Communications: electrical – Condition responsive indicating system – With particular system function
Patent
1977-02-18
1978-10-10
Kreitman, Stephen A.
Communications: electrical
Condition responsive indicating system
With particular system function
73 24, 340539, 340632, G08B 2100, G01N 2902
Patent
active
041199502
ABSTRACT:
Apparatus for monitoring gas content on a site, to provide an indication if an undesirable gas content occurs, comprises a transmitter for feeding ultrasonic waves through the gas to a receiver. The ultrasonic waves are frequency-modulated and the phase of the modulation at the receiver relative to that at the transmitter is monitored. Either the relative phase is maintained constant, for example by a phase-locked loop so that the modulation frequency varies as a function of the gas content, or the frequency is maintained constant and the phase varies with the gas content. Any appreciable change in the frequency or phase may indicate a potentially undesirable change in the gas content. A plurality of transmitter/receiver pairs can be enabled in sequence to monitor a large area, the respective frequencies or phase displacements being monitored by a central processor.
REFERENCES:
patent: 3047815 (1962-07-01), Boose
patent: 3120750 (1964-02-01), Root
patent: 3199037 (1965-08-01), Graves
patent: 3427481 (1969-02-01), Lenahan et al.
patent: 3449748 (1969-06-01), Thyssens
patent: 3613092 (1971-10-01), Schumann et al.
patent: 3624626 (1971-11-01), MacCreadie
patent: 3789655 (1974-02-01), Passeri
patent: 3828607 (1974-08-01), Janzen et al.
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