An important criterion for the quality or the wear of tubes in industrial applications is the dimensional conformance of the internal diameter over the complete length. Where high demands are made on accuracy, a quick and reliable recording of the data must be ensured, because, for example, wear measurements must be carried out in the chemical
industry on pipes which are already installed, i.e. with the plant shut down. Two pairs of sensors record two tracks offset by 90° in one measurement step.