Uncertainty in ultrasonic thickness measurements based on the spacing between the first and second bottom-reflected signals. II. rough bottom surface. irregularities with rectangular profiles

摘要

The uncertainty in ultrasonic thickness measurements as a function of the depth R{sub}(m.b) of a rough layer on the bottom surface of a tested object based on measurements of the separation between the first and second bottom-reflected pulses (more briefly, h{sub}12-method) has been investigated. The simplest model of the rough layer, i.e., a layer with rectangular profiles of juts, has been analyzed. The function △h{sub}l2(R{sub}(m.b)) has been obtained theoretically and tested in experiments. The h{sub}12 -method of thickness measurement has been compared with the h{sub}1-method for objects with rough surfaces. As in the case of the h{sub}1-method, a critical range of R{sub}(m.b) has been discovered, where the measurements by ultrasonic thickness gauges are unstable, the amplitudes of the first and second bottom-reflected signals are minimal, the uncertainty △h{sub}12 has the maximal absolute value, has a jump, and changes its sign. The width of this critical range is less than in the case of the input surface. The theoretical conclusions are supported by experimental data.