Reed Relays and
Electronics India Limited
Manufacturer of Reed Switches, Reed Sensors and Reed-based products
Reed Relays and Electronics India Limited Incorporated in 1971

Magnet Biasing Type

Reed switches in seat belt locking system
Magnet Biasing type Vane application

Some special field applications, for the sake of circuit logic, security concerns, or a power saving necessity, require a sensing signal which is normally closed (on) to go off at certain times. This could be for example, a product which comes sealed with a battery inside that should not be used until the product is installed. Another example would be, a type of sensing where it is not convenient to install an actuating magnet and only a Ferro-magnetic vane can be used. Such applications can be classified as Magnet Biasing type Applications.

Such situations require a biasing type normally closed function trigger that needs to change the state of a bi-stable or normally closed reed switch. Normally closed or bi-stable Reed Switches are constructed by using a combination of a Reed Switch and a biasing magnet, near it. The biasing magnet keeps the Reed Switch in a closed state.

The “opening” of a normally closed Reed Switch is usually achieved by actuation with the opposite pole of magnet or by a ferro-magnetic shunt which comes in between the magnet and the reed switch. All Biasing type applications are also classified as position sensing applications but not all position sensing type applications use biasing magnets.

A basic normally open for Form A type of Reed Switch can be modified with an external magnet to work as a normally closed or a latching (bi-stable) device. The best method is to use a permanent magnet close to the reed switch to keep it “closed”, and to bring a larger magnet with an opposite polarity to “open” the reed switch. The same function can also be achieved by bringing a Ferro-magnetic part between the reed switch and the biasing magnet which will shunt the field away from the reed switch and “open” it.

As Reed Switches undergo a special heat treatment or annealing prior to assembly, it ensures that the magnetic remanence of the reed blades is extremely low. This helps in applications where the reed switch may need to be closed for months or years by ensuring that the blades spring back and open up as soon as the magnetic field is removed or shunted.

For such biasing type applications, it is also important that the release AT of the reed switches being used are within a tight tolerance of the Operate AT to maximize the production yield of the biased reed switches. The only care that needs to be taken when using biased reed switches is that the actuating magnet should not come closer than the actuating point where the reed switch opens as this could lead to a pole reversal which in reed switch parlance is called re-closure.

Example Applications

Reed Sensors in In-road Warning Lights

In-road Warning Lights In-road warning lights Road traffic control devices or In-road Warning Lights, are markers, signs and signal devices used to inform, Continue reading ->

Dec 1, 2020

Reed Switches and Reed Sensors in Capsule Endoscopy

capsule endoscopy Endoscopy Pill For most people, an endoscopy is extremely intrusive and uncomfortable. But, before a Gastroenterologist can fully Continue reading ->

Nov 6, 2020

Magnet Sensors for Securing Fire safety and Emergency Exits

fire safety exit Emergency Exit Building codes provide standards for the safety, welfare and general health of the personnel occupying the buildings. Continue reading ->

Nov 7, 2020

Reed Sensors in Electric Car Chargers

E-car charger Electric Car Charging Station Electrical cars are designed to have a range of 250-300 kilometers on a full charge. To ensure that the Continue reading ->

Nov 7, 2020

Reed switches in Ferrous part detection

Reed switches in pick and place unit Pick and Place Robot For a cost effective solution to be used in heave machine automation where magnets cannot be used due to the sheer Continue reading ->

Nov 7, 2020

Reed switches in Safety Vane applications

conveyor belt Conveyor Vane The automation industry depends on feeding systems which feed parts of different shapes into the assembly machine. The Continue reading ->

Nov 7, 2020

Reed switches in Model Train Tracks

Reed switches in signal moduling in model train track Model Railway Today modelers create model railway layouts as a hobby, recreating real locations and periods throughout history. Railway Continue reading ->

Nov 7, 2020

Reed sensors in Emergency lamp holders

Reed switches in emergency lamp Emergency Lamps Emergency lamps are rechargeable battery powered lamp that automatically turn on when there is a mains power outage. Continue reading ->

Nov 7, 2020

Reed switches in Floor detection in Elevators and Lifts

Reed switches in floor detection in lifts Elevator Most people are aware of Elevators, or lifts, as they are called in certain areas of the world. The electrical motors in Continue reading ->

Nov 7, 2020

Reed sensors in Survival rafts and ELTs

Reed switches in survival rafts Emergency Raft Survival rafts contain water sensors which trigger the compressed air cylinder to inflate the raft when dropped into the Continue reading ->

Nov 7, 2020

Reed sensors used in Fuel cap position sensing

Automobile Fuel cap Automobile fuel cap open A dashboard or an instrument panel located in front of the automobile driver and displays instrumentation and Continue reading ->

Nov 7, 2020

Reed switches in Seatbelt lock sensing

Reed switches in seat belt locking system Seat Belt Lock Seat belts are vehicle safety device used to secure the occupants of a vehicle against harmful movement that may result Continue reading ->

Nov 7, 2020

Reed sensors in Central Locking of Cars with Remote Keys

Reed switches in door sensors Automobile Key Central locking allows the driver or front passenger to simultaneously lock or unlock all the doors of an automobile. Continue reading ->

Nov 7, 2020

Reed sensors in Telephone Handsets

Reed switches in telephone hook switches Telephone Handset Even though the telephone was ubiquitous in the 80s and 90s even every home or office, it has been replaced with Continue reading ->

Nov 20, 2020

Reed switches in Vagus Nerve Stimulators

Vagus Nerve stimulator Vagus Nerve Stimulator The Vagus nerve in the neck is one of the primary communication lines to the brain. For patients with epilepsy Continue reading ->

Nov 6, 2020