Guide to Reed Switches

Reed switches are small yet powerful components that play a crucial role in countless electronic and industrial applications. In this guide, we will explore the fundamentals of reed switches— what is a reed switch and how it works, their various types, and key considerations when choosing a reed switch for particular uses.

By the end, you'll have a thorough understanding of reed switches, their roles in different applications, and how reed relays function. We’ll also cover the distinctions between normally open, normally closed, and changeover reed switches, ensuring you’re equipped with all the necessary knowledge for making informed decisions.

A reed switch is a magnetically operated electrical switch that uses two or more ferromagnetic reeds as contacts, hermetically sealed within a small glass tube. These reeds are typically made from a nickel-iron alloy, known for its high magnetic sensitivity. Unlike traditional switches that rely on mechanical actuation, reed switches operate through the presence or absence of a magnetic field, enabling contactless operation.

The glass tube housing the reeds is often filled with an inert gas, like nitrogen, to prevent corrosion and enhance the switch’s reliability over extended use. This sealed design not only protects the reeds from environmental factors but also ensures their longevity in various demanding applications.

A reed switch operates through a straightforward mechanism driven by magnetism. Here's how it functions:

• Normally Open State: In its default state, the reeds are positioned slightly apart, creating an open circuit where electricity cannot flow.
• Magnetic Field Applied: When a magnetic field—generated by either a permanent magnet or an electromagnetic coil—is brought near the reed switch, the ferromagnetic reeds become magnetised. Their magnetic properties allow them to be attracted to each other.
• Contact Closure: The magnetic force overcomes the reeds’ natural spring tension, pulling them together. This closes the circuit, allowing electrical current to flow between the reeds.
• Magnetic Field Removed: When the magnetic field is removed, the reeds lose their magnetisation and spring back to their original open position, breaking the circuit and stopping the flow of electricity. This simple on-off action, triggered by the presence or absence of a magnetic field, is the fundamental principle behind how a reed switch works.

This contactless switching mechanism is precise, efficient, and reliable. It eliminates the wear and tear associated with mechanical switches, making reed switches particularly suitable for applications where durability and sensitivity are critical. They are widely used in security systems, industrial sensors, and home automation devices due to their ability to operate reliably in various environments.

The circuit symbol for a reed switch typically consists of two parallel lines, representing the reeds, enclosed within a rectangle that symbolises the protective glass tube. In some cases, a dashed or dotted line may accompany the symbol to indicate the presence of a magnetic field.

This standard representation is commonly used in circuit diagrams, providing engineers and designers with a clear understanding of how reed switches integrate into electronic systems. Its simplicity effectively conveys the switch's core components and operation, ensuring precision in design and implementation.

Reed switches combine reliability, efficiency, and versatility, making them essential components in numerous electronic applications. Below are the key benefits:

• Durability: Reed switches operate without direct physical contact between moving parts, resulting in minimal mechanical wear. This design ensures an extended operational lifespan, often rated for millions or even billions of cycles.
• Energy Efficiency: The low power requirements of reed switches make them ideal for energy-efficient designs, particularly in battery-powered devices. They operate effectively with minimal energy input, conserving power and supporting sustainable solutions.
• Noise-Free Operation: Unlike traditional mechanical switches, reed switches perform noiselessly, making them suitable for applications where quiet operation is a priority, such as medical devices, consumer electronics, and home automation systems.
• Wide Application Range: Thanks to their compact size, high reliability, and resistance to environmental factors like dust, moisture, and vibration, reed switches are widely used across industries. Applications include automotive systems, industrial automation, medical devices, and security systems.

These advantages make reed switches indispensable for engineers and designers seeking robust, low-maintenance, and cost-effective solutions for automation and sensing applications. Their long-standing reliability continues to make them a preferred choice, even in demanding or hazardous environments.

Reed switches come in various designs to meet the specific needs of different applications. Here are some common types:

