through-the earth mine communication systems
TRANSCRIPT
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Through-the Earth Mine Communication Systems
Michael R. YenchekSr. Electrical EngineerPittsburgh Research Laboratory
The findings and conclusions in this presentation have not been formally disseminated by the National Institute for Occupational Safety and Health and should not be construed to
represent any agency determination or policy. Mention of company names or products does not imply endorsement by NIOSH.
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Through-the-Earth Communications
Locator
Trapped Miner
Communicator
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Through-the-Earth Communications
• Frequencies less than 10,000 Hz• Long wavelengths in the thousands
of feet• Transmission Path
– Through overburden– Through coal pillars
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Transmission Mode• Real-time voice• Voice message• Text message• Beacon
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Transmission Rates
• 2.5 kbps – Real-time digitized voice
• 500 bps – Voice mail with data & text
• 100 bps – Digital data & text
• 10 bps – Text @ 1 keystroke per second
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Through-the-Earth Transmissionis affected by:
• Frequency• Transmitter power• Nature of overburden
– Earth conductivity– Depth of cover– Strata anomalies
• Electrical Noise• Antenna
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TTE Transmission: Frequency
• Lower frequencies transmit easily through solid material
• At low frequencies there is a trade-off with transmission rate and range
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TTE Transmission: Transmitter Power
• Limited by safety considerations• Permissibility
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TTE Transmission: Nature of Overburden
Material Conductivity, S/m-------------------------------------------------------------Dry Limestone 0.001Sandstone 0.01Salt 0.15Coal 0.25Salt water 5
Higher Conductivity = Less Range
Sig
nal R
ange
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• Typical overburdens range from 300 ft. to 2000 ft .
• Strata Anomalies– Aquifers– Mined-out seams
TTE Transmission: Nature of Overburden
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• Underground– 60 Hz and harmonics
(motors, transformers, etc.)– Decreases during emergency
• Surface– Lightning– High-voltage power lines– Generators
TTE Transmission: Electrical Noise
Signal level must exceed noise level
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Surface Noise Reduction
• Conventional Analog Filtering: 20 dB reduction
• Advanced Digital Filtering: 40 dB reduction
Performance goal of 40 to 50 dB for the deepest mines (2000 ft/)
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Rock Type Real-Time Voice Voicemail Data and Text
Dry-Limestone 2000 feet 2000 feet 2000 feet at 2.5 kbps
Sandstone 1200 feet 1500 feet 2000 feet at 100 bps
Depth vs. Rock Type and Data Rates
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TTE Transmission: Antenna
• Large loop of wire (air core)– Encompasses large surface area– Around coal block
• Multiple winding ferrite core – Compact – Portable
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Antenna Orientation
Good Coupling Poor Coupling
Transmitter
Surface Receiver
Loop
of w
ire
Loop of wire
Loop of wire
Loop of wire
Underground Transmitter
Underground Transmitter
Surface Receiver
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Underground Transceiver
• Through-the-earth and through-the-mine• Low power to ensure permissibility• Portable or fixed location• Voice, text, or beacon
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Surface Transceiver
• Can have larger antenna– Could encompass most of mine– Limited by terrain– Located above stationary transceivers
underground• Can have greater power
– Higher frequencies•Higher data rates
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Surface Transmission Through-the-Earth
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Transmission Through-the-Mine
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Deployment during Escape
• Communicate with underground and surface
• Multiple units available• Loop around coal pillar• Beacon mode
(This information will be depicted in a drawing)
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Deployment in Rescue Chamber• Communicate with surface
and/or rescue teams• Conserve battery life
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MaintenanceRoutine Periodic Function Tests
• Verify Through-the-Earth and Through-the-Mine communications periodically
• Confirm communication with surface each time chamber is moved
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A Magnetic Communication Systemfor Use in Mine Environments
• Competitive BAA award• Lockheed Martin Corporation, Syracuse, NY
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Objective: To develop and demonstrate a two-way
through-the-earth communication system for mines
• Laboratory prototypes
• Field demonstrations