910-269-EN, Rev. B, June 2011
Glossary 325
Decibel (dB) A unit which compares levels of power. Two power levels
P1 and P2, are said to differ by n decibels when: n = 10
log
10
This unit is often used to express sound intensities. In this
case, P2 is the intensity of the sound under consideration
and P1 is the intensity the reference level.
Delay control Subcircuit of the sweep generator that allows a variably
adjustable time period from the sending of the trigger
pulse to the start of the sweep across the data display.
Detectability The ability of a test system (instrument and transducer) to
detect or “see” a given size reflector. This is also known as
“sensitivity.”
Distance amplitude
correction (DAC)
A method of flaw evaluation that uses a test block with a
known size reflector at varying known distances from the
transducer. This allows you to plot a curve on the data
display that represents the amplitude of that size reflector
throughout a given distance range. This curve
compensates for the loss of energy due to beam spreading
and attenuation.
Dual element probe A probe containing two piezoelectric elements, one which
transmits and one which receives.
Dynamic range The ratio of maximum to minimum reflective areas that
can be distinguished on the data display (usually based on
decibel ratios).
First critical angle The minimum incident angle in the first medium at which
the refracted longitudinal wave is eliminated from the test
specimen.
Flaw A discontinuity that may be undesirable but does not
necessarily call for rejection.
Frequency The number of complete cycles undergone or produced by
an oscillating body.
Table 37 Glossary (continued)
Term Definition
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