# BASICS OF ACOUSTICS: Groups of controlled parameters 2

6.4 Fourth group of parameters: time selection zone – control zone
To the parameters of the time selection zone (zone BS or strobe BS) can include the beginning, duration and end. The dimension of the BC zone can be expressed in three variants: distance along the ray (R), height (Y), time (T). The beginning and end of the aircraft zone should correspond to the boundaries of the control zone. Depending on the method used (echo or mirror-shadow), the zones of the aircraft may differ. When using the echo method, exceeding the threshold by a signal in the strobe will be accompanied by a light signalling “defect”, for a mirror-shadow method, on the contrary, a decrease in the signal (bottom) will show a “defect”.

Fig.7.2 – Time selection zone (SI-strobe impulse) and control zone (CZ)

6.5 The fifth group of parameters: the sensitivity of the equipment – the sensitivity of the method
Sensitivity as an instrument parameter is measured in dB, since in this case it is understood as the minimum possible signal that has exceeded the threshold. The conditional sensitivity is determined by the state standard sample СB-2, СB-3Р in the amplitude of the echo-pulse from the standard reflector (Fig.7.3)
Real sensitivity is the minimum size of a defect of a certain type, the type detected in the CO at a given depth.
Limit sensitivity is the minimum size of an ideal reflector of a certain type of species, detected in the CO at a given depth. Of all types of sensitivities, the limiting sensitivity is the minimum size.

Angle beam probe

Fig.7.3 – Finding the conditional sensitivity

Equivalent sensitivity is the minimum size of an artificial reflector or a real defect that is detected in the OK at a given depth. As an artificial reflector, various models of defects can be used: sawing, drilling, segment, cutting, etc.

Fig.7.3 – Finding the equivalent sensitivity