LOW FREQUENCY ELECTROMAGNETIC ANALYSIS OF PRESTRESSED CONCRETE TENSIONING STRANDS

摘要

Discloses apparatus and methods of operation of the apparatus for performing magnetic testing of pre-stressing elements in a pre-stressed concrete cylinder, such as a pipe or water reservoir. The apparatus includes magnetic flux production means disposed proximal to a surface of the cylinde r under test and detector means disposed proximal to a surface of the cylinder in a plane in common with the magnetic flux production means that is orthogonal to an axis of the cylinder. The apparatus operates over a range o f low frequency periodic signals, for example, between 20 and 300 hertz. Output of the inspection apparatus includes analysis providing a multi- frequency plot showing the results of testing a cylinder using two or more frequencies. In accordance with another method of analysis, a single frequency is plotted along with a transformation plot, the transformation pl ot produced by transforming either the in-phase or quadrature components of the received signal in relation to the periodic driving signal by an angle alpha.