Electromagnetic Method of Testing the Wire Rope Vis-a-vis Calibration of Defects

This paper presents the details about calibration of defects; wear and broken wires by electromagnetic method in a wire rope used for hoisting of men and material in mines, aerial rope ways, lifts etc. Electromagnetic method of testing the wire ropes consists of powerful magnets to magnetize the wire rope, and sensors to detect the defects in the wire ropes. A typical instrument used in the investigation consists of the inner coil to detect the local defects like corrosion, pitting, broken wire, wear and nicks. Outer coil (Hall sensor) detects the loss in metallic area. The major problem in analyzing the defects is due to the presence of the noise generated due to construction of the wire rope, which interferes with the signals due to the defects. Outer coil (LMA) signals are easy to analyse, as the shift in voltage from the base line is easily correlated with the loss in area calibrated using calibration rod before recording the test data. The difficulty arises in analyzing the inner coil signals, which detects the signals from wear, nicks and broken wire, which cannot be distinguished if they are of the same magnitude. In the present study a method was adopted to simulate the magnitude of the defect signals of wear and broken wear by creating artificially in the laboratory, which can be used for analyzing the actual signals recorded during in-situ testing on wire ropes.