches.
SureBolt is far more sensitive to changes in tension than any other
bolt gage because of the patented "Whole Echo" method. BUT, resolution
and sensitivity are NOT the same as ACCURACY!
Let me explain by using an additional real life example. NASA wanted to use
an ultrasonic bolt gage on their short (2 inches
long), 1/4 inch diameter Space Station
bolts. (Previously impossible for other bolt gages
because the bolt head had a indention that left a very weak signal. No
problem for SureBolt.) NASA engineers only wanted
to see the change in bolt tension as an adjacent bolt was tightened.
These conditions were ideal for using ultrasonics.
So, under ideal conditions (no transducer movements
and insignificant temperature changes), SureBolt could detect
less than 25 pounds change in tension on a 3500 Lb preloaded bolt. That
translates to a change in only 0.00001" . Wow, you mean SureBolt is
accurate to within 0.00001" ? NO! The SureBolt
sensitive to as small a change as 0.00001" under ideal
conditions. By the way, the current SureBolt is even more
In fact, SureBolt shows you enough "Digital Resolution" to
claim 0.000002" resolution, but just because the display can show
that kind of digital resolution does not mean you can use it.
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