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

Reed switches in seat belt locking system
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 come on until the product is installed, or for example, a type of sensing where it is not convenient to install an actuating magnet, or an application where a magnet cannot be used for actuation. Such situations require a normally closed function trigger that needs to change the state of a bi-stable or normally closed reed switch. This 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 Capsule Endoscopy

capsule endoscopy Endoscopy Pill Before a Gastroenterologist can fully diagnose for example, a patient's stomach problem, an endoscopy is recommended first. This...Continue reading ->

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...Continue reading ->

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 ->

Reed sensors in Emergency lamp holders

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

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 countries of the world. They...Continue reading ->

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...Continue reading ->

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...Continue reading ->

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...Continue reading ->

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...Continue reading ->

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...Continue reading ->