Chapter 3. Making Measurements
USM Go Operator’s Manual 101
3.13.5 Locks and Error Messages
As long as a valid reference echo is stored, no functions can be changed which could cause an incorrect DGS evaluation. If an attempt is
made to change such a function, the following error message appears:
• “Function Locked - DGS Reference has been recorded”
Likewise, the DGS evaluation must be switched OFF and the reference echo deleted when selecting a new probe (e.g. for a new test
application).
3.13.6 Validity of the DGS Method
Echo amplitude evaluations according to the DGS method are only reliable and reproducible in cases when:
• The reference echo is received from the test object if possible. If this is not possible, it should be verified that the reference block is made
of the same material as the test object.
• The evaluation is carried out using the same probe which was also used for recording the reference echo. Another probe of the same type
can be used only after recording a new reference echo.
• Echo amplitudes for reflector distances smaller than half of the probe near-field length are subject to extreme variation, for physical
reasons due to interference phenomena effecting the area. Thus, evaluation results may fluctuate more than the usually permissible
±2 dB. An evaluation according to the DGS method is possible, but it is not recommended in such a case.
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