Application, design and mode of operation:
A proximity switch is a device which causes a switching action without physical contact. SCHMERSAL proximity switches respond to targets that come within the active range of their generated sensing fields. These units are completely self-contained, and house a field generator, amplifier, and other necessary circuitry to accomplish electronic switching.
The units are all solid state and have no moving parts that can wear out. The electronic switches are not susceptible to contact contamination, contact erosion, or material transfer as are mechanical switches.
Their service life, within their specified ratings, is virtually unlimited. The switching is insensitive to vibration, and is positive (full step function) without chatter, regardles of how slowly the target approaches or recedes from the sensor.
The oscillator resonant circuit, located in the proximity switch, uses an open core coil to help produce a concentrated high frequency electro-magnetic (RF) field, which emerges from the active surface of the sensor. If a metal target (e.g. metal) enters this field, eddy currents are induced. The floating induced eddy current draws energy from the LC circuit (L: coil, C: capacitor). The load on the oscillator circuit evokes a decrease in the oscillating amplitude. The oscillator is attenuated.
The decrease of the oscillating amplitude is converted into an electrical signal by the electronic circuit, which leads to a change of switching state of the proximity switch.
When the electric conductive material is removed from the inductive field, the pulse amplitude increases and via the electronic circuit the original switching position is recreated. The oscillator is unattenuated.
Along with the mechanically operated limit switches, magnetic reed switches (magnetically operated) have been constantly gaining increased importance. They can be regarded as a complement to the plunger, roller and turret head operated limit switches and as an important addition to electronic proximity switches.