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 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 doorