May 29, 2011
Underground Tracking: Zonal vs. Networked Probabilistic Location Systems

The mining industry clearly understands the need and importance of tracking personnel operating underground in real-time, not just to comply with regulatory requirements, but to understand all activity in a mine as it occurs.  Underground personnel and asset tracking products continue to become available to the mining industry, and as expected, these products typically utilize one of a number of technical approaches to determine a person’s or asset’s position.

One common tracking method, generally referred to as zonal, typically uses RF identification (RFID) tags and requires the installation of a hardwired infrastructure throughout the mine, or at least in the areas tracking is required.   The infrastructure typically consists of RF access points placed in strategic points along travel ways and other commonly used entries.  Hardwired interfaces provide electrical power to the access points and wire or fiber links provide the communications between this equipment.  Personnel are responsible for carrying tracking ID tags – these tags briefly communicate with a fixed access point when the miner is in the close vicinity of one of these devices.  

Strata CommTrac takes a more state-of-the-art networking probabilistic approach to providing real-time personal and asset position reporting.  The networked approach also uses a series of nodes placed throughout the mine, however, no backbone infrastructure of any kind is required – each node uses inexpensive replaceable batteries rather than a hardwired power source.  Personnel are issued rechargeable tracking (and text capable) units that routinely survey their environment.  These tracking and communication devices can take advantage of multiple nodes to calculate their location inside the mine.  Because the nodes do not need to constantly expend energy transmitting and querying any RFIDs that may or may not be in the area, they draw very little power – permitting them to last up to a year on their battery supply.  As the mining operating proceeds, the nodes are simply unclipped from roof supports and moved or added as needed.

Zonal (RFID) methods rely on personnel passing though specific points, or virtual gates, throughout the mine.  In theory, this allows an operator to know where a miner was at some point in time based on the last zone he passed through.  All RF-based communications, however, are non-deterministic.  Interference effects and blockage mean that not all point-to-point messages get though.  In the previous scenario, then, the operator may be misled to believe personnel are currently in one zone when in fact they are now located in an adjacent zone.  This can become dangerous misinformation in a post-event situation.

As previously noted for the networked approach, each tracking device communicates with multiple nodes.  These nodes have overlapping coverage areas, and any disruptions in communication are mitigated by the redundant architecture.  Tracking (and communication) is continuous and not dependent on a message sent at a specific point along the entry.  Furthermore, the use of multiple sources allows personnel to be located at a point between nodes, not just near certain points.

Although zonal systems are effective at maintaining a historic account of personnel and asset movements through specific points in a mine, networked approaches offer a clearer picture of real-time mine operations.  This becomes especially important in a post-event scenario.  Additionally, the use of a fully wireless networked product allows the network to easily expand along with the mine.  Network expansion literally takes minutes rather than days.  This eliminates periods of time in which coverage at critical areas (e.g. the mine face) is not available – enabling regulatory adherence and, most importantly, improving miner safety.

For more information, please contact Chris Adkins at 304-546-5946 or