Material Sound Velocity And The Zero Calibrations - Olympus 45MG User Manual

The frequency at which you perform a transducer zero-compensation procedure
depends on the rate of change of the internal temperature of the dual element
transducer. This is related to the material surface temperature, the frequency of
transducer application, the length of time the transducer is held in contact with the
material, and the accuracy that you want to obtain.
NOTE
When measurements are made on surfaces that are significantly above room
temperature, the zero point should be recalibrated on a regular basis. This is less
important for transducers with part numbers D790-SM, D791-RM, D797-SM, and
D798 than for other transducers with various types of resin delay lines.
For high-temperature measurements, Olympus recommends developing a transducer
zero-compensation schedule that takes these factors into account. For example, use
the D790-SM, D791-RM, or D797-SM for high-temperature applications, thereby
minimizing the frequency of the zero compensation. The D790-SM and D791-RM can
also be used for general-purpose applications.
5.2.4

Material Sound Velocity and the Zero Calibrations

The 45MG performs a calibration doubling verification to help prevent mis-
calibration on thin samples. Doubling occurs when the instrument measures the time
of flight to the second back-wall echo rather than measuring the time of flight to the
first back-wall echo. The 45MG compares the measured time of flight to the expected
time of flight based on the current sound velocity. The 45MG displays a warning
message if doubling is suspected. Doubling can occur when measuring a thickness
that is below the minimum range of the transducer, or when using a transducer that is
worn out, or getting low in sensitivity.
NOTE
You can also achieve a material sound velocity and zero calibration procedure by
performing the operations in the reverse order, starting with the zero calibration,
followed by the material sound velocity calibration.
DMTA-10022-01EN, Rev. C, January 2015
Basic Operation 59