Specifications+

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 approaching +-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 the sensitivity.

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.

How repeatable 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.

What about 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.

SureBolt Specs.

MEMORY Over 1,000,000 tension readings on 10" long bolts. 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 Daylight-readable Display with Touchscreen Spill-resistant Keyboard and Touchpad Magnesium Alloy LCD Case and Inner Chassis 13.3" 1024 x 768 (XGA) transmissive, outdoor-readable, anti-reflective TFT Active
BOLT LENGTHS 0.75 to 400⁺ inches Pulse echo mode even on 400 inch bolts.	CPU Mobile Intel® Pentium® 4 Processor-M 1.07 to 1.8GHz featuring Enhanced Intel® SpeedStepTM technology 512KB on-die L2 cache
HELP 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) •30GB HDD
DATA TRANSFER Floppy, Ethernet, RS232, USB, optional CD/RW,	MULTIMEDIA POCKET Holds 1.44MB FDD (standard) • Holds 8X (max) DVD-ROM Drive* (standard)
POWER SUPPLY 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, Auto-sensing/switching worldwide power supply	KEYBOARD & INPUT 87-key with dedicated Windows® key Enhanced pressure sensitive touchpad Touchscreen LCD (with Touchscreen model)
SOFTWARE SureBolt version 2.0.1. Microsoft® Windows® XP/2000 Professional On-Line Reference Manual	INTERFACE Network Interface Card Integrated 10/100 Ethernet Modem Integrated 56Kbps
WARRANTY 1 year limited warranty, parts & labor	PHYSICAL 1.9" (H) x 10.5" (D) x 13" (W) 8 lbs., including battery
CASE 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 prototype was sensitive to as small a change as 0.00001" under ideal conditions. By the way, the current SureBolt is even more sensitive.

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.

Remember, for examples of accuracy, see the discussion above.

I hope this discussion helps.