Proximity, motion, and vision sensors observe the presence of a target object or read a series of shapes. In response, they signal a control system to act. Photoelectric proximity sensors observe changes in transmitted light using an optical receiver. When the receiver senses the passage or movement of a target object, it sends an output to a control system. Capacitive proximity sensors direct an electrostatic signal to a target, sending an output to the PLC when they sense a change in capacitance. Inductive proximity sensors generate an electromagnetic field, transmitting an output to the PLC when a metallic object enters that field. Ultrasonic proximity sensors verify a target item's position by emitting high-frequency sounds and observing how quickly these soundwaves return. Vibration sensors read the vibration frequency of vital equipment and the axial direction of its motion to diagnose issues like imbalance or bearing failures. Vision sensors and code readers observe visual shapes like barcodes and perform actions like sorting boxes on a conveyor or calling up pricing and product data on a device.