Automatic damper control

Claim 1

An automatic damper control comprising: (a) a damper for use in a flue or the like; (b) diaphragm means adapted to expand and contract in response to pressure variations in said flue; (c) sensor means for sensing the pressure in said flue, said sensor means being connected to said diaphragm means, said sensor means comprising means for generating a plurality of beams of light, photoreceptors, and collimating means adapted to collimate each of said beams of light onto a photoreceptor; (d) blocking means for blocking at least one of said beams of light, said blocking means being operatively associated with said diagphragm means and being adapted to be displaced relative to said beams of light in response to movement by said diaphragm means; (e) drive means for moving said damper means in response to pressure variations in the flue; (f) wherein said collimating means comprises a collimating plate arranged between said light generating means and said photoreceptors, said collimating plate comprising an orifice aligned with each of said light generating means and said photoreceptors so as to collimate each of said beams of light onto each of said photoreceptors; (g) wherein said blocking means comprises blocking plate means arranged between said means for generating said beams of light and said photoreceptors adjacent said collimating plate; (h) said blocking plate means being arranged relative to said orifices such that a single one of said orifices may be exposed in response to movement of said blocking plate means; and (i) wherein said diaphragm means comprises a bellows, said blocking plate means being mounted on said bellows such that said blocking plate means move relative to each of said orifices as said bellows expands and contracts in response to pressure variations in the flue.