Proximity sensor with zero adjustment

Claim 2

In a proximity sensor, the combination comprising an emitter assembly having a cylindrical passageway, a fixed orifice disposed in said passageway dividing the passageway into an output chamber and a b ack pressure chamber, a sensing nozzle connected to said back pressure chamber for wasting pressure fluid from the back pressure chamber in inverse proportion to the proximity of an object to the sensing nozzle, an orifice tube located within said output chamber axially aligned with said fixed orifice adapted to be connected to a source of pressure fluid and discharge a jet of pressure fluid through said fixed orifice into said back pressure chamber, and means for axially positioning said orifice tube to thereby vary the pressure in said output chamber for a given pressure in said back pressure chamber.

Claim 3

A proximity sensor as set forth in claim 1 wherein said orifice tube is provided with a closed end remote from said fixed orifice and having an outside diameter less than the diameter of said output chamber, axially spaced apart O-rings carried by said orifice tube bearing against the cylindrical wall of said output chamber to thereby provide a cylindrical annular chamber pressure sealed from said output chamber, an inlet port in said orifice tube between said O-rings for discharging pressure fluid from said annular chamber into said orifice tube, and a supply port in the wall of said output chamber for introducing pressure fluid into said annular chamber, and wherein said means for axially positioning said orifice tube comprises a collar formed on said orifice tube provided with external threads engaging internal threads on the wall of said output chamber whereby rotation of said collar in forward and reverse directions axially positions said orifice tube toward and away from said fixed orifice.