The RPBR is a highly versatile self-contained modularized photoelectric MAXI-BEAM Sensor head contains the complete modulated photoelectric amplifier as well as the emitter and receiver optoelements. The basic MAXI-BEAM is an ON/OFF switch consisting of three modules, a sensor head, a power block and a wiring base. An unique, patented, "programming ring" (supplied with each sensor head) enables you to program your choice of "light" or "dark" operate mode, sensing range and response time. MAXI-BEAM sensor heads have an easily-accessible multi-turn SENSITIVITY control for precise adjustment of system gain. Interchangeable sensor heads are rotatable in 90- degree increments and are available in opposed, retroreflective, diffuse, convergent and fibre optic models. Each sensor head also includes Banner's exclusive, patented Alignment Indicating Device. Sensitivity adjustment is easily accessible, located on top of sensor head beneath O-ring gasketed cover