GB1506651A - Particle flow sensors - Google Patents

Abstract

1506651 Detecting particles photo-electrically DICKEY-JOHN CORP 4 Oct 1975 40716/75 Heading G 1A A particle sensor comprises two housing members defining a passageway which is lined with transparent wall portions positioned so that they will be wiped by particles as they fall through; and a light source and light responsive means for providing a pulse signal when a particle passes, the transparent wall portions overlying the source and responsive means. Seed released from a planting machine hopper, Fig. 1 (not shown) fall through a sensor, Fig. 3, comprising complementary housing portions 50, 51 defining a passageway, of which opposing wall portions are coated with a clear expoxy resin 62, 63 Fig. 4 which resists the accumulation of electric charge that might attract dust. Elimination of dust is further assisted by the shaping of the resin portions 62, 63 to facilitate the wiping of them by the passage of seeds. A LED 23a mounted on a circuit board 70 illuminates a window area of the coating 62; and phototransistors 27a (and 28a not visible) mounted on a board 84 behind a window area of the coating 63 emit a pulse every time a seed passes the window area. The phototransistors 27, 28, Fig. 2, whose current decreases when a seed is sensed, supply a negative pulse to a capacitor 41, the pulse being inverted by a transistor 40 and shaped by a small capacitor 46 to produce an output current pulse of the collector of a transistor 44. The normally-illuminated quiescent current of the phototransistors 27, 28 is amplified at 36, any superimposed pulses being smoothed out by a capacitor 32, and used to regulate the supply to the LED 23, to stabilize the illumination in the passageway against residual dust on the windows. The major portion 22 of the circuit is mounted on the board 84, to protect it from the heat generated by the current limiting resistor 24, which is mounted on the board 70 in series with the LED 23. In another embodiment, Figs. 6, 7 and 8 (not shown), the epoxy window portions are constituted by a tubular insert (113) retained in recesses in the housing portions (102, 103).