Proximity sensor

Called proximity switches, and proximity sensor or proximity switch, using sensors that react to a non-contact approach, i.e., without direct contact. Proximity switches are used in industrial processes for recognizing the position of workpieces and tools, and as a trigger of security measures. For some proximity switches, the sensors and switches are combined in a single component.

Types of proximity switches

• Inductive proximity switch: you are both ferromagnetic as well as non-magnetic metal objects but on the occurrence of an eddy current.
• Capacitive proximity switches: They also react to non-conductive materials.
• Magnetic proximity switches (eg, reed switch or reed, see reed relays, or Hall sensors): they react to a magnetic field.
• Optical proximity switch: they react to light reflection.
• Photocell: photoelectric evaluate the interruption of a light beam.
• Ultrasound: proximity switches evaluate the reflection of an ultrasonic signal from an obstacle.
• Electromagnetic proximity switch, in which approach changes the resonant frequency of resonant circuits. They respond to both conductive and non-conductive materials on.

Examples

• Photoelectric sensors monitor the doors of elevators. As long as the light beam is interrupted, the door can not close.
• Of a hydraulic or pneumatic cylinder detects a magnetic proximity switch, when the piston has reached the front or rear end position. So that it triggers a signal with which the corresponding control valve interrupts or opens the supply of the working medium ( hydraulic fluid, compressed air).

Störlichtproblematik

An important source of interference for optical proximity switch is the flare of the sun or from artificial light sources such as fluorescent lamps, welding arcs, lightning. Your level is frequently subject to sharp fluctuations and significantly higher than the transmitted light level.

This can be remedied in many cases by optical modulation. Instead of a constant stream of light pulses of a predetermined frequency are emitted. The receiver evaluates only the pulses of this frequency and hides all superimposed disturbance from.