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Texas Department of Public Safety Security Alarm and Electronic Access License B05938
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Electro Magnetic Locks

An electromagnetic lock, magnetic lock, or maglock is a locking device that consists of an electromagnet and an armature plate. By attaching the electromagnet to the door frame and the armature plate to the door, a current passing through the electromagnet attracts the armature plate, holding the door shut. Unlike an electric strike a magnetic lock requires power to remain locked and is therefore not suitable for high security applications, because it is possible to bypass the lock by disrupting the power supply. However, electromagnetic locks are better for emergency exit doors, because they are less likely to fail to unlock. Nevertheless, the strength of today's magnetic locks compares well with that of conventional door locks and they cost less than conventional light bulbs to operate. Power supplies incorporating a trickle-charged lead-acid battery pack can be used to retain security for short-term power outages.

The first modern direct-pull electromagnetic lock was designed by S. I. Saphirstein in 1969 for initial installation on doors at the Montreal Forum. Fire concerns by local authorities in locking the doors at the Forum prompted management to find a locking solution that would be safe during a fire incident. Saphirstein initially proposed to use a linear stack of door holders to work as an electromagnetic lock. These door holders were traditionally used to hold doors open, but in this application Saphirstein believed that they could be packaged and adapted to work as a fail-safe 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.

Under difficult business conditions, Locknetics was later sold to the Ives Door Hardware company and later, resold to the Harrow company. Much later this division was then again sold to Ingersoll Rand Security Technologies. The division was recently closed and transferred to other divisions within Ingersoll Rand Security. Employees that were associated with activities at Locknetics, went on to form other electromagnetic lock companies, including Dynalock Corporation and Security Engineering Co. Saphirstein continued developing electromagnetic locking technologies at other companies he initiated including Dortronics (later purchased by Sag Harbor Industries), Delta Controls (first purchased by the Lori Lock Company and then later purchased by Hanchett Entry Systems) and Delt-Rex Door Controls, all of which were located in Connecticut. 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 U.S., Canada, and throughout Asia were later established to create additional product offerings for the direct-pull electromagnetic lock.

The principle behind a electromagnetic lock is the use of electromagnetism to lock a door when energized. The holding force should be collinear with the load, and the lock and armature plate should be face-to-face to achieve optimal operation.

The magnetic lock relies upon some of the basic concepts of electromagnetism. 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. This is because the internal magnetic domains of the material align with each other to greatly enhance the magnetic flux density.

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, the force of the lock is proportional to the square of the relative permeability of the magnetic core. Given the relative permeability of a material can vary from around 250 for cobalt to around 5000 for soft iron and 7000 for silicon-iron, the choice of magnetic core can therefore have an important impact upon the strength of a magnetic lock. Also relevant is the choice of current, number of loops and effective length of the electromagnet.

Magnetic locks possess a number of advantages over conventional locks and electric strikes. For example, their durability and quick operation can make them valuable in a high-traffic office environment where electronic authentication is necessary.