Pneumatic shift register sequence control - has threshold gate to ensure interlock signal line pressure is below given pressure

摘要

An interlocked sequence control of processes using pneumatic valves is based upon a shift register technique using stages that ensures correctness of operation by requiring a specific signal pressure before the sequence may advance. Each side of a pneumatic cylinder is controlled by a signal (7) from a shift register stage (40), consisting of a bistable function (41), threshold gating (36) and interstage gating. When the signal from an actuator limit switch (16) is too high the threshold gate output (30) is low and the bistable is not set to generate an output (7). When the time has evacuated the pressure falls and the bistable changes state. The interstage gate (13) allows successives stages to be set to advance the sequence.