http://nexflowair.com/plcflow_how_they_work.php The PLCFC combines a photo electric sensor to turn on the air when the target passes the sensor and to turn off the air when it leaves the sensor. (The unit is set to have a 2 second delay after it leaves the sensor but turns on instantaneously when it sees the target). In one example using an air knife, compressed air enters at point (A) into the air knife (B) only when the sensor (C) sees the target. The PLCFC is located at point (D). The target part (E) passes the sensor activating a solenoid to turn on the air flow to the air knife. The target travels on the conveyor (F). Two seconds after the target has passed the sensor, the air supply is turned off conserving energy. Different sensors are available for different applications and the units can be programmed for special applications.