Optical detector system for strip velocity - responds to sequence of triangular patterns resulting in two similar sawtooth wave form inputs to electronic circuit

摘要

The surface speed measuring equipment has a detector unit (8, 9) adjacent to a moving strip (3) and separated from it by a plate (2) with two parallel slits (10, 11). The detectors are typically photodiodes and are connected in an electronic circuit containing amplitude threshold level discriminators (13, 14), bistable units and a logic circuit with AND and OR gates. The moving strip carries a special pattern, typically in the form of a linear sequence of triangular shapes, so that the optical pick-up through the slits generates a pair of saw-tooth wave forms of similar shape but out of phase. The circuit develops a sequence of square pulse d.c. signals with the polarity dependent on the direction of movement of the strip.