Method and apparatus for combustible gas detection in dirt laden atmosphere

Claim 1

An apparatus for use in the detection of combustible gases in a primary zone in which combustiblE gases may be present and for use with a subatmospheric pressure source and a source of fluid under pressure greater than atmospheric, said apparatus comprising: a detection head to be positioned in said primary zone and including a base, detector means mounted on said base, means mounted on said base and defining a diffusion type barrier about said detector means, said base and said barrier means being a unit of a given size, and an enclosure wall defining a space about said barrier and at least in part being formed by a filter, said enclosure wall being so formed that there is a distance between said unit and said filter, said enclosure wall having a conduit connection communicating with the space within said wall, said enclosure wall comprising a main body of generally cup-shaped configuration having a closed end and an open end, said body being threaded at said open end, and cap means threaded onto said open end and closing said open end, part of said cap means being formed by said filter, the base of said unit being removably attached to said closed end, said conduit connection being in said body and communicating with the interior thereof at a location that is farther removed from said filter than is the position of the barrier with respect to the filter; and control means communicating with said sources and with said conduit connection for applying a subatmospheric pressure to said space to create an air flow from said area through said filter into said enclosure and about the barrier, periodically removing the applied subatmospheric pressure and briefly replacing it with a fluid pressure above atmosphere in said space to create a counterflow in said conduit and head sufficient to dislodge contaminates that may have lodged in said filter, and thereafter again applying said subatmospheric pressure to said space.