A ray of light

Nov 1, 2007 12:00 PM, By Mary Rose Roberts

Barrett said the system is self-healing, automated and has a patented middleware solution that controls latency through multiple wireless hops on the network to the degree that the system supports video in addition to voice and data. In addition, the network supports several Wi-Fi accessories, including a Wi-Fi telephone that can be linked to a PBX and offers push-to-talk, paging, eight hours of talk time and 160 hours of standby time.

As part of the system, coal miners are armed with Wi-Fi radio frequency identification, or RFID, tags that are mapped to specific individuals and can be set to broadcast in seconds. To pinpoint users within a range of about 10 feet, location data are transmitted to a graphical user interface map of the mine to track movements of assets and miners in real time at the command-and-control level. The company also is pilot-testing Ethernet-based video cameras.

Barrett said the system hasn't been tested in its entirety because the company awaits MSHA sign-off regarding the agency's intrinsically safe standard, but he expects to receive approval later this year. However, the solution will cost from $200,000 to more than $1 million, depending on the size of the mine.

The low-power ZigBee protocol also is being tested for use in coal mines, said Jack Sun, president and CEO of Helicomm, because it supports large mesh networks. The company offers MineTracer, a ZigBee-based wireless data and tracking system.

“Most of the folks who try to address the problem of RF underground try to increase power to blast the RF signal farther, and unfortunately that has limited success in mining environments,” Sun said. “So the approach that we've taken to utilize ZigBee is that we have very low-power radios, and then we use a lot of them to establish an infrastructure that allows multiple routing paths and multiple means of communications.”

The system includes data radios and a network controller that sits in the mine office or at company headquarters. From that point, a serial communications bus is run into the mine — a wired communications backbone such as Ethernet, fiber or a leaky feeder can be used. Once in the mine, a subnet controller, or network manager, taps into the backbone, assigns addresses and maintains network communications.

At that point, all communications in the mine are wireless and access points scattered throughout the mine — typically about 200 to 300 feet apart — support redundancy and ensure there is no single point of failure.

In addition, intrinsically safe mobile transponders affixed to coal miners' gear report location data to the access points. “One of the beauties of the system is the mobile transponders,” he said. “We actually can interface them to equipment, so if you have a methane sensor, we can interface to the transponders to extract that information so you can know what the conditions of the mine are through that system.”

Mine operators can expect to spend $35,000 to $50,000 per mile for the system, Sun said.

ONE CRITICAL POINT these technologies don't address is transmitting radio communications during a mine disaster, where rock and dust not only trap miners but also create a veritable RF tomb in which signals quickly fade and then disappear. J.C. Miller, CEO and president of VitalAlert Communications, believes his team of researchers has found the solution to communicating under these circumstances.

The company offers through-the-earth communications that are interoperable with existing land mobile radio technology to support communications with miners or emergency workers who have entered the subterranean environment in the aftermath of a disaster. The technology transmits near-real-time, two-way communications through concrete, dust or debris using a very-low-frequency (VLF) system.

“VLF is a proven technology that's been used by the military for years and is a signal that actually allows a transmission to go through the earth,” Miller said.

He said the proprietary technology puts an RF signal in a virtual “envelope,” broadcasts it through the earth and then opens the envelope once it reaches the area where the signal needs to be propagated.

At the heart of the system are portable boxes, each supported by an amplifier and an antenna, that are placed both above and below ground. To build out a scalable system, several boxes would be required, similar to a cell system. Each box has a range that is defined by the geology, the amount of power needed and the size of the antenna used, Miller said.

During an emergency, coal miners could keep a box in the underground storage facilities where safety equipment is located.

“It would be a standalone unit where, if a rescue team is coming in, they can have an idea where the miners were and set up their equipment,” Miller said. “Depending on the mine geology, the depth of the mine and a number of issues relating to whether the communication comes from surface to underground or from horizontally, it would give them a range of coverage that they would be able to communicate two-way voice through the earth.”

But it hasn't been an easy road for the technology, Miller said. Currently, the system only operates at depths of about 650 feet — short of the average mine depth of 1000 feet. In addition, few in the industry are willing to test the technology, because many engineers are still stuck in the world of existing terrestrial systems.

“Mine companies tend to band-aid existing systems and try to use what's off the shelf. I really think that part of it is that they want it now,” Miller said. “The case here is that we have to embrace this, advance this and have a five- to 10-year vision. But when I talk to people, they say they want the technology to look like a cell phone. Well, that's not what it is. Maybe it will be there someday, but it's not where it is now.”

It's a reality that hits Hammonds hard. While he fondly remembers the camaraderie during his days mining coal, the tragedies in West Virginia and Utah bring sorrow to his heart. He empathized with all the families at the mine disasters who hoped for hours that loved ones would be found and, at the same time, anguished over questions of why communication systems were not in place to track personnel. And he watched on television as the overall lack of communications, stemming in part from a singular dependence on two-way radios, hampered rescue operations.

“Mines are still using the same technology they've used for years — there's no Internet access or wireless access inside the mine, just the leaky feeder and two-way radios,” Hammonds said. “Two-way radios have to be line-of-sight to work underground. They just don't work. There's just not an existing capability to do 100% wireless communications underground.”

PROXIM ACCESS POINTS TWEAKED FOR MINE COMMUNICATIONS

Proxim Wireless Corp. collaborated with Hannah Engineering on a wireless communications system that was approved in June 2007 by the state of West Virginia's Office of Miners' Health Safety and Training (MHST) for use in underground mines.

Hannah's Wireless Integrated Technology Systems, or WITS, solution is a fault-tolerant, self-healing communications and tracking system used within mines to send and receive voice, video, data and location information. It now incorporates Proxim's ORiNOCO AP-4000M wireless-mesh access points.

Robert Fitzgerald, CEO of Proxim, said the company identified the mining industry as a strategic vertical market, but originally focused only on open-pit — such as diamond — mines that do not need to meet intrinsically safe requirements.

That focus changed when Hannah approached the company and asked permission to modify its access points to meet the requirements of MHST and then meld them into the WITS system, Fitzgerald said.

WITS uses several of Proxim's mesh access points within a mine to send and receive information from the miners, foremen and maintenance crews. It is designed so if one access point is damaged, the signal can be rerouted to another access point, according to the company. The capability is enabled by Proxim's self-healing mesh technology that automatically reroutes traffic in the event a node in the network goes down, Fitzgerald said.

Hannah has submitted WITS to the Federal Mine Safety and Health Administration (MSHA) for intrinsic safety certification and anticipates that the system will be certified to be intrinsically safe by MSHA this month.
— Mary Rose Roberts