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PROGRAMMABLE_CONTROLLER_PHOTOELECTRIC_INTERFACE

2015-03-20 02:00  
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PROGRAMMABLE_CONTROLLER_PHOTOELECTRIC_INTERFACE
This circuit is an IR sensor with a timed positive output pulse that will operate with older and slower PLCs. Some of the early PLCs have scan times of 15 ms or more. The sensor's extended output pulse can be set, by R3, to a time period longer than the controller's scan time, The sensor can also be used as a stand-alone circuit to operate a counter, a valve, an indicator, or any other electrically controlled device. As long as nothing is blocking the IR light source, the emitter of phototransistor Q1 is high and 555 timer IC1 is set in the READY state. When an object blocks the light source, Q1 turns off, sending a negative pulse to the trigger input at pin 2 of IC1, producing a timed output pulse. R3, and C2, determine the length of the output pulse. Larger values produce longer output pulses.