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Dakota Ultrasonics
12) Calculate the value of the Sonic Stress Factor at each load on each sample
bolt.
SSF
B
1
L
1
13) Determine the average value of the Sonic Stress Factor by dividing the sum
of all SSF values divided by the total number of SSF values.
10.4 Temperature Factor Calibration
The thermal expansion of the fastener and the ultrasonic velocity change with
temperature are two separate effects. However, for the purpose of the MAX II they
are combined into a single factor known as the Temperature Factor. The important
thing to note is that both the thermal expansion and the velocity are changing with
respect to changes in temperature. The MAX II always measures a fastener at 68
F. If the temperature of the fastener is currently being measured at 108 F, the MAX
II will compensate, or correct, the measurement back to 68 F. Note: This is an
arbitrary temperature range only. The primary thing to consider is to use a
respectable temperature range with at least 5 different temperature points. The
following procedure outlines the process for experimental determination of the
Temperature Factor for a bolt made of a specific material type and geometry.
Required Equipment.
A means of varying and measuring the temperature of the sample bolts
between 48 to 108 F to an accuracy of +/- 2 F. The device must allow
for a transducer to be connected to one end of the bolt for the purpose of
measuring.
Many sophisticate temperature chambers are commercially available, and
ideally suited for this function. However, a simple and inexpensive
method can be achieved by immersion of the sample bolts in a water
bath, which can be heated to boiling or cooled by adding ice. At sea level
this will reliably vary the bolt temperature between approximately 48 to
108 F depending on water purity and atmospheric pressure. By
measuring the temperature of the stirred water bath with a precise
mercury thermometer, while reading the ultrasonic length of the bolt,
accurate calibration points can be obtained.
A Dakota Ultrasonics MAX II Ultrasonic Bolt Tension Monitor.
L
L
L
M
1
M
0
SSF
B
1
L
2
L
L
L
U
1
U
0
L
L
M
2
M
0
M
SSF
B
1
L
3
L
L
U
2
U
0
U
106
L
3
M
0
L
3
U
0
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