Apparatus and method of damage detection for magnetically permeable members

An apparatus to detect faults in a plurality of magnetically permeable reinforcing cable members of a conveyor belt, where said belt comprises a main body portion having upper and lower surfaces, a longitudinal axis, a transverse axis, and a vertical axis, and said reinforcing members are longitudinally aligned and positioned with the main body portion at spaced intervals along the transverse axis of the belt, said method comprising:

• a. magnetic field means comprising forward, rear and middle armature portions to provide a longitudinally aligned magnetic field at an operating location adjacent to one of the surfaces of the belt;
• b. mounting means to position said magnetic field means so that with relative movement of said belt and said magnetic field means in a manner that said belt moves longitudinally and forwardly relative to said magnetic field means, the cable members are passing through the magnetic field;
• c. said magnetic field means being arranged to provide a first forward field component and a second rear field component, with said first and second field components being longitudinally spaced and longitudinally aligned, with said forward field component extending from the forward armature portion through, and proximate to, adjacent forward portions of the cable members to the middle armature portion, and with said rear field component extending from the rear armature portion through, and proximate to, adjacent rear porions of the cable members to the middle armature portion, said first and second magnetic field components being constant, with the first and second magnetic field components being aligned and in the same longitudinal direction, said magnetic field means being positioned and arranged so that with the armature similarly spaced and positioned relative to the belt, and with the forward and rear cable portions having substantially equal reluctance paths relative to the first and second field components, flux fields of the first and second field components passing through the first and second cable portions and adjacent thereto are substantially similar and of equal intensity, and in the same direction, and with the reluctance paths of the forward and rear adjacent cable portions having different reluctance paths, magnetic flux field portions of the first and second field components through the first and second cable portions differ from one another and magnetic flux field portions of the first and second field components adjacent to and outside of the belts, and also spaced away from the cables within the belt, differ from one another;
• d. a plurality of sensors capable of responding to absolute field strength, regardless of variations in field strengths, positioned at transversely spaced locations in said magnetic field adjacent to said conveyor belt to respond to differences in absolute field strength of first and second field portions of said first and second field components at a location outside of said belt and spaced from the cables;
• e. monitoring means to monitor each of said sensors to respond to relative absolute field strengths of said first and second field components to ascertain relative difference in said first and second field portions to detect a situation where a cable fault passing from a location of said front armature portion to said middle armature portion causes a change in flux field intensity of said first field portion, and said cable fault passing from said middle armature portion to said rear armature portion causes a change in flux field intensity of said second field portion, by detecting an imbalance between field intensities of said first and second field portions;
• whereby an imbalance of said first and second field components can be detected, even during periods when there is no variation in field intensity of said first and second field components and when said belt is moving toward and away from said sensors.