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Preface
Ultrasonic Thickness Measurement Critical Operating Procedures (cont.)
6. Doubling
Ultrasonic thickness gauges will, under certain conditions, display readings which are twice (or in some cases, three times) the actual
material thickness being measured. This effect, commonly known as "doubling," can occur below the minimum specified range of the
transducer. If the transducer being used is worn, doubling is possible at a thickness greater than the minimum of the specified range.
When using a new transducer, any reading which is less than twice the minimum specified range of the transducer may be a "doubled"
reading, and the thickness of the material being tested should be verified by the use of other methods. If the transducer shows any sign of
wear, doubling may occur at a second echo, or other echo signal combinations may produce a readable signal. The instrument reading and
apparent thickness are up to about twice the actual value, resulting in a thickness greater than twice the minimum of the specified range.
This thickness should be determined by calibrating the instrument/transducer combination on reference blocks that represent the complete
range of possible thicknesses that may be encountered in testing. This is particularly important when a test piece is being ultrasonically
measured for the first time or in any case where the history of thickness of the test specimen is unknown.
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DM5E Operating Manual
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