Magnetic measurement for magnet load assessment

One of the problems encountered with lifting magnets which use either permanent- or electromagnets is uncertainty about the security of load attachment. If the attachment force is only slightly greater than the weight of the load then any acceleration or disturbance of the load can threaten its continued attachment. A system has been developed, primarily for use with permanent magnet lifts, but applicable to electromagnets also, for assessment of the load security before the load leaves the ground. A flux integrator fed by a sensing coil is used to sense the attachment force of a magnet to its load and this figure is compared with the growing force in the lifting attachment, sensed during initiation of a lift, by means of a load cell inserted in the hoist coupling. Any predetermined safety factor can be imposed so that if lifting force exceeds a set percentage of attachment force an alarm signal is given or the hoisting motor may be automatically inhibited.