DMTA-10022-01EN, Rev. C, January 2015
Software Options
75
In some cases, an error can occur if you are using a D790 transducer to measure
thicknesses above 18 mm (0.7 in.). Typically, this error is due to a mode-converted
shear-wave echo that may appear before the second back-wall echo. If this unwanted
echo is larger than the second back-wall echo, the gage measures the distance to it,
which produces a thinner reading.
You can usually distinguish the unwanted shear-wave echo from the correct back-wall
echo by examining the waveform display. The distance between the first and the
second back-wall echoes is the same as the distance between the zero thickness point
and the first back-wall echo. If there is an echo between the first two back-wall echoes,
it is probably a mode-converted shear-wave echo. Use the manual echo-to-echo
detection mode techniques, and manually adjust the E1 blank to eliminate this error
(see “Blanking Adjustments in Manual Echo-to-Echo Detection Mode” on page 73).
Using the D797 transducer beyond 18 mm (0.7 in.) helps eliminate the possibility of
this error.
In some cases, the second or third back-wall echo is smaller in amplitude than
subsequent echoes, which causes the instrument to give a double or triple reading. If
you are using a D790 transducer, this effect may occur around 5 mm (0.2 in.) on flat,
smooth steel samples. If this occurs, it is clearly visible on the waveform display, and
you can work around it using the manual Echo-to-Echo detection mode, or by moving
the extended blank beyond the previously detected first echo.
When the 45MG cannot make an echo-to-echo reading, the
LOS
flag appears on the
screen. In this case, the waveform display shows that either no echoes are large
enough to be detected, or that only one echo is detectable. In the latter case, the Echo-
to-Echo detection bar begins at the detected echo, but extends indefinitely to the right.
Table 4 Recommended transducers for various steel thickness ranges
Transducer type
Thickness range
a
a.
Thickness ranges are dependent on the transducer type, material
conditions, and temperature.
D798
1.5 mm to 7.6 mm (0.060 in. to 0.300 in.)
D790/791
2.5 mm to 51 mm (0.100 in. to 2.00 in.)
D797
12.7 mm to 127 mm (0.500 in. to 5.00 in.)
D7906
2.5 mm to 51 mm (0.100 in. to 2.00 in.)
Summary of Contents for 45MG
Page 8: ...DMTA 10022 01EN Rev C January 2015 Table of Contents viii List of Tables 227 Index 229...
Page 26: ...DMTA 10022 01EN Rev C January 2015 Introduction 16...
Page 36: ...DMTA 10022 01EN Rev C January 2015 Chapter 1 26...
Page 42: ...DMTA 10022 01EN Rev C January 2015 Chapter 2 32...
Page 136: ...DMTA 10022 01EN Rev C January 2015 Chapter 6 126...
Page 150: ...DMTA 10022 01EN Rev C January 2015 Chapter 7 140...
Page 157: ...DMTA 10022 01EN Rev C January 2015 Configuring the Instrument 147 Figure 8 3 The COMM screen...
Page 158: ...DMTA 10022 01EN Rev C January 2015 Chapter 8 148...
Page 196: ...DMTA 10022 01EN Rev C January 2015 Chapter 10 186...
Page 208: ...DMTA 10022 01EN Rev C January 2015 Chapter 11 198...
Page 226: ...DMTA 10022 01EN Rev C January 2015 Appendix A 216...
Page 232: ...DMTA 10022 01EN Rev C January 2015 Appendix C 222...
