Last revised: January 10, 2025

Reed switches are magnetically actuated switches. They are typically manufactured with two ferromagnetic reeds (contact blades), which are sealed in a glass capsule. In the presence of a magnet, the blades (contacts) close.

Reed switch types are dry reed switch or mercury wetted reed switch. A dry reed switch contains ferromagnetic contact blades sealed in a glass container with an inert gas. In a mercury wetted reed switch, mercury is contact material for electrical circuit, mercury to mercury. The contacting faces are renewed by capillary action drawing a film of mercury over the surfaces of the constant switching members as the movable contact member is moved from one position to another. The center position on reed switches can be center gap or off center gap. The gap is the contact meeting of the switch.

Specifications

Important specifications for reed switches include pole and throw switch configurations, electrical specifications, physical dimensions and other features.

Pole and Throw Configurations

Pole and throw configurations for reed switches can be:

• Single pole single throw (SPST)
• Single pole double throw (SPDT)
• Double pole single throw (DPST)
• Double pole double throw (DPDT)

SPST is a switch that makes or breaks the connection of a single conductor in a single branch circuit. This switch typically has two terminals. It is commonly referred to as a "Single-Pole" Switch.

SPDT is a switch that makes or breaks the connection of a single conductor with either of two other single conductors. This switch typically has 3 terminals, and is commonly used in pairs and called a "Three-Way" switch.

DPST is a switch that makes or breaks the connection of two circuit conductors in a single branch circuit. This switch typically has four terminals.

DPDT is a switch that makes or breaks the connection of two conductors to two separate circuits. This switch typically has six terminals and is available in both momentary and maintained contact versions.

A normally open (NO) switch has contacts that are open or disconnected in their unactuated (normal) position. A normally closed (NC) switch has contacts that are closed or connected in their unactuated (normal) position.

Electrical Specifications

Important electrical switch specifications to consider when searching for reed switches include:

• Current rating
• AC voltage rating
• DC voltage rating
• Power rating

Dimensions

Important dimensions to consider include:

• Glass encapsulated length
• Total length including leads
• Diameter

Features

Common features for reed switches include hermetically sealed, CE certified, CSA certified, UL listed, and weather resistant or waterproof.

Reed Switches FAQs

What are the key features engineers should consider when selecting a reed switch for a specific project?

When selecting a reed switch for a specific project, engineers should consider several key features to ensure optimal performance and suitability for the application. Here are some important factors to consider:

Sensitivity and Activation

Reed switches are activated by a magnetic field, and their sensitivity is determined by the intensity of the magnetic field required to change the state of the contacts. This is influenced by the stiffness of the reed blades, the gap, and the overlap between the contacts.

The pull-in range, measured in Ampere Turns, indicates the sensitivity of the switch. A lower Ampere Turn value suggests higher sensitivity.

Environmental Suitability

Consider the environmental conditions where the reed switch will be used. Some reed switches are designed to perform reliably in wet and harsh environments, making them suitable for such conditions.

Physical Dimensions

Important dimensions include the glass encapsulated length, total length including leads, and diameter. These dimensions are crucial for ensuring the switch fits within the design constraints of the project.

Electrical Ratings

Check the AC and DC voltage ratings, as well as the power rating of the reed switch, to ensure compatibility with the electrical requirements of the application.

Design Flexibility

Some reed switches offer design flexibility, such as low-profile designs for space-constrained environments or specific shapes for particular applications.

Certifications and Features

Look for certifications such as CE, CSA, and UL listings, which can be important for compliance with industry standards. Additional features like hermetic sealing and weather resistance may also be relevant.

Application-Specific Requirements

Consider the specific application requirements, such as non-contact switching for proximity sensing or the ability to handle specific environmental challenges.

What are the environmental considerations for reed switches?

When considering the environmental suitability of reed switches for specific applications, several factors are important to ensure reliable performance under various conditions. Here are some key environmental considerations:

Harsh and Wet Environments

Some reed switches are specifically designed to perform reliably in wet and harsh environments. This makes them suitable for applications where exposure to moisture, dust, or other challenging conditions is expected.

Hermetic Sealing

Reed switches often feature hermetic sealing, which protects the internal components from environmental factors such as humidity and dust. This sealing helps maintain the switch's performance and longevity.

Weather Resistance

Weather-resistant or waterproof features are common in reed switches, allowing them to function effectively in outdoor or exposed environments. This is crucial for applications that require durability against environmental elements.

Non-Contact Switching

The non-contact nature of reed switches makes them particularly suitable for environments where mechanical wear and tear could be an issue. This feature ensures that the switch can operate reliably without direct physical contact, which is beneficial in harsh conditions.

Reliability in Challenging Conditions

Reed switches are designed to handle chemically active liquids, dust, and dirt, which can cause issues in other types of switches. Their sealed design helps prevent contact sticking or remaining open, ensuring reliable operation over time.

What are the electrical ratings of reed switches?

When considering the electrical ratings of reed switches, there are several important factors to take into account to ensure they meet the requirements of a specific application. Here are the key aspects:

Voltage Ratings

Reed switches have both AC and DC voltage ratings. These ratings indicate the maximum voltage the switch can handle safely without risk of damage or failure. For example, standard reed switches can handle up to 120 volts for both AC and DC applications.

