The detection and location of foreign metal objects i n conveyed products

Abstract

The efficiency of materials-processing plants can be seriously affected by the presence of foreign metal objects in the process material. Such objects can arise from machine damage or by contamination before processing begins. The work was originally motivated by a requirement to detect the presence of tramp iron in coal for use in electricity-power generating stations to prevent damage to coal-crushing machinery. There are many other applications, however, in which contamination by metal objects may have serious repercussions. This paper describes an inductive-loop detector apparatus that not only detects the presence of metallic objects but is also able to discriminate between ferrous and non-ferrous objects and to locate the position of the object on both the length and the width of the conveyor belt. This permits ferrous objects to be located within non-ferrous metals and vice-versa, and also makes the removal of the object a relatively simple matter. Details of the loop design are given, together with details of the signal processing required to give the type and position information relating to the foreign metal object. Some results of tests carried out on the laboratory prototype are included at the end of the paper.