Radiofrequency sensors for on-line metal tube length measurement

Radiofrequency sensors are suggested and applied for length measurement of elongated metal articles (tubes, rods). According to principles of such sensor design each produced or ready article is considered as one of the conductors of TEM-line. Another elongated conductor (screen) that is parallel to a monitored article is used as the other conductor of such TEM-line. In most cases, section of this TEM-line is excited as resonator with oscillations of basic TEM-type. Resonance frequency of electromagnetic oscillations is used as informative parameter of length sensor. Practically used constructions of length sensors are considered. One of them is determined by a monitored article and metal plane covered by layer of dielectric material. Article is placed on the surface of this layer; periodically disposed dielectric supports may be used instead of continuous plane surface. In the second sensor construction an article serves as inner conductor of coaxial line placed on dielectric supports. Its outer conductor (screen) is longitudinally slotted. Experimental results of length measurements according to the suggested principles are also considered in the paper.