Power Rating

The power rating of a reed switch is crucial as it defines the maximum power the switch can handle. This is typically measured in watts. For instance, some standard reed switches can handle up to 100 watts DC maximum.

Contact Material

The contact surfaces of reed switches are often made from materials like Tungsten, which are chosen for their ability to handle specific electrical loads and provide a low resistance electrical connection.

Sensitivity and Activation

Although not directly an electrical rating, the sensitivity of a reed switch, measured in Ampere Turns, affects how the switch is activated by a magnetic field. A lower Ampere Turn value indicates higher sensitivity, which can be important for applications requiring precise control.

What is the design flexibility of reed switches?

When discussing the design flexibility of reed switches, several aspects are important to consider, especially in the context of various applications and environments. Here are some key points:

Compact and Low-Profile Designs

Reed switches, such as the 59177 series, offer ultra-miniature and low-profile designs, which are beneficial for integration within space-constrained environments. This makes them suitable for applications where space is limited, such as in battery-powered devices and IoT applications.

Shape-Oriented and Size-Limited Applications

Some reed sensors, like the 59001 Reed Sensor, are specifically designed to address the challenges of size-limited applications. Their shape-oriented design allows them to fit into various form factors, making them versatile for different market needs, including small and large appliances, security systems, and factory automation.

Standard Assembly and Mounting

The design of certain reed switches allows for standard assembly mounting using typical pick-and-place machines. This feature facilitates ease of manufacturing and integration into existing production processes.

Non-Contact Switching

The non-contact nature of reed switches provides design flexibility by allowing them to operate reliably in environments where mechanical wear and tear could be an issue. This is particularly useful in harsh or wet environments.

Versatility Across Applications

Reed switches are used in a wide range of applications, from security and access control systems to metering and proximity sensing. Their design flexibility enables them to meet the diverse requirements of these applications, ensuring reliable performance across different conditions.

What are the applications of reed switches in security systems?

Reed switches are widely used in security systems due to their reliability, non-contact operation, and adaptability to various environmental conditions. Here are some key applications and features of reed switches in security systems:

Security and Access Control

Reed switches are commonly used in security and access control systems. Their ability to operate without direct physical contact makes them ideal for detecting the opening and closing of doors and windows, which is a fundamental aspect of security systems.

Non-Contact Switching

The non-contact nature of reed switches ensures that they can function reliably without mechanical wear and tear. This feature is particularly beneficial in security systems where long-term reliability is crucial.

Environmental Suitability

Reed switches are designed to perform well in various environmental conditions, including wet and harsh environments. This makes them suitable for outdoor security applications where exposure to the elements is a concern.

Design Flexibility

The compact and low-profile designs of certain reed switches, such as the 59177 series, allow for seamless integration into space-constrained environments, which is often a requirement in modern security systems.

Versatility Across Applications

Beyond traditional security applications, reed switches are also used in proximity sensing and access control, providing a versatile solution for various security needs.

What is the non-contact switching feature of reed switches?

The non-contact switching feature of reed switches is a significant advantage in various applications, particularly in environments where mechanical wear and tear could be an issue. Here are some key points about this feature:

Operation Without Physical Contact

Reed switches operate by using a magnetic field to change the state of the contacts, which means they do not require direct physical contact to function. This non-contact operation is beneficial in applications where minimizing mechanical wear is crucial.

Reliability in Harsh Environments

The non-contact nature of reed switches makes them particularly suitable for wet and harsh environments. They can function reliably without being affected by environmental factors such as moisture, dust, or chemically active liquids, which can cause issues in other types of switches.

Applications in Security Systems

In security systems, the non-contact switching feature is advantageous for detecting the opening and closing of doors and windows without the need for physical contact, ensuring long-term reliability and reducing maintenance needs.

Design Flexibility

The non-contact feature also contributes to the design flexibility of reed switches, allowing them to be used in a wide range of applications, including proximity sensing and access control, without the constraints of mechanical connections.

What is the role of reed switches in proximity sensing applications?

Reed switches play a crucial role in proximity sensing applications due to their unique features and operational characteristics. Here are some key aspects of their role in these applications:

Non-Contact Operation

Reed switches operate without requiring physical contact, which is beneficial in proximity sensing applications. This feature allows them to detect the presence or absence of an object based on its proximity to a magnetic field, without mechanical wear and tear.

Magnetic Activation

They are activated by a magnetic field, either from a permanent magnet or an electromagnet. This makes them suitable for applications where the detection of magnetic fields is necessary, such as in proximity sensors used in industrial automation and control systems.

Environmental Suitability

Reed switches are designed to function reliably in harsh and wet environments, making them ideal for outdoor or industrial proximity sensing applications where exposure to elements like moisture and dust is common.

Design Flexibility

The compact and versatile design of reed switches, such as the 59001 Reed Sensor, allows them to be integrated into various form factors and size-limited applications. This flexibility is particularly useful in proximity sensing where space constraints are a consideration.

Low Power Consumption

Reed switches do not require power to maintain their state, which makes them an excellent choice for battery-powered proximity sensing devices, enhancing energy efficiency.

Reed Switches Media Gallery

References

Electronics360—Littelfuse compact, D-shaped cylindrical reed sensor offers design flexibility for IoT proximity sensing applications

Electronics360—Common sense about sensors: 4 questions to ask before selecting sensors for your next design

Electronics360—Littelfuse launches ultra-miniature overmolded reed switch solution for space-constrained designs