Portable length probe with improved wheel pick-up arrangement

A portable length probe comprising

• a portable probe having a nose body with a wheel slot formed therein,
• a light passage bore formed in and extending through said nose body transverse to said wheel slot,
• a light-emitting element having a case therearound and effectively open at one longitudinal end for light emission therefrom,
• a photo-responsive element having a case therearound and effectively open at one longitudinal end only for light input therethrough to said photo-responsive element,
• said photo-responsive element case being effectively opaque to light of the frequency spectrum to which the light response element is sensitive,
• a wheel rotatably mounted in said slot for rotation therewithin by linear moving contact of a circumferential surface thereof with a surface to be measured,
• said light-emitting element case and said photo-responsive element case fitting in generally complementary relationship within said bore on respectively opposite sides of said wheel slot and having their open ends facing one another,
• said wheel having a plurality of transverse holes therein spaced apart at equal distances and on substantially equal radius centers,
• said transverse holes being each of substantially the same angular width around the annular extent of said wheel and being annularly angularly spaced apart a distance substantially equal to said angular width of one of said transverse holes,
• said holes being alignable with said bore having said cases and corresponding photo-responsive and light-emitting elements therein as a function of rotation of said wheel,
• and leads to said light-emitting and said photo-responsive elements for connection thereof respectively with a source of EMF and pulse counting means,
• a square wave generator connected in responsive square wave generating relation to the output of said photo-responsive element and forming two mirror-image square waves,
• two mirror-image differentiators and a full wave rectifier having two inputs, each of said mirror-image differentiators being connected between a respective mirror-image square wave output of said square wave generator and a respective input to said full wave rectifier,
• said full wave rectifier thereby yielding an output signal having two substantially identical differentiated pulses for each wheel hole pulse from said photo-responsive element, thereby enabling greater accuracy through count registries for the opposite sides of each hole.