An Experimental Study of Magnetic Field Coupling from Proximity Detection Systems to Trailing Cables

Some of the common and serious hazards in underground mines are the dangers of being pinned, crushed, or struck by a large mining machine such as a scoop or a continuous mining machine (CMM). Proximity detection systems (PDSs) have been applied to protect miners from these hazards. The primary components of PDSs that are currently approved by the Mine Safety and Health Administration (MSHA) for use in underground coal mines are machine-mounted magnetic field generators and a miner wearable component (MWC) which measures the strength of the magnetic fields produced by the generators to determine distance from the machine. Since these systems are magnetic-field-based, they can be adversely impacted by nearby cables due to parasitic coupling. Some mining equipment in underground mines is electrically powered by long trailing cables that are pulled through the mine behind the equipment. Because the components of the PDS (generators and MWC) are frequently in close proximity to these cables, parasitic coupling can occur. Researchers from the National Institute for Occupational Safety and Health (NIOSH) investigated the influence of trailing cables on the performance of PDSs. In particular, a three-phase model was proposed to describe the coupling process. The factors for controlling the magnetic field coupled from a field generator to a trailing cable were experimentally studied. The results show that the coupling is primarily controlled by two factors: the distance between the PDS components and the cable, and the impedance between the cable and the ground. The coupling can be mitigated by either maintaining some minimum separation distance between the PDS components and the cable or increasing the impedance between the cable and the ground. The results presented in this paper can help PDS manufacturers to design systems that are more immune to these effects.