Emitter-Receiver Type Photo-Electric Control The Commercial Protector System® provides protection on doors up to 30 feet wide. Contains emitter, receiver, mounting brackets, and operator interface. 24VAC, use CPS-L if Solid State Logic 3 or Medium-Duty Logic Control Board unit. OPEN only (all LiftMaster operators) after vehicle passes through infrared beam. Signal beam is projected across vehicle path and, when broken, sends a signal to open the door.