It is called an rpm (revolution per minute) to the unit that is used to express the angular velocity. It is the number of complete turns a body gives around an axis.

Proximity or range sensors are used in many installations requiring an action according to the distance (D) of an object.
They are also used in robotics to control the movement according to the environment, in motorized or domotic installations, the applications can be many and very different.
There are a variety of proximity sensors, including the most common are position switches, Capacitive sensors, inductive sensors, photoelectric sensors where an emitter (E) and a receiver (R), ultrasonic sensors and magnetic sensors are required.
Each of these sensors have the same function, but each of them uses different systems for the detection, either by contact, sound, etc.
Its detection capacity varies according to the type of sensor, and can vary from millimeters to meters. We can vEr these sensors in automatic floor cleaning systems, safety barriers, rear parking sensors for cars, mobile phones, etc.