Method for adjusting swept gain on ultrasonic pulse-echo instruments for uniform sensitivity, irrespective of flaw depth

Abstract

Abstract An overlay is provided for the cathode ray tube screen of an ultrasonic pulse echo flaw detector having a swept gain control. The swept gain control, sometimes called a time-corrected gain control or a distance amplitude-correction gain control, provides for increasing the gain of the receiver system the later flaw echoes are received. By adjusting this gain properly, echoes from flaws of the same size will produce spikes of identical amplitude on the cathode ray tube screen irrespective of flaw depth. The overlay of the invention bears a plot of amplitude versus distance of echoes received from a known echo-producing interface common to a plurality of parts to be tested when the swept gain control is properly adjusted. The common echo-producing interfaces disclosed and preferably used are an interface perpendicular to the path of the ultrasonic waves in the part having a cross sectional area much greater than the cross sectional area of the ultrasonic beam in the part, a large right angle corner, and a cylindrical test hole of known diameter. One method of the invention comprises placing the overlay of the invention on the face of the cathode ray tube display, placing the transducer of the system such that multiple echoes are reflected back and forth between opposing parallel faces of the work piece and adjusting the swept gain until the peaks of the displayed multiple echoes correspond to a plot of the peaks of such echoes on the overlay when the swept gain is properly adjusted. When the plates are to be inspected by an angle beam technique, a Y cut crystal is substituted for the normal X cut crystal to provide the ultrasonic beam perpendicular to the opposed surfaces of the plate. In a second technique disclosed, the angle beam transducer is placed at integral multiples of the half skip distance from the edge of a rectangular work piece whereby the ultrasonic echoes are reflected from the right angle corners thereof and the swept gain is adjusted until the peaks of the spikes of these echoes coincide with a plot on the overlay of the peaks of such echoes at multiples of the half skip distance when the swept gain is properly adjusted. A third method according to the invention comprises placing the angle beam transducer at integral multiples of the half skip distance from a cylindrical hole in the work piece of known diameter and again the swept gain is adjusted until the peaks of the echo pulses received at these half skip intervals correspond to a predetermined curve on the overlay, which indicates the height of the echo spikes as seen on the cathode ray tube when the swept gain is properly adjusted.

Inventors

• 👤 L Niklas

Bibliographic Details