photoelectric sensors, ultrasonic sensors, pressure sensors, distance measuring sensors, proximity sensors, rotary encoders, optical character readers, image sensors, optical inspection apparatus, exclusively for industrial use in assembly line production, input/output connectors for PLC (programmable logic controller), cables, optical fiber cable, optical modulators, optical isolators, optical switches and optical circulators, sensor and [ wire-sharing ] * wire-saving * link system, namely sensors, sensor input/output units, sensor control units, and boosters, all linked by cables and connectors, detachable handy monitors to be connected to the controllers and to display conditions of controllers, boosters to be used in signal transmission circuits, connectors for signal cables, area sensors to detect objects by utilizing parallel light beams which pass on a plane, sensors which optically detect and display operator's picking of assembly parts from storage shelves, sensors to detect man's hands entering to press machines, sensors to detect lack of resin coating, sensors to detect minute protrusions of electric wire surfaces, ultrasonic sensors to detect liquid level, detectors of overlapping of metal plates, color discrimination sensors, sensors to measure sizes of objects by making the objects traverse parallel light beams which pass on a plane; all the aforesaid excluding computer hardware and computer software