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Note: A convenient way to perform the above Load Factor calculations is to use the
bolt calculator included in the DakView PC software.
It's important to note that performing the calculations above is only a good
approximation at best. In all cases, if possible, a field calibration should be
performed if the user intends to perform measurements in terms of load.
11.2 Calibrating Load Factor (Field Calibration)
Clearly, the most effective way of calibrating the load factor is by performing a field
calibration. Often times, material constants are unknown or cannot be calibrated in a
laboratory environment. In cases such as these, a field calibration is the most
accurate means of calibration. A field calibration is accomplished using a tensile
tester, load cell, or other calibrated load device to compare known loads against
ultrasonic elongations. The MAX II is equipped with a self- calibrating feature that
uses a linear regression or vector equation to produce a best-fit line through the
known loads, minimizing error.
The result is an added load offset (intercept), in the case of regression, and a load
factor (slope) to correct the ultrasonic measurements to the known loads. The
regression produces a load offset and load factor, while the vector sets the offset to
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L
C
D
E
L
X
Effective Length
GlobalTestSupply
www.
MAX II Bolt Tension Monitor
C LA M P LE N G T H
E FFE C T IV E LE N G T H
C L A M P L E N G T H
E F F E C T IV E L E N G T H
L
= Average length under stress
E
C
= Clamp length
L
D
= Additional diameter added for head, nut(s),
X
and or blind hole.
89
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