What is a reed switch? A reed switch is an electromagnetic switch that is used to control the flow of electrical currents in a circuit. Reed switches are made from two or sometimes more ferrous reeds that are encased within small glass tube-like envelopes.
These envelopes then become magnetized when moved together or separate when a magnetic field is moved towards the switch. Effectively, when the two reeds are in contact, electricity can flow around the circuit operating a device.
Types of Reed Switch
There are two fundamental types, ‘normally open’ and ‘normally closed’. In a normally open switch, the switch consists of two reeds, made from ferrous material such as a nickel-iron alloy. These reeds are then positioned so that they are not touching.
However, when a magnet is moved near the switch it pulls the reeds together, completing the circuit. Once the magnet is removed the reeds return to their original position, breaking the circuit.
A normally closed switch works in the opposite way, when no magnetic field is present the reeds are in full contact. Therefore, the electric circuit is complete, and the device is ‘on’. However, when a magnet is moved close to the switch, the reeds repel, split apart, and break the circuit.
Advantages of Using Reed Switches
There are many advantages that reed switches provide within finished product designs. The relatively low cost and simple operation of magnetic-based reed switches allow for significant design flexibility.
In fact, magnetic-based reed switches, either as bare reeds, reed switch sensors, or reed switch/actuator sets, present a number of unique advantages within finished product designs, including:
- Simple and reliable reed switch sensing and actuation capabilities.
- Operated through a non-magnetic material.
- No supply of voltage.
- Durability and performance over the extended service life.
- Protected from atmospheric corrosion.
What Type of Magnets Are Used With Reed Switches
Without a magnet, reed switches are more or less redundant. However, introduce a magnetic field to the reed switch and the switch will spring into action. Magnets are an essential component in ensuring reed switches work successfully.
Both the size and type of magnet required will solely depend on the type and assembly of the reed switch. Reed switches can either be hidden or fixed within an assembly and still function with a magnet. Therefore, the distance between the magnet and the switch is a critical element. The wider the distance, the stronger the magnet will need to be to interact with the switch.
Any permanent magnet will work with a reed switch, but it is important to remember that different materials have different strengths and different-sized magnets produce different-sized magnetic fields.
Neodymium magnets are the strongest type of magnets commercially available, and therefore even tiny magnets can be effective. Selecting a magnet for a reed switch requires several factors to consider; shape, strength, switch sensitivity, distance, and the angle between the magnet and the switch.
Understanding this will allow you to determine the influence the magnet will have on the reed switch and the magnetic field that is formed. Although it is known that you cannot see lines of magnetism, it is known that they flow from north to south without ever crossing each other, as seen by the magnet representation below.
How Do You Use Reed Switches In Practice?
You have probably seen how a clamshell cell phone switches on and off when it is either open or closed. Well, a clamshell phone often has a closed reed switch in the lower part of the device and a magnet in the upper part.
So, when the device is opened, the reed switch and magnet are relatively far apart. The contacts on the reed switch are pushed together and the power flows through the phone. However, if you close the case, you swing the magnet close to the reed switch and that pushes apart the contacts inside the switch. A circuit inside the phone senses this and switches the power off in an orderly way.
Additionally, reed switches can primarily be found for proximity and sensing applications. They can be found in many alarm systems for sensing doors and windows when they are being opened or closed.
One of the main uses for reed switches that most people encounter every day is laptops. Ever wonder how your laptop knows when to switch your screen on and off? Well, when the screen is lowered, this is when the reed switch and magnets are in action – due to the interaction between the switch and the magnet, the device is aware of the proximity of the screen and reacts accordingly. Therefore, knowing when to turn your screen on and off!
Shop Neodymium Magnets:
