Posted by Maureen VanDyke on | Comments Off on A Design Guide for Reed Switches
If you’ve ever used a laptop or a flip phone, you may have wondered how the screen goes dormant once you close the device. Or maybe you’re curious about why your tablet screen turns on every time you open its protective cover. At the heart of these functions is an ingenious device called a reed switch.
What is a reed switch? Reed switches open and close electrical circuits when subjected to magnetic fields. For example, laptops usually have magnets at the top of the screen and the bottom of the keyboard; when the laptop is open, the magnets are far apart from each other, but when it closes, the magnets connect, interrupting the electrical circuit powering the laptop and causing it to enter sleep mode.
Reed switches appear in a wide range of applications, ranging from pacemakers to automotive exhaust sensors to toy lightsabers. Below, we’ve outlined the technology involved in building reed switches, as well as some of their most common applications.
What Is a Reed Switch?
A reed switch is a type of electrical switch with a magnetic-based actuation method. It contains two or three thin and flexible metal wires or blades (i.e., reeds) that are either touching or positioned a few microns apart within a hermetically sealed glass housing. The reeds serve as the switch’s contacts. When the switch is brought in close proximity to a magnetic field, the contacts either move apart or together, depending on whether the switch has a normally closed or normally open design.
The idea for reed switches was first proposed by Leningrad Electrotechnical University professor V. Kovalenkov in 1922. In 1936, Walter B. Elwood of Bell Laboratories designed the first reed switch. By 1938, experimental reed switches were integrated into coaxial cables to switch the cable’s center conductor. In 1940, the first reed switches became available to the public. Today, reed switches find application in many devices and systems, such as mobile phones, industrial equipment, automotive systems, and computers.
How Do Reed Switches Work?
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In mechanical applications, electric currents only flow through closed circuits. When something breaks the circuit, the electric current flow ceases.
Reed switches contain two electrical contacts that, when joined, complete a circuit. These contacts are made from a ferromagnetic material, usually iron, that can be easily magnetized. Manufacturers coat switches with hardwearing metal for durability, and then they encase them in a thin glass tube or envelope filled with nitrogen or other inert gases such as helium, xenon, or argon to protect them from rust and contaminants. Depending on the switch’s design, these contacts either join or break apartunder the influence of outside magnet fields.
Reed switches come in two basic types: Normally Open and Normally Closed.
Normally Open Reed Switches
In a Normally Open reed switch design, the switch defaults to an open position, breaking the circuit. When an outside magnet approaches, it polarizes the two contacts, allowing them to attract each other and snap together. This closes the circuit, activating the electrical flow. When the outside magnet is removed, the stiff contacts spring back to their original position, thus breaking the circuit and halting the electrical current.
Normally Closed Reed Switches
Normally Closed reed switches operate on the same principle, except that the switch uses a built-in magnet to keep its two contacts in a polarized state. This means that the switch’s default position is to keep the circuit closed, allowing the electrical current to flow continuously. When an outside magnet with reversed polarity approaches, it cancels out the magnetic field of the built-in magnet. This causes the two contacts to lose polarity, and they spring apart from each other to their default, non-magnetized positions (where they would be in a Normally Open design). This breaks the circuit, stopping the electrical current.
How does the design of reed switches distinguish them from other types of magnetic switches? Several differentiating factors distinguish reed switches from their solid-state counterparts.
Hall effect switches combine a Hall-sensing element with circuitry to monitor and respond to the magnitude of a magnetic field. This means that Hall effect switches must have a continuous source of power to work effectively.
When additional circuitry is added to a reed switch or Hall effect switch, like triode AC devices (or Triacs for short) or transistors, they also require a continuous electrical current to effectively operate. All these switches differ from simple reed switches, which instead are a passive component that doesn’t require a constant power source to operate.
Reed switches are available in a variety of sizes as denoted by their contact ratings. Contact ratings can range from 3 VA to as high as 100 VA to accommodate a diverse array of switched load sizes.
