Limit switches are widely used in industrial automation to detect mechanical positions, control movement, and prevent equipment from exceeding its travel limits. Based on their operating principles, they are mainly divided into mechanical limit switches and proximity limit switches.
1. Mechanical Limit Switches
Mechanical limit switches control the position or travel of moving machinery. When a moving component reaches a preset position, the switch activates to stop, reverse, or change the movement of the equipment.
These switches generally consist of an actuator head, contact mechanism, and housing. Common types include plunger, roller, and snap-action switches.
Plunger-Type Limit Switches
A plunger-type switch operates similarly to a push button, but it is activated by a moving mechanical component rather than manually. When the component presses the plunger, the contacts change state. A spring restores the switch when the pressure is removed.
Roller-Type Limit Switches
Roller-type switches are activated when a moving component contacts the roller, causing the internal mechanism to operate the contacts. Some models automatically reset through a return spring, while others require reverse movement to reset.
Snap-Action Limit Switches
Snap-action switches use a spring mechanism to produce rapid contact switching when the actuator reaches a specific position. They feature short operating travel, low actuation force, and fast response.
Mechanical limit switches commonly use SPST, SPDT, or DPDT contact configurations, depending on the control requirements.
2. Proximity Limit Switches
Proximity limit switches detect objects without physical contact. They are commonly used for position detection, travel control, counting, speed measurement, liquid level monitoring, and automated production processes.
Compared with mechanical switches, they offer faster response, reduced mechanical wear, stable operation, and longer service life.
Common types include:
Magnetic Proximity Switches
Magnetic proximity switches use magnetic fields to activate internal sensing elements, such as reed contacts, and generate switching signals.
Differential-Coil Proximity Switches
These switches detect changes in magnetic fields and eddy currents when an object approaches the sensing area. The resulting signal difference triggers the switching action.
Capacitive Proximity Switches
Capacitive switches detect changes in capacitance caused by approaching objects. They can detect both metallic and non-metallic materials and are commonly used for object and level detection.
Hall-Effect Proximity Switches
Hall-effect switches convert magnetic field changes into electrical signals. Certain models provide a latching function, allowing the output state to remain unchanged until an opposite magnetic field is detected.
Ultrasonic Proximity Switches
Ultrasonic switches emit sound waves and detect reflected signals to identify nearby objects. They are suitable for detecting solids, liquids, and powders without direct contact.
Inductive Proximity Switches
Inductive switches generate a high-frequency electromagnetic field. When a metallic object approaches, induced eddy currents change the oscillator’s operation, producing a switching signal.
Magnetic proximity switches may use SPST or SPDT reed contacts, while electronic proximity sensors commonly feature two-wire or three-wire output configurations.
