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

The illuminated optical proximity switch of a smartphone (BlackBerry Leap)

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The flashing of the proximity switch on a smartphone during a call

• 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

Proximity sensor of an iPhone 3GS

• 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

• Training documents for various proximity switches; ifm electronic GmbH

Individual evidence

1. ↑ Greg Milette, Adam Stroud: Professional Android Sensor Programming . John Wiley & Sons, May 17, 2012, ISBN 978-1-118-22745-9 , p. 85.