Magnet Biasing Type
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 Road traffic control devices or In-road Warning Lights, are markers, signs and signal devices used to inform,
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Dec 1, 2020 |
Capsule Endoscopy Camera Activation using Reed Switches
Endoscopy Pill For most people, an endoscopy is extremely intrusive and uncomfortable. But, before a Gastroenterologist can fully
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Mar 18, 2024 |
Magnet Sensors for Securing Fire safety and Emergency Exits
Emergency Exit Building codes provide standards for the safety, welfare and general health of the personnel occupying the buildings.
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Nov 7, 2020 |
Reed Sensors in Electric Car Chargers
Electric Car Charging Station Electrical cars are designed to have a range of 250-300 kilometers on a full charge. To ensure that the
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Nov 7, 2020 |
Reed switches in Ferrous part detection
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
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Nov 7, 2020 |
Reed switches in Safety Vane applications
Conveyor Vane The automation industry depends on feeding systems which feed parts of different shapes into the assembly machine. The
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Nov 7, 2020 |
Reed switches in Model Train Tracks
Model Railway Today modelers create model railway layouts as a hobby, recreating real locations and periods throughout history. Railway
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Nov 7, 2020 |
Reed sensors in Emergency lamp holders
Emergency Lamps Emergency lamps are rechargeable battery powered lamp that automatically turn on when there is a mains power outage.
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Nov 7, 2020 |
Reed switches in Floor detection in Elevators and Lifts
Elevator Most people are aware of Elevators, or lifts, as they are called in certain areas of the world. The electrical motors in
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Nov 7, 2020 |
Reed sensors in Survival rafts and ELTs
Emergency Raft Survival rafts contain water sensors which trigger the compressed air cylinder to inflate the raft when dropped into the
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Nov 7, 2020 |
Reed sensors used in Fuel cap position sensing
Automobile fuel cap open A dashboard or an instrument panel located in front of the automobile driver and displays instrumentation and
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Nov 7, 2020 |
Reed switches in Seatbelt lock sensing
Seat Belt Lock Seat belts are vehicle safety device used to secure the occupants of a vehicle against harmful movement that may result
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Nov 7, 2020 |
Reed sensors in Central Locking of Cars with Remote Keys
Automobile Key Central locking allows the driver or front passenger to simultaneously lock or unlock all the doors of an automobile.
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Nov 7, 2020 |
Reed sensors in Telephone Hook and Handsets
Telephone Handset Even though the telephone hook was ubiquitous in the 80s and 90s even every home or office, it has been replaced with
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Mar 9, 2024 |
Vagus Nerve Stimulators Use Reed Sensors for Activation
Vagus Nerve Stimulator The Vagus nerve in the neck is one of the primary communication lines to the brain. For patients with epilepsy
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Mar 19, 2024 |