Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1978-01-05
1984-04-17
Caldwell, Sr., John W.
Communications: electrical
Condition responsive indicating system
Specific condition
73 23, 422 98, G08B 1710
Patent
active
044437919
ABSTRACT:
Alarm-indicating gas detection apparatus including a first semiconductor gas-sensing element having one electrical property which varies significantly with increasing concentrations of a first undesirable gas and less significantly with increasing concentrations of a second undesirable gas and a second semiconductor gas-sensing element having the same electrical property which varies significantly with increasing concentrations of the second gas and less significantly with increasing concentrations of the first gas. The electrical property of both gas-sensing elements tends to vary similarly with age and with changing conditions such as temperature and relative humidity. A compensation system is used to cancel out errors due to variations in the electrical property. Threshold circuits are used to distinguish between first and second undesirable gases and to generate alarm signals. A gas combination detection circuit generates an alarm whenever a significant concentration of both first and second gases are present or whenever a third detectable undesirable gas, such as CO, is present. A logic gating network is used to generate various alarm initiating signals. Signal-generating elements responsive to these alarm-initiating signals generate a different alarm indication for each different alarm state detected. The system may include an oxygen depletion detection system with the placement of the oxygen depletion sensor close to at least one of the first and second gas-sensing elements for usage at temperatures significantly lower than the lower operating limit normally permitted by the gas-sensing elements.
REFERENCES:
patent: 3801972 (1974-04-01), Ho Kim et al.
patent: 3864628 (1975-02-01), Klass et al.
patent: 3961248 (1976-06-01), Kawamura
patent: 4012692 (1977-03-01), Eicker
Risgin, administratrix by Geraldine J.
Risgin, deceased Ojars
Caldwell Sr. John W.
Deimen James M.
Myer Daniel
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