What is a Limit Switch ?
Limit switches are electromechanical devices used in various applications to detect the presence or position of an object along a specific path or course.
They trigger an electrical or mechanical action when the object reaches a specific position, making them essential in machinery control and automated systems.
Limit Switches Features:
The main characteristics of limit switches are based on their design.
The limit switches are composed of a switching mechanism and an actuator.
The actuator can be a lever, roller, plunger or other component that responds to movements or position changes in the machine or equipment:
- Lever: It is one of the most common actuators. It can have different lengths and shapes, and its position changes with the movement of the object to which it is connected.
- Roller: A roller mounted on the actuator allows the switch to respond to pressure or linear movement on a surface. It is useful in applications where the moving object may slide against the roller.
- Plunger: It is an actuator that moves in or out in response to the movement of the object. It can be activated by pressure or direct contact.
- Spring: Some limit switches use springs as actuators. It can compress or release in response to movement, flipping the switch in the process.
- Ball Plunger: This type of actuator uses a ball instead of a plunger. The ball moves to activate the switch when it encounters resistance or pressure.
- Wobble Stick or Wobble Plate: It is a flat actuator that tilts or rotates in response to movement. It can be used in applications where a precise response to certain tilt angles is needed.
- Rod Spring: Similar to a plunger, it uses a rod that moves forward or backward in response to movement, applying pressure to the switch.
- Flexible Roller: Can be bent to fit specific shapes and surfaces on which it is installed. Provides improved adaptability.
- Hinge Lever: A hinge-shaped actuator that moves in a plane, similar to the action of a hinge on a door. It can be used in applications where angular movement is needed.
- Articulated Arm: Allows greater flexibility in the position of the actuator. It is useful in applications where multidirectional movement is required.
Some design considerations include environment and actuator type:
- Environment: Some limit switches are designed to withstand adverse conditions such as humidity, dust, or extreme temperatures.
- Actuator Type: The choice of type depends on the specific application and the type of movement being monitored.
Operation of Limit Switches
When the actuator reaches a predefined switching point, the switch performs an electrical action, such as opening or closing a circuit. These limit switches can have single or multi-contact action configurations.
Contact Types:
- Normally Open (NO): The circuit is open under normal conditions and closes when the actuator reaches the change point.
- Normally Closed (NC): The circuit is closed under normal conditions and opens when the actuator reaches the change point.
Common Applications:
- Industrial Automation: Used to control the movement of machinery and equipment in production lines.
- Home Appliances: Present in appliances like washing machines, dryers, and automatic opening and closing systems.
- Automatic Door and Window Systems: Detect the position of doors and windows to activate or deactivate automatic systems.
To explain how to use it, let's assume a machine on an assembly line. A limit switch could be installed so that when a component reaches a specific position, the switch activates, triggering an action such as stopping the machine or activating another process.
Advantages of Limit Switches:
- Reliability: Robust and reliable devices.
- Versatility: Adaptable to a wide range of applications and environments.
- Precision: Allows precise control of position.
Are there standard sizes for limit switches?
Yes, there are standard sizes for limit switches, and these standards are used to facilitate the manufacture, installation and replacement of these devices in various applications. Standard sizes can vary depending on industry standards and manufacturer preferences, but there are some commonalities.
Here are some typical standard dimensions and sizes for limit switches:
- General Dimensions:
- Height: Can vary, but it's common to find limit switches with heights between 40 mm and 100 mm.
- Width: Typical width can range from 20 mm to 50 mm.
- Length: Length can vary, generally in the range of 60 mm to 150 mm.
- Actuator Move Distance: The distance the actuator can move before activating the switch can vary by model and specific application.
- Mounting Types: Some limit switches are designed for surface mounting, while others are integrated more recessively into systems and machines.
- Connection Types: Limit switches can have different types of electrical connections, such as screw terminals, plug-in connectors, or quick connections.
