Modeling the Influence of Steel Mesh on Magnetic Proximity Detection Systems (PDSs) in Underground Coal Mines

To protect miners from pinning, crushing, and striking injuries, the Mine Safety and Health Administration (MSHA) published a final rule in 2015 requiring underground coal mine operators to equip continuous mining machines (CMMs), except full-face CMMs, with proximity detection systems (PDSs). Currently all MSHA-approved PDSs are magnetic PDSs which can be affected by the presence of steel mesh that is commonly used in underground coal mines. In this paper, the influence of steel mesh on the performance of magnetic PDSs is investigated based on FEKO simulations. Particularly, we present a ferrite rod antenna model based on the parameters of an actual antenna used in a commercial PDS. We first validated the FEKO antenna model by showing that the simulated magnetic fields match well with the measured magnetic fields from the actual antenna. The validated antenna model was then added into a simulated mine entry (tunnel) with three meshed surfaces (i.e., left and right ribs/walls, and the roof). The simulated magnetic field distributions around the antenna with and without the steel mesh were compared. The results show that the presence of steel mesh increases the magnetic fields and causes equal-field lines to be further away from the field source. As a result, the size of the warning/stop zones of a PDS can be increased when the system is used in a meshed entry and false alarms could be generated. In addition, it is found that the equal-field lines are distorted in the meshed entry, particularly in the areas close to the mesh, which could lead to an inconsistent PDS performance. To avoid this inconsistency, PDSs should be kept at a minimum distance away from the steel mesh when possible.