Electromagnetic lock

An electromagnetic lock, magnetic lock, or maglock is a locking device that consists of an electromagnet and an armature plate. There are two main types of electric locking devices. Locking devices can be either 'fail safe' or 'fail secure'. A fail-secure locking device remains locked when power is lost. Fail-safe locking devices are unlocked when de-energized. Direct pull electromagnetic locks are inherently fail-safe. Typically the electromagnet portion of the lock is attached to the door frame and a mating armature plate is attached to the door. The two components are in contact when the door is closed. When the electromagnet is energized, a current passing through the electromagnet creates a magnetic flux that causes the armature plate to attract to the electromagnet, creating a locking action. 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. An electromagnetic lock, magnetic lock, or maglock is a locking device that consists of an electromagnet and an armature plate. There are two main types of electric locking devices. Locking devices can be either 'fail safe' or 'fail secure'. A fail-secure locking device remains locked when power is lost. Fail-safe locking devices are unlocked when de-energized. Direct pull electromagnetic locks are inherently fail-safe. Typically the electromagnet portion of the lock is attached to the door frame and a mating armature plate is attached to the door. The two components are in contact when the door is closed. When the electromagnet is energized, a current passing through the electromagnet creates a magnetic flux that causes the armature plate to attract to the electromagnet, creating a locking action. 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. Typical single door electromagnetic locks are offered in both 600 lbs. (2669 N) and 1200 lbs. (5338 N) dynamic holding force capacities. A 'fail safe' magnetic lock requires power to remain locked and typically is not suitable for high security applications because it is possible to disable the lock by disrupting the power supply. 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. Electromagnetic locks are well suited for use on emergency exit doors that have fire safety applications because they have no moving parts and are therefore less likely to fail than other types of electric locks, such as electric strikes. 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. There are additional pieces of release hardware installed in a typical electromagnetic locking system. Since electromagnetic locks do not interact with levers or door knobs on a door, typically a separate release button that cuts the lock power supply is mounted near the door. This button usually has a timer that, once the button is pressed, keeps the lock unlocked for either 15 or 30 seconds in accordance with NFPA fire codes. Additionally a second release is required by fire code. Either a motion sensor or crash bar with internal switch is used to unlock the door on the egress side of the door automatically. The first modern direct-pull electromagnetic lock was designed by Sumner 'Irving' 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 in 1999. The division was recently closed in 2007 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 the Dynalock Corporation. 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 an 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. Using the Biot–Savart law, it can be shown that the magnetic flux density B {displaystyle B} induced by a solenoid of effective length l {displaystyle l} with a current I {displaystyle I} through N {displaystyle N} loops is given by the equation: