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Mining Contract: Through-The-Earth Wireless Real-Time Two-Way Voice Communications

Contract DetailValue
Contract #200-2008-25720
Start Date8/1/2008
End Date8/31/2010
Research Concept

The goal of this project is to design, build, and demonstrate a battery-powered, through-the-earth wireless voice communication system for overburdens of up to 600 feet. Work to extend the range to 1,200 feet will also be specified. The design will be intrinsically safe for use in a methane environment. Besides voice communication, it will feature:

  • text messaging - Text messaging transmission requires less energy than voice. When battery power is low, switching from voice to text can conserve energy.
  • beacon transmission - A key will be provided which, when pressed, will transmit a tone. This will provide a beacon to help locate trapped miners.
  • instrument data output transmission - Terminals will be provided to transmit, in binary code, data from instruments such as oxygen, carbon monoxide, or methane gas monitors, or temperature monitors.

The technical approach will use magnetic coupling between transceivers underground and on the surface. The mining environment is electromagnetically very noisy both inside and outside the mine. Electromagnetic noise originates from both man-made machinery and natural atmospheric disturbances. To meet Mine Safety and Health Administration (http://www.msha.gov) regulations for intrinsically safe equipment, transmitter power is greatly restricted. Consequently, advanced filtering and noise cancellation will be employed to extract the signal from noise.

Program Area

Contract Status & Impact

This contract is completed. To receive a copy of the final report, send a request to OMSHR@cdc.gov.

A prototype, through-the-earth communication system was constructed and tested in the laboratory. The system worked as expected without the presence of external electrical noise. It was also tested at a stone mine through 200 feet of overburden. However, when simulated noise was introduced, reception by the surface transceiver was adversely affected. The design was revised to incorporate appropriate noise filtering and cancellation techniques to make the system usable for field tests.

The through-the-earth unit was then tested at the NIOSH Experimental Coal Mine in Pittsburgh on November 5, 2009. The system delivered two-way, real-time voice, through-the-earth communication when the transmitting antennas and receiving antennas were directly in-line vertically (approximately 100 feet), as well as when the surface transceiver was moved about 300 feet off the vertical axis. In a follow-up demonstration on April 16, 2010, real-time, two-way voice and text communications were successfully established between a point outside the portal of the Experimental Mine and a point inside the mine, approximately 1,000 feet away.

In-mine tests of the prototype communication system were conducted at a mine in southwestern PA on August 10, 2010. The cover was approximately 580 feet. Two-way communications were established via beacon, text, and real-time voice at relatively low power levels (antenna currents were approximately 1.5 amps). Electrical noise sources were nearby both underground and on the surface. The transceiver on the surface was in proximity to the elevator and power lines approximately 100 feet away. The underground transceiver was located near the trolley line. Voice reception on the surface was judged to be of excellent quality; underground voice reception was marginal and was attributed to a design deficiency in the underground receiver.

 
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