Among various types of switches, there is a component that has "feel" ability to approach its object - a displacement sensor. This is the proximity switch, which uses the proximity sensor's sensitivity to the proximity of the object to achieve the purpose of turning the switch on and off.
When there is an object moving towards the proximity switch and approaching a certain distance, the displacement sensor only has “perceived” and the switch will act. This distance is usually called the "checkout distance." However, different proximity switches detect different distances.
Sometimes the object to be inspected is moved one by one to the proximity switch and one by one at regular intervals, so that it repeats continuously. Different proximity switches have different response capabilities to detection objects. This response characteristic is called "response frequency".