Appendix C – Glossary
Part # 910-250C
167
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
CRT screen 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 cathode ray tube
(usually based on decibel ratios).
Electronic Zero The point in time when the pulser fires the initial pulse
to the transducer and the point on the cathode ray tube
screen where the electron beam leaves the baseline due
to the initial pulse signal coming from the transmitter.
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 in one second.
Gain Used in electronics with reference to an increase in
signal power; usually expressed as the ratio of the
output power (for example, of an amplifier) to the input
power in decibels.
Gain (Control) Selects the amount of calibrated gain (dB) available
within the instrument. Usually consists of a coarse gain
control (additions at 20 dB increments), and a fine gain
(additions at 1 or 2 dB increments).
Gate An electronic baseline display used to electronically
monitor portions of the displayed range with reference
to distance or amplitude.
Term Definition
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