proximity switch
Proximity switches , also proximity sensor , proximity switch , or ( arrival ) proximity sensor called, are sensors that on approach d. H. react contact-free without direct contact. Proximity switches are used, for example, in technical processes to detect the position of workpieces and tools, and to trigger safety measures.
Types of proximity switches
- Inductive proximity switches : They react with ferromagnetic as well as non-magnetic metallic objects and with graphite.
- Capacitive proximity switches : They react to both metallic and non-metallic materials. When an object approaches, the oscillation frequency of the proximity switch oscillating circuit changes.
- Magnetic proximity switches (e.g. reed switches or reed contacts , see reed relays , or Hall sensors ): They react to a magnetic field .
- Optical proximity switches : They react to light reflection .
- Light barriers : They evaluate the interruption of a light beam.
- Ultrasonic proximity switches: They evaluate the reflection of an ultrasonic signal on an obstacle.
Examples
- Light barriers and in modern elevators: light grids monitor the doors of elevators . As long as the light beam is interrupted, the door cannot close.
- A magnetic proximity switch on a hydraulic or pneumatic cylinder detects when the piston has reached the front or rear end position. It triggers a signal with which the corresponding directional control valve interrupts or releases the supply of the working medium (hydraulic fluid, compressed air ).
- In smartphones, optical proximity sensors detect a rapid approach of the head or ear when answering a call, so that the touchscreen can be switched off.
literature
- F. Ebel, S. Nestel: Textbook proximity switches . Festo Didactic GmbH & Co. KG, Esslingen 2003, ISBN 3-8127-3045-6
- Berthold Heinrich, Petra Linke, Michael Glöckler: Basics of automation - sensors, regulation, control . Springer Fachmedien, Wiesbaden, 2015, ISBN 978-3-658-05960-6 .
Web links
Individual evidence
- ↑ Greg Milette, Adam Stroud: Professional Android Sensor Programming . John Wiley & Sons, May 17, 2012, ISBN 978-1-118-22745-9 , p. 85.