Device for precise detection of very slow rotation of rotor

摘要

The device measuring rotation of a circular disc (14) or roller, which carries a peripheral cam (16), is based on two mechanical or reed switches (24,26) at an angular separation ( alpha ) not less than the angle ( alpha min) subtended by the cam at the centre (22) of the circle. The switches are wired to an electronic counter which is started by closure of one switch (24) by the cam, and read when the other switch (26) is closed in its turn.