Combustible vapor detector

Claim 1

Apparatus for detecting combustible vapors comprising: heat sink means, the structure of the heat sink means defining a reference chamber and a sensing chamber; the sensing chamber being characterized by a lower section which has a bottom portion and sidewalls which have a preselected interior perimeter; the reference chamber being essentially sealed; at least one entrance passage and one exit passage being physically separated one from the other and both being located in the bottom portion of the lower section of the sensing chamber; first and second essentially identical filament means, both of the filament means being adapted to vary in resistive value as a function of the amount of combustible vapor present in air which comes into contact with the filament means; first circuit means coupled to the first and second filament means, the first circuit means being adapted to generate a first alarm signal if either filament means breaks or burns out; the first and second filament means being located essentially within the sensing chamber and reference chamber, respectively; second circuit means comprising a wheatstone bridge circuit having first and second resistive circuit legs, the first leg comprising the first and second filament means, the resistive value of the first and second legs being selected such that when there are substantially no combustible vapors in the sensing and reference chambers the wheatstone bridge is unbalanced, however, if there is a significant amount of combustible vapor in the sensing chamber and substantially none in the reference chamber, the wheatstone bridge goes through balance to an unbalanced condition in the reverse direction; alarm circuit means being coupled to the wheatstone bridge, the alarm circuit means being adapted to generate a second alarm signal if and only if the wheatstone bridge goes through balance to an unbalanced condition in the reverse direction; first conduit means in open communication with the entrance passage of the bottom portion of the lower section of the sensing chamber; second conduit means in open communication with the exit passage of the bottom portion of the lower section of the sensing chamber; air pumping means in communication with the second conduit means, the air pumping means being adapted to continuously draw air, which may or may not contain combustible gases or vapors, into the first conduit means, through the sensing chamber, and out of the second conduit means; air sampling and calming means and flame arresting means, both the air sampling and calming means and the flame arresting means being located in the lower section of the sensing chamber; the flame arresting means being physically located below the air sampling and calming means and being located so as to overlap the entrance and exit passages in the sensing chamber; the air sampling and calming means being an essentially solid non-porous member, the outer perimeter of the member being slightly smaller than the interior perimeter of the sidewalls of the lower section of the sensing chamber such that a relatively small space exists between the sidewalls of the lower section of the sensing chamber and the air sampling and calming means; and the air sampling and calming means having a much higher resistance to the flow of air therepast than the flame arresting means such that only a relatively small amount of the total air continuously drawn into the sensing chamber by the air pumping means continuously passes above the air sampling and calming means and enters the portion of the sensing chamber which contains the sensing filament.