Checkline TI-MINIMAX - Manual (Page 46)

Dakota Ultrasonics
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8.2 Calibration / Zero misnomer
In the past there have been instances where users were under the impression
that zeroing the unit was the same as calibrating the unit. If the ultrasonic unit
could successfully measure the calibration blocks, the unit was calibrated.
However, this is not the case. The linearity of the unit and material type of the
bolts are not calibrated following a zero procedure. This is a misnomer.
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The MINI-MAX should be sent in for calibration by Dakota Ultrasonics, or
other authorized service representative, on a periodic basis to verify proper
operation of the instrument. Dakota Ultrasonics recommends one-year
intervals.
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Depending on the how critical the application is, bolts should be calibrated in
a lab against a known load prior to measuring. A temperature bath should
also be used to determine the necessary temperature factors required.
The following sections are typical methods of how to perform and calculate a
probe zero using the MINI-MAX. The proper method should be determined by
the level of accuracy required and the specifications and conditions of the
application itself.
8.3 Using a standard bolt
Using any fastener that provides a good ultrasonic echo with both ends ground
and polished can make a simple and effective calibration standard. The primary
objective is to verify a zero value prior to measuring to avoid measurement errors
if the MINI-MAX, transducer, or cable is replaced. While this sounds like an
economic way to go, the user must keep in mind that certified calibration
standards are usually inclusive of an ultrasonic length, velocity, and temperature
coefficient and are certified according to a specific set of standards. The
following procedures outline how to use a standard bolt as follows :
The first step is to setup a group to document our probe zero data. By doing this,
all the values and settings will be saved to the cell location for easy recall at a
later time. This will allow the user to easily verify the zero value and make any
necessary changes to the MINI-MAX, by adjusting the zero value or temperature
depending on the circumstances or conditions.