Measurement of lay length of wire rope

An apparatus for measuring lay length of a wire rope having a number of spirally wound external strands with grooves between the strands causing the wire rope to have a spirally grooved outer surface undulating in surface height from a central axis of the wire rope, and having lay length over which each of the strands completes a single circumferential spiral path around the wire rope, the apparatus comprising:

• a sensor device having a sensor body defining an elongated passageway enabling the wire rope to be advanced therethrough in a direction of the central axis of the wire rope while permitting limited lateral movements of the wire rope, the sensor device having one or more generators of magnetic flux positioned to create a magnetic flux circuit having a part thereof passing through a region of the wire rope when present in the passageway;
• sensors on the body capable of sensing changes of magnetic field strength or magnetic flux in said region of the rope caused by variations of proximity of the wire rope to the sensors, the sensors being located at two or more positions spaced circumferentially around the passageway, the sensors generating signals corresponding to said changes sensed at the two or more positions, such that the signals each include components due to surface height and components due to lateral movements of the wire rope at said positions;
• means for subtractively combining the signals from the sensors at the at least two positions to eliminate the components due to the lateral movements to produce a combined signal having an oscillating pattern caused by surface height of the wire rope;
• means for associating oscillations in the oscillating pattern with physical distances along the wire rope;
• and
• a lay length calculator or display that calculates or displays a distance along the wire rope of a plurality of the oscillations corresponding in number to the number of spirally wound external strands of the wire rope.

A sensor device for measuring lay length of a wire rope, the device comprising:

• a sensor body defining a passageway enabling a wire rope to be advanced therethrough in a direction of a central axis of the wire rope while permitting limited lateral movements of the wire rope;
• one or more generators of magnetic flux within the sensor body positioned to create a magnetic flux circuit having a part thereof passing through a region of a wire rope when present in the passageway;
• and
• a plurality of sensors on said body arranged around said elongated passageway, said sensors capable of sensing changes of magnetic field strength or magnetic flux in the region of a wire rope in said passageway caused by variations of proximity of the wire rope to the sensors and of generating signals corresponding to said sensed changes;
• wherein the sensors are located at positions spaced circumferentially around the passageway and are interconnected to form two groups of sensors with the sensors of the first group alternating in position around the passageway with sensors of the second group, and with the sensors of the first group interconnected to generate signals that are added together and the sensors of the second group interconnected to generate signals that are added together.