910-269-EN, Rev. B, June 2011
146 Chapter 9
Due to the acoustic characteristics of dual transducers, nonlinearity in the
distance calibration occurs as the thickness of the material decreases. The point of
maximum sensitivity is determined by the roof angle of the particular dual
transducer. It is recommended that the distance calibration is carried out using a
step block that covers the range of interest. Be careful when interpreting thickness
measurement readings made outside the calibrated range. The EPOCH 1000
Series does not have v-path correction; therefore, there might be some
nonlinearity within the calibrated range depending on the minimum thickness
used in the calibration process.
The zero offset value of dual element transducers can vary significantly at extreme
temperatures. If the temperature changes more than a few degrees from the
temperature at which the zero offset value was established, recheck its value. If
thickness measurements are to be made over a wide temperature range, it is strongly
recommended to use Olympus dual transducers that are designed for high-
temperature applications and that have built-in delay lines with a stable sound
velocity that does not change significantly with temperature. Specific
recommendations are Olympus D790-SM and D791 dual element transducers.
To calibrate using a dual element transducer
1. Follow the initial setup procedure outlined in section 9.1 on page 134.
2. Connect the transducer to an appropriate cable, and then connect the cable to the
conventional transducer connectors at the top of the instrument.
3. Select 1/5 > Pulser > Mode = Dual.
4. Press [GAIN], and then adjust the value very high so that the leading edges of the
back-wall echoes appear as nearly vertical lines on the screen.
5. To use the leading edge when making thickness measurements, set the
measurement gate(s) to the edge detection mode:
a) Choose 2/5 > Gate Setup > Setup to open the Gates setup page.
b) In the setup page, highlight Gate<n> Measurement Mode and set its value to
Edge.
c) Press [ESCAPE] to exit the setup page.
6. Select 1/5 > Auto CAL > CAL Mode = Thickness.
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