Limit Switches
Limit switches are a contact proximity sensor device that consists of an actuator mechanically linked to a set of output contacts. When an object comes into contact with the actuator, the device operates the contacts to make or break an electrical connection.
Limit switches operate by using an actuator that, when engaged by an object, triggers the internal contacts to open or close the circuit. They come in various configurations, including single-pole single-throw (SPST), double-pole double-throw (DPDT), and more, allowing for versatile applications. Electrical limit switches are designed to handle a range of voltages, with maximum DC voltages up to 250V and AC voltages up to 600V, depending on the model. They can also support currents up to 10A, making them suitable for heavy-duty applications.
In addition to their electrical specifications, industrial limit switches are built with robust housing materials such as metal or high-strength plastic, ensuring durability in harsh environments. Many industrial limit switches have high IP ratings, like IP67 or IP68, providing excellent protection against dust and water ingress.
Limit Switch Makeup
Limit switches are made up of three key components:
- Actuator Head - The actuator is the part of the switch that makes physical contact with the object. In some limit switches, the actuator is attached to an operating head which translates a rotary, linear, or perpendicular motion to open or close the electrical contacts of the switch.
- Switch Body – The switch body is the component containing the electrical contact mechanism, the contacts within the body open or close the electrical circuit when the actuator is activated.
- Receptacle/Terminals - The component containing the terminal screws or screw/clamp assembly necessary for wiring purposes.
Normal State Configuration
The normal state configuration of limit switches refers to the position of the switch when no external force is applied to the actuator. This configuration is crucial as it determines the default electrical state — either normally open (NO) or normally closed (NC). Understanding the normal state is essential for designing circuits that require specific default behaviours.
For instance, industrial limit switches are often configured as normally closed to ensure that a system remains active until a specific condition is met, such as the engagement of a roller limit switch or a plunger limit switch. This setup enhances safety and reliability in various applications, from door limit switches in automated entry systems to heavy-duty limit switches in manufacturing environments.
Actuator Types
Limit switches are available with a wide range of actuator types. The type of actuator used can be determined by the mounting position, force required and objects to be detected.
Rotary Lever
With lever actuators, a cam or plate hits the end of the lever arm which in turn rotates a shaft and operates the contacts in the switch. The rotation may be spring returned (momentary) or maintained.
Plunger
Plunger types are best where short controlled machine movements are present or where mounting space does not permit a lever type.
Cat Whisker or Coil Spring
Longer actuators with a coil wire that can be moved/bent in multiple directions. Typically used in conveying applications to count objects as they pass by.
Forked
Used with maintained contacts, consisting of two roller levers. One roller will trip the switch and when the second is moved to the opposite direction it will reset the switch.
Industrial Applications of Limit Switches
Limit switches are crucial components in various industrial applications, providing precise control and safety in automated systems. They are used to detect the presence or absence of an object, ensure the proper operation of machinery, and prevent accidents.
Conveyor Systems
Industrial limit switches are used to detect the position of products on conveyor belts, ensuring proper alignment and sorting. For example, roller limit switches can halt the conveyor if an item is out of place.
Elevators
Limit switches are employed to determine the position of elevator cars, ensuring they stop accurately at each floor. Door limit switches ensure the doors open and close safely and correctly.
Packaging Machines
In packaging lines, limit switches monitor the position of items to ensure they are correctly placed for sealing and labelling. Plunger limit switches are often used to trigger machine operations at precise moments.
Robotic Arms
Robotic arms use limit switches to detect the limits of their movement, preventing overextension and potential damage. Lever limit switches help in controlling the arm's range of motion.
Safety Interlocks
Limit switches serve as safety interlocks in machinery, ensuring that certain conditions are met before operations begin. For example, spring-loaded limit switches can detect if a guard is in place before a machine starts.
Assembly Lines
In assembly lines, limit switches ensure that components are correctly positioned and assembled. Momentary limit switches are used to signal when a part is in place, allowing the next step in the process to proceed.
How to Order Limit Switches from RS
RS is a trusted supplier and distributor of limit switches, offering a wide range of high-quality products from leading brands such as RS PRO, ABB, and Eaton. Ordering limit switches from RS is a straightforward process, designed to ensure you find the perfect switch for your specific needs.
RS's website features comprehensive filtering options to streamline your search. You can easily narrow down your choices by selecting specific criteria such as actuator type, IP rating, AC/DC voltage, and housing type, ensuring you find a limit switch that perfectly matches your requirements.
Delivery Information for Australia
For efficient delivery of our limit switches and other products across Australia, we recommend placing your orders by 5 pm AEST on weekdays. RS provides next-business-day delivery for products available in our local inventory.
However, please note that deliveries to some remote areas might take longer. To explore our full range of delivery services, which include expedited same-day delivery and options for consolidated shipments, please refer to our delivery information page for detailed guidance.