Electromagnetic lock
The holding force should be collinear with the load, and the lock and armature plate should be face-to-face to achieve optimal operation.
Essentially it consists of an electromagnet attracting a conductor with a force large enough to prevent the door from being opened.
In a more detailed examination, the device makes use of the fact that a current through one or more loops of wire (known as a solenoid) produces a magnetic field.
This works in free space, but if the solenoid is wrapped around a ferromagnetic core such as soft iron the effect of the field is greatly amplified.
Although the actual performance of a magnetic lock may differ substantially due to various losses (such as flux leakage between the electromagnet and the conductor), the equations give a good insight into what is necessary to produce a strong magnetic lock.
For example, their durability and quick operation can make them valuable in a high-traffic office environment where electronic authentication is necessary.
Maglocks can also be installed vertically in the door opening when they are furnished with a full length housing.
The armature plate and electromagnet must touch in order to provide locking holding force.
Such a system may simply consist of an attached keycard reader or may be more complex, involving connection to a central computer that monitors the building's security.
The device outlined in their designs was the same in principle as the modern magnetic lock consisting of an electromagnet and an armature plate.
Because the mating area of the electromagnet and armature is relatively large, the force created by the magnetic flux is strong enough to keep the door locked even under stress.
Despite this, by adding a magnetic bond sensor to the lock and by using a power supply that includes a battery backup capability, some specialized higher security applications can be implemented.
There are additional pieces of release hardware installed in a typical electromagnetic locking system.
The first modern direct-pull electromagnetic lock was designed by Sumner "Irving" Saphirstein in 1969[6][7][8] for initial installation on doors at the Montreal Forum.
Saphirstein initially proposed to use a linear stack of door holders to work as an electromagnetic lock.
After a successful prototype and installation at the Forum, Saphirstein continued evolving and improving the design and established the Locknetics company to develop accessories and control circuits for electromagnetic locks.
Employees that were associated with activities at Locknetics, went on to form other electromagnetic lock companies including the Dynalock Corporation.
Other engineers also left these companies to form their own manufacturing firms in electronic locking, including Highpower Security Products LLC in Meriden, Connecticut.
Many other firms in both the US, Canada, and throughout Asia were later established to create additional product offerings for the direct-pull electromagnetic lock.
