Communications: electrical – Selective – Having electron beam device
Patent
1974-09-11
1976-01-20
Wilbur, Maynard R.
Communications: electrical
Selective
Having electron beam device
299 12, 73 676, 73 69, 61 35, 61 85, H04B 1100, E21C 3700, E21C 4100, E21C 4500
Patent
active
039342190
ABSTRACT:
The effectivenss of a seal for extinguishing fires in an underground mine passage is determined by transmitting acoustic energy from a first site toward the seal. The acoustic energy is detected at a second site on the opposite side of the seal from the transmitting site. To provide for remote monitoring of the seal, acoustic transmitter and receiver means are lowered into the passage to the first and second sites through vertical bores. The effectiveness of the seal is determined by the amplitude of the detected acoustic energy. The size of any hole in the seal is determined by comparing the amplitude of the detected energy after the seal has been started and prior to the sealing operation commencing. The acoustic energy has a carrier frequency that randomly varies over a relatively broad band to prevent acoustic nodes in the passageway. The carrier frequency is varied between approximately 500 KHz and 4,000 KHz to enable the energy to be somewhat directional in the passage and to have a relatively uniform field in the passage downstream of the seal. To provide a relatively high signal-to-noise ratio and effectively preclude detection of energy arriving at a receiver by way of flanking paths, the acoustic energy is pulsed and the receiver is gated on only during a time interval when it is expected that the pulse will be received at the second site via the passage.
REFERENCES:
patent: 3211252 (1965-10-01), Smith, Jr. et al.
patent: 3264864 (1966-08-01), Reid et al.
patent: 3583165 (1971-06-01), West et al.
patent: 3630307 (1971-12-01), Kamps et al.
Blum T. M.
Fraser Donald R.
Sadowsky Gersten
The United States of America as represented by the Secretary of
Wilbur Maynard R.
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