In all types of switches, there is a displacement sensor that has a "perceptual" ability to approach its object. Using the displacement sensor to the sensitive property of the close to the object to control the switch pass or break, this is the proximity switch.
When an object moves toward the proximity switch and is close to a certain distance, the displacement sensor is "perceived" and the switch moves. This distance is usually called "checkout distance". But different proximity switches have different detection distances.
Sometimes detected objects are at a certain time interval, one after another to move to the proximity switch, another one to leave, so repeat. The different proximity switches have different response ability to the detection object. This response feature is called the response frequency.