• Arduino Reed Switches: Ideal for projects involving microcontrollers, these switches are commonly used in modules, counters, speedometers, and relays.
• Waterproof Reed Switch: Designed for environments where water and moisture are present, ensuring reliable performance in harsh conditions.
• Electric Reed Switch: Used in applications requiring direct electrical control, such as in high-voltage or high-current circuits.
• NC Reed Switch: Normally, closed reed switches maintain continuity when the magnetic field is absent, making them ideal for security systems and status monitoring.
• Magnetic Reed Switches: These are activated by magnetic fields and are used in various industrial and consumer electronic applications.
• Plastic Reed Switch: Offering durability and lightweight properties, these switches are often used in compact devices where size and weight are critical.
• High Current Reed Switch: Designed to handle larger currents and used in power-intensive applications.
• Encapsulated Reed Switch: Encased in a protective material for enhanced durability and resistance to environmental factors.
• Cylindrical Reed Switch: Featuring a cylindrical shape, these switches are used in applications where space-saving is essential.
• Bistable Reed Switch: Retains its state even after the magnetic field is removed, useful in memory storage and latching functions.
• Latching Reed Switch: Similar to bistable switches, but can switch back and forth between two states when exposed to alternating magnetic fields.
• Changeover Reed Switch: Offers both Normally Open (NO) and Normally Closed (NC) configurations, providing flexibility in circuit control.
• Hamlin Reed Switch: A trusted brand known for precision and reliability in reed switch manufacturing.
• Hall-effect Sensor: Works with reed switches to sense and respond to magnetic fields, often used in proximity detection and motion sensing.
• Mini and Micro Reed Switch: Designed for compact applications requiring smaller, precision switches.

These different types of reed switches offer a range of functionalities to suit various electronic and industrial needs, ensuring reliability and versatility across applications.

Reed switches are widely used across various industries due to their reliable and precise response to magnetic fields. Their versatility makes them indispensable in numerous industrial applications. Below are some key uses:

• Automotive Systems: Reed switches play a crucial role in automotive applications, including fluid gauges, door sensors, automatic braking systems, and speedometers. They help ensure safety, precision, and efficiency in vehicle operations.
• Security and Access Control: Reed switches are essential components in security systems, such as door and window sensors for monitoring unauthorised access. They are also used in tamper-proofing systems to trigger alarms when magnetic displacement occurs.
• Industrial Automation: Reed switches are integrated into flow rate measurement devices, level sensors, and other detection systems in industrial settings. These devices enhance automation processes by accurately detecting fluid levels, flow rates, and motion.
• Home Appliances: Reed switches are widely used in household appliances like dishwashers, washing machines, and showers. They contribute to safety features, such as auto shut-off functions and thermal cut-offs, ensuring the devices operate safely and efficiently.
• Consumer Electronics: From laptops and mobile phones to clamshell designs and protective cases, reed switches are utilised in devices for automatic power management. When used in clamshell designs, they help power down screens when lids are closed.
• Measurement and Environmental Sensing: Reed switches are critical in environmental monitoring applications, such as anemometers for measuring wind speed, ensuring accurate detection in scientific and industrial research.
• Proximity Sensing and Automation: Reed switches are employed in automatic doors and proximity sensors for lights in fridges and other automated systems. They facilitate seamless operations in automated environments.

These applications highlight the adaptability and dependability of reed switches, making them invaluable across various industrial and consumer fields.

When choosing the appropriate reed switch for a specific application, several factors must be considered to ensure optimal performance and reliability. RS Australia sources its reed switches from trusted brands like KEMET, Assemtech and Littelfuse, featuring various models and materials. Here are the key considerations of selecting the right reed switch:

1. Load Requirements:
   • Determine the voltage and current that will be switched during operation. This includes understanding the load characteristics, such as switching at high or low voltage and current levels.
2. Operational Life:
   • Assess how many operations the reed switch will be expected to handle over its lifetime. High-cycle applications require switches with longer lifespans, while low-cycle applications may use simpler models.
3. Size and Form Factor:
   • Consider the physical dimensions of the reed switch. Size constraints may dictate the choice between surface mount, through-hole, or other mounting types.
4. Environment and Mounting:
   • Evaluate the environmental conditions, including temperature, pressure, and potential exposure to corrosive materials. Also, ensure that the switch is suited for the intended mounting method (e.g., surface mount, PCB mounting).
5. Material and Coating:
   • For longevity and low-level switching, switches with ruthenium or iridium sputtered/plated materials are ideal.
   • For moderate voltage ranges (50V to 200V), switches like Philips, Coto, or Comus with sputtered ruthenium are recommended.
6. High Voltage and Current Applications:
   • For higher voltage requirements (above 200V up to 4000V), consider switches like OKI ORD2210V.
   • For voltages above 1000V and higher currents, hermetically sealed vacuum switches are the best choice.

Selecting the right reed switch requires a thorough understanding of the specific needs and conditions of the application. Often, conducting a life test with multiple reed switches is necessary to determine the most suitable option. Beyond reed switches, RS Australia provides a wide selection of electronic components, including proximity sensors, industrial connectors, and more, catering to diverse industrial and electronic needs.