Dakota Ultrasonics MX-1 - Manual (Page 16)

Dakota Ultrasonics
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At this point, the MX-1 has successfully calculated it's internal error
factor, and will compensate for this value in any subsequent
measurements. When performing a "probe-zero", the MX-1 will always use
the sound-velocity value of the built-in probe-disc, even if some other
velocity value has been entered for making actual measurements. Thoug h
the MX-1 will remember the last "probe-zero" performed, it is generally a
good idea to perform a "probe-zero" whenever the gauge is turned on, as
well as any time a different transducer is used. This will ensure that the
instrument is always correctly zeroed.
Calibration
In order for the MX-1 to make accurate measurements, it must be set to
the correct sound-velocity for the material being measured. Different types
of material have different inherent sound-velocities. For example, the
velocity of sound through steel is about 0.233 inches-per-microsecond,
versus that of aluminum, which is about 0.248 inches-per-microsecond. If
the gauge is not set to the correct sound-velocity, all of the measurements
the gauge makes will be erroneous by some fixed percentage.
Programming the Sound Velocity
Since the MX-1 is a fixed velocity gauge, the correct sound velocity for
the material being measured must be programmed into the gauge via the
serial port on the bottom of the unit. Approximate sound velocities for
common materials can be found in appendix C.