Application, design and mode of operation: The proximity switch is an electronic command device. Compared to the mechanical limit switch, it features non-contact switching upon approach as well as an electronic, i.e. non-contact, operation.
As there are no wearable mechanical parts such as actuating mechanisms and contacts, the service life of a proximity switch is virtually unlimited. Contact burning and contact contamination caused by ambient influences cannot occur.
Electronic proximity switches function without noise, bounce and reaction. They are insensitive to vibration and shock. There is no unreliable contact as can occur with mechanical switches, e.g. actuation too low, switching current too slow, etc. There is no contact bounce when switching direct current.
The oscillator resonant circuit, located in the proximity switch, uses an open core coil to help produce a concentrated high frequency electromagnetic (RF) field, which emerges from the active surface of the sensor. If an electro-conductive 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. This leads to a change of the switching condition of the proximity switch.
When the electroconductive 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.
Application: Alongside mechanically operated limit switches, magnetic reed switches are enjoying an increase in importance. They are often used to complement limit switches with plungers, rollers and swivel levers and are considered an important link to non-contact and contactless limit switches.