Benefits of Using Reed Switches
Reed switches use much less power than other electronic switch alternatives. Their simple design also makes it much easier to test them out of circuit.
Reed switches come with a host of additional benefits, such as:
Reliability and durability
Reed switches’ straightforward designs mean that they malfunction less often than other circuits, and their protective casings ensure that they can function in a variety of environments. These factors mean that reed switches can operate effectively for decades. Because of this, they’re frequently employed in digital on/off applications like door-closure detectors. A reed switch can have a life spanning tens of millions of switching cycles.
Precision in magnetic sensitivity
Reed switches’ magnetic sensitivity switch points offer higher levels of precision compared with solid-state sensors. This makes reed switches the optimal choice for applications that operate in highly variable environments.
Solid-state switches generally come in one-size-fits-all formats. In contrast, due to the inherent simplicity of their design, you can easily customize reed switches to fit the specifications of each end product.
Engineers should determine the maximum switching current, voltage, and power that reed switch contacts can withstand. Contact arcing, or electrical discharge that crosses the gap between separated contacts, can damage the switching components and cause metal transfer, reducing the switch’s life span.
Engineers should also consider whether the reed switch will operate under AC or DC loads, what the minimum switching power will be, and whether the reed switch will fulfill its life expectancy under projected electrical loads.
Reed switches can operate in a variety of settings. However, it’s important to determine the likely environment for end product use and select the proper switches for the design accordingly.
Reed switches are most susceptible to shock and vibration along the axis on which the switching components move. If excessive mechanical shock is expected to occur regularly when the switch is put into use, care should be taken to choose an appropriately sized reed switch that can best hold up to expected impact. In extreme cases, it may be better to consider using a Hall effect switch as it does not employ any mechanical contacts in its solid-state design.
Engineers should carefully consider the possibility of contact with or influence from outside magnetic fields or ferrous materials. For example, will nearby coils, motors, or batteries disrupt the switch’s magnetic field? If so, this could lead to unpredictable behavior, and steps should be taken to remove any of these stray magnetic fields from the area where the switch is in use.
Life Expectancy of Reed Switches
Compared to other types of switches, the life expectancy for reed switches is considerably longer. Since the contacts experience a relatively small range of mechanical motion, they rarely succumb to material fatigue.
Operating voltage is the main factor that affects the overall lifespan of a reed switch. Most reed switches are engineered for use in relatively low currents.
Other factors that might affect life expectancy include:
DC vs. AC loads
Vibration and shock
Magnetic interference from other sources
The MagneLink Difference
Reed switches are elegant, versatile, and cost-effective solutions for many design dilemmas. At MagneLink, Inc., we provide high-quality custom magnetic reed switch solutions for clients across the country and around the world. Our customers have relied on our premier magnetic switch offerings for over 30 years.
If you’d like to learn more about our reed switch selection, contact us today. Once you experience the MagneLink difference, we’re sure that you won’t want to go anywhere else.
Posted by Maureen VanDyke on | Comments Off on How an Environment Affects a Magnetic Switch
A magnetic switch is a device that closes an electrical circuit when exposed to a magnetic field. The switch stays open until it’s impacted by magnetism. This switching mechanism is ideal for underwater deployment and conditions where electric sparking could trigger explosions or fires.
How Reed Switches Work in Different Environments
A magnetic reed switch can be used in a host of non-conventional, harsh conditions thanks to its inherent operational characteristics. For example, the device can maintain its magnetic sensitivity on exposure to shock and vibrations. It is a non-contact magnetic switch, making it suitable for use in hazardous locations, such as potentially explosive environments.
Hermetically sealed reed switches add to the safety of this electrical switch. Besides having simple circuitry, the magnetic sensor can detect a magnetic field while its contacts are safely contained in its hermetically sealed housing.
