USE OF ST-21I THICKNESS GAUGES FOR THE INSPECTION OF PIPE COATINGS.

The ST-21I instrument was designed for inspecting dielectric materials from 2 to 16 mm in thickness. Its action is based on measuring the relative reflection coefficient of an electromagnetic wave from a quasiplane dielectric layer by a method of comparing the reflected wave with a reference signal. The comparison of the signals is made in an amplitude-phase discriminator, which provides the maximum sensitivity of the method in inspecting the thickness of dielectrics on a metal base. In inspecting dielectrics with low dielectric losses and a thickness of less than 1 mm damping of the radio wave in the material by the ST-21I instrument is negligible. Measurements using this instrument may be made solely by the phase method, i. e. , by the method of comparing the phase of the signal reflected from the metal base with the reference signal. 4 refs.