The proximity sensor is a general term for sensors that detect objects without touching them instead of contact detection methods such as limit switches. The sensor converts the movement and presence information of the detected object into an electrical signal. Among the detection methods that convert the information into electrical signals, some methods utilize the eddy current generated in the metal body of the detection object due to electromagnetic induction, methods that change the capacity of the electrical signal due to the proximity of the detection object, and methods that use a sharp stone or a guide switch, etc. ATO.com will introduce the basics such as the principle of operation, types, and applications of the proximity sensors in detail in this article.