Several design factors impact the performance and operational continuity of a reed switch in a shock or vibration environment. These measures help prevent functional problems, such as:
False signal interference/responses
Tempering with the switches’ magnetic sensitivity
Breaking the glass capsule
Below are essential factors to consider when incorporating a magnetic reed switch into your design:
Temperature changes impact magnetism by either strengthening or weakening a magnet’s pulling force. Heating a magnet decreases its magnetism by ramping up the speed and irregularity of atomic movements within its structure. On the other hand, lowering the temperature of a magnet expands its magnetic field and boosts its force of attraction.
Similarly, reed switch magnetism is stronger at a lower temperature and weaker at a higher temperature. Sporadic atomic movements surge as operating conditions get hotter, which leads to misalignment of the magnetic field. A reed switch’s operating sensitivity to a magnetic field (pull-in) goes up as temperature increases.
Magnetic Field Optimization
Magnetic fields are most impacted by ferrous material. Ferrous materials or other stray magnetic fields can affect how well the magnetic reed switch performs.
To boost your magnetic field provided by the trigger magnet, it is best to avoid installing it directly on ferrous material, like iron. If the magnetic switch is being installed on ferrous material, the impact can be minimized by inserting a non-ferrous material between the magnetic switch and its mounting location. Such spacers made from plastic, rubber, or even wood can help in this way.
Shock and Vibration
Inside the hermetically sealed glass enclosure of the magnetic reed switch are mechanical contacts that either make or break the electrical connection along the circuit’s signal path. When exposed to excessive mechanical shock, these contacts can be displaced, which can affect the performance of the magnetic reed switch.
It is best to identify potential areas of concern with regard to shock and vibration of the magnetic switch. Taking efforts early in the design process to eliminate or minimize these factors will result in better switch performance in your design. Consider repositioning the switch to avoid potential impact while installed on equipment. Additional rubber padding at installation can also help absorb excessive vibrations.
The mechanical design of a switch impacts its susceptibility to shock damage. Models to consider are:
Reed Switches: This devices have magnetic contacts contained in a glass tube. These contacts can be affected by excessive mechanical shock.
Hall Switches: These sensors are contained in a semiconductor device. As a result, they are less prone to malfunction due to mechanical shock. However, Hall sensors do require power in order to operate properly.
Anti-Shock Protection Offered in MagneLink’s Switches
Layers of potting compound are used inside the magnetic sensor’s housing to encase the glass enclosure of the reed switch. This provides considerable levels of vibration protection. The anti-shock material absorbs most of the impact, protecting the fragile reed capsule from substantial damage in the event of a fall, vibration, or shock. It is still recommended to avoid and minimize the effects of mechanical shock and vibration when selecting how and where the magnetic switch will be installed on your equipment.
MagneLink: Your Trusted Supplier of Long-Lasting Non-Contact Magnetic Switches
MagneLink is a leading innovator of advanced magnetic switch solutions, including hall and reed switches. We take pride in delivering reliable, customized non-contact switches to satisfy specific requirements across diverse industries—from waste recycling and transportation to machine tool equipment. Our switches are built for a long functional life and to withstand the harshest operating conditions, including extreme temperature and humidity.
Posted by Maureen VanDyke on | Comments Off on Selecting a Magnetic Switch for Your Next Design
Magnetic switches, as their name suggests, are devices that allow or disallow the flow of current based on the presence of a magnetic field. There are several types of magnetic switches, each possessing specific characteristics that lend themselves to different applications. When designing or selecting a magnetic switch, it is essential that parameters such as application type, circuitry and power requirements, magnetic sensitivity, and operating environment are carefully taken into consideration.
The most common types of magnetic switches in use today are Reed switches, Hall effect switches, and Triac or Transistor switches.
Reed switches consist of a pair of overlapping, but slightly separated metal contacts hermetically sealed in a small glass tube. When a magnetic field is present, the contacts are drawn together, completing the circuit.
Hall Effect switches are so named because they use the Hall Effect Principle to detect the presence of a magnetic field. When current flowing through the conductor is exposed to a magnetic field in a perpendicular direction, a potential difference (voltage) is generated in a transverse direction across it, thus triggering the switch.
