Photometric detector and measuring system

Claim 1

In a photometric system for determining the height of an object above a surface, light source means for directing a single and continuous beam of light in a path generally parallel to the surface, light detecting means disposed in the path of the beam, said beam having a first portion passing directly and continuously to the light detecting means and a second portion which is at least partially obstructed by the upper portion of the object, said light detecting means including first photosensor means for receiving light from the first portion of the beam and providing a reference electrical signal corresponding to the intensity of said first portion and second photosensor means for receiving light from the second portion of the beam and providing a height electrical signal corresponding to the intensity of said second portion, means for comparing the reference and height signals and providing a control signal when the height signal is at a predetermined level relative to the reference signal, bistable logic means connected for receiving the control signal assuming predetermined output state in response thereto and logic gate means receiving inputs from The bistable logic means and from an external timing signal source, said gate means providing an output signal if the cistable logic means is in its predetermined state when a timing signal is received.