- NEMA (National Electrical Manufacturers Association): In North America, limit switches often follow NEMA specifications. For example, NEMA 1, NEMA 4X, etc., indicate specific environmental resistance features.
- IP (Ingress Protection) Ratings: Internationally, the IP (Ingress Protection) rating is common. For example, IP67 indicates that the switch is resistant to dust and can be submerged in water up to a certain depth.
- Actuator Type: The actuator type (lever, roller, plunger, etc.) can influence the overall dimensions and shape of the switch.
It's essential to note that, although standards exist, variability in dimensions and specific features remains significant by brand and model. When selecting a limit switch for a particular application, it's crucial to review the specifications provided by the manufacturer and ensure it meets the specific requirements of the system or machine.
What Is the Ingress Protection (IP) Rating in a Limit Switch?
The Ingress Protection (IP) rating of a limit switch, as well as other materials and components, is a classification indicating its resistance to water, dust, and other contaminants. It is measured according to the international standard IEC 60529, which uses a two-letter code to indicate the IP rating.
The first letter of the code indicates the level of protection against water, while the second letter indicates the level of protection against dust.
Water Ingress Protection Grades:
- X: No special protection.
- IPX0: No protection against water.
- IPX1: Protected against vertically falling water droplets.
- IPX2: Protected against water splashes from any direction.
- IPX3: Protected against water sprays from any direction.
- IPX4: Protected against powerful water jets from any direction.
- IPX5: Protected against powerful water jets from any direction, even if the switch is in operation.
- IPX6: Protected against powerful water jets from any direction, even if the switch is in operation for an extended period.
- IPX7: Protected against temporary immersion in water up to 1 meter depth.
- IPX8: Protected against continuous immersion in water at a depth greater than 1 meter.
Dust Ingress Protection Grades:
- X: No special protection.
- IP00: No protection against dust.
- IP1X: Protected against the entry of solid particles up to 50 microns in diameter.
- IP2X: Protected against the entry of solid particles up to 12.5 microns in diameter.
- IP3X: Protected against the entry of solid particles up to 2.5 microns in diameter.
- IP4X: Protected against the entry of solid particles up to 1 mm in diameter.
- IP5X: Protected against dust entry.
For example, a limit switch with an IP65 protection rating is protected against powerful water jets from any direction, even when in operation, and against dust entry.
The IP rating of a limit switch is important for choosing the right one for a specific application. For instance, a limit switch to be used outdoors should have a water and dust protection rating.
Are There Non-Mechanical Limit Switches?
Yes, there are non-mechanical limit switches. These limit switches use electrical or electronic sensors to detect the position of an object. The most common types of non-mechanical limit switches include:
- Electromagnetic Limit Switches: Using a magnetic field to detect the position of an object. When the object approaches the limit switch, the magnetic field changes, activating a switch.
- Inductive Limit Switches: Use an electric field to detect the position of an object. When the object approaches the limit switch, the electric field changes, activating a switch.
- Capacitive Limit Switches: Use an electric field to detect the position of an object. When the object approaches the limit switch, the electric field changes, activating a switch.
- Photoelectric Limit Switches: Use a light beam to detect the position of an object. When the object interrupts the light beam, it activates a switch.
Non-mechanical limit switches have several advantages over mechanical ones. They are more reliable, durable, and resistant to contamination and wear. They are also more compact and lighter, making them ideal for applications where space is limited.
Some examples of applications where non-mechanical limit switches are used include:
- Industrial Automation: Used in machines and robots to detect the position of components and control their movement.
- Laboratory Equipment: Used in laboratory equipment to control the movement of components and ensure experiment accuracy.
- Medical Applications: Used in medical equipment to detect the position of components and ensure patient safety.
In summary, non-mechanical limit switches are a reliable and versatile option for applications where detecting the position of an object is necessary.
However, in reality, non-mechanical limit switches are commonly known as proximity sensors, photoelectric sensors, etc. At Electrónica Embajadores, we do not consider them part of this section alongside what is commonly known as a limit switch, and these are located in their corresponding section.