Triac and Transistor switches are similar semiconductor devices with the ability to regulate the flow of current in a circuit. A Triac or Transistor switch, when used with a Reed or Hall Effect device, is triggered by small currents and voltages and is used to control significantly larger currents and voltages in an electrical circuit. Of all three switches, Triac or Transistor switches are the best suited for switching larger, or inductive-type, loads.
Magnetic Switch Applications
The construction and operating principles of the different switches make each suitable for different applications—although there are instances where there may be some overlap.
Reed switches are highly sensitive to magnetic fields, customizable, and are relatively low-cost compared to other switches. These switches are commonly used in proximity or limit switch applications, such as security alarms, doors in household appliances, cell phones, and doors on vehicles or heavy machinery.
Hall Effect switches are semiconductor devices. As such, they have no mechanical contacts. This gives Hall Effect switches an advantage of being less prone to damage due to mechanical shock. Hall Effect switches are commonly used as limit switches in actuators which can be found in factory automation equipment, elevator cars or vehicles.
Triac or Transistor switches are the most complex of these switch types, as they add more circuitry to the switch. Triac switches are designed for switching and power control applications in AC voltage systems, whereas Transistor switches are designed for switching and power control applications in DC voltage systems. Both switches are robust, making them ideal for more heavy duty, higher-current switching applications. They are commonly used for controlling relays, motors, or other inductive type loads.
Circuitry, Electrical Current, and Power Load Requirements
The Reed switch is the only one of the three switches that is considered a “dry contact” switch, and as such, is not required to be powered at all times. Due to the simplicity of Reed switches, they can be tested out of their circuit with a simple ohmmeter. Reed switches carry the switched current of the circuit when they make contact. Therefore, it is important to choose a reed with the proper Contact Rating for the power draw in the circuit. Choosing too small of a reed for a design could lead to a shorter switch life.
Hall Effect switches are ideal for low-to-medium DC power applications. They do require constant power to be supplied in order to function properly. Therefore, these switches need to be tested under load.
Triac and Transistor switches are best suited for higher power loads in AC voltage or DC voltage environments, respectively. Like the Hall Effect switches, they also need to be tested under load.
Magnetic Fields & Sensitivity
When determining which switch is best suitable for your application, it is important to understand how exposure to magnetic fields will impact your chosen equipment.
Reed switches are mechanical devices, meaning they are subject to excessive mechanical shock from impacts or vibrations in your operation that can disrupt magnetic fields. Reed switches are available in varying magnetomotive forces, measured in Ampere-Turns (AT), to suit the needs of a variety of applications. The magnetic sensitivity of a Reed Switch may vary based on the size of the reed, surrounding environmental factors, and the strength of the magnetic field applied.
Hall Effect switches
Hall Effect switches are semiconductors rather than mechanical devices, making them less prone to the risks posed by mechanical shock. In addition, they offer more options for application configurations, as they are available as Omnipolar or Unipolar options. Omnipolar devices can detect either the North or South poles of a magnet, while Unipolar devices sense only one pole. The magnetic sensitivity of Hall Effect switches depends on the electric current applied and the type of magnetic field generated.
Triac or Transistor switches
The current-carrying capacity of Triac or Transistor switches may be increased by using them in conjunction with Reed or Hall Effect switches. Of note, the magnetic sensitivity and mechanical benefits and limitations of the Reed or Hall Effect device used in the switching circuit will still apply.
At MagneLink, we take steps to make sure our Reed, Hall Effect, and Triac and Transistor switches are as durable as possible. All our switches are protected inside a housing filled with potting material, improving the mechanical durability of our switches and protecting them from environmental contaminants such as dust, weather, washdowns, and more.
MagneLink, Inc. has been a leading supplier of reliable magnetic switches for over 25 years. During this time, we have helped numerous clients across a broad range of industries with their magnetic switching needs. Our diverse offering of switches ensures that we are able to meet your requirements—regardless of the application. In the event a client has a unique application, we also offer custom design services.
If you would like to learn more about our products or services and how they can improve your operation, feel free to email us or call our sales team at 1-800-638-0801.