Dakota Ultrasonics MINI--MAX - Manual (Page 105)

MINI-MAX Ultrasonic Bolt Tension Monitor
99
The important thing to note is that both the thermal expansion and the velocity
are changing with respect to changes in temperature. The MINI-MAX always
measures a fastener at 68
° F. If the temperature of the fastener is currently
being measured at 108
° F, the MINI-MAX 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 MINI-MAX Ultrasonic Bolt Tension Monitor.
• A minimum of three sample bolts, which are representative of the bolt
type and geometry for which the Temperature Factor is to be
determined.
NOTES:
• The Dakota Ultrasonics MINI-MAX must be calibrated, or zeroed, as
described in the procedure entitled Measuring System Zero in Chapter 8.
• The sample bolts should be left to soak at the measured temperature points
for a period of not less than 20 minutes, to insure that temperature is uniform
throughout the sample.
• If a water bath is used, care must be taken to avoid immersion of the
ultrasonic transducer.