1.2.7
Calibrated Gain Control (Attenuator)
Circuitry with which gain can be reduced finite amounts by switching
electrical signal attenuation into the circuit.
1.2.8
Process of comparing an instrument or device with a standard to determine
accuracy or produce a scale.
1.2.9
Cathode Ray Tube (CRT)
An electron tube in which a controlled beam of electrons from the cathode
is used to produce an image on a fluorescent screen at the end of the tube.
1.2.10
Couplant
Any material, usually a liquid or semiliquid, used between the search unit
and the inspection surface to exclude air and to convey the ultrasonic
vibrations between the search unit and the material being inspected.
1.2.11
Damping Control
Control that varies the duration of transducer ringing.
1.2.12
Decibel (dB)
Units for the logarithmic expression of the ratio of power levels. Power
levels can be functions of voltage, current, or impedance, for example.
Decibel units having no values of their own are only significant when a
reference is stated, as 10 dB above one reference level or 6 dB below
another reference level.
1.2.13
Delay Control
Means of delaying the pattern obtained on the CRT.
1.2.14
Discontinuity
Anything within a material that will cause a detectable interruption in an
ultrasonic beam.
1.2.15
Distance-Amplitude Correction Curve
Curve showing the relationship between signal amplitude and equal-sized
reflecting surfaces at various distances from the transducer. Reference
standards are used to obtain such curves.
1.2.16
Dynamic Range
Ratio of maximum to minimum size of reflective areas that can be adequately
distinguished on the CRT at a constant gain setting.
1.2.17
Effective Depth of Penetration
Maximum depth at which the sensitivity is satisfactory for the quality of
test desired.
SECTION 05091A
Page 6
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