Detector bank distinguishes band join from metallic foreign objects - using sensors in line coupled to adder with discriminating logic to decide whether object or join occurs

摘要

A bank of sensors located above fabric strip fed at high speed detects the presence of any small metallic objects e.g. needles that are likely to result in damage to process rollers. The sensing head consists of a number of individual stages (7-13) each generating an electrical output signal when a metallic object passes on the fabric (23). The width of each sensor is selected such that the width of two sensors is less than the minimum band width. Outputs from sensors are coupled to an adder (22) with an amplitude detector (25) on the output. A logic circuit (28) generates two outputs; one of which (30) is present alone if less than two sensors are actuated, thus indicating a foreign object. If both outputs (29, 30) are present a form in the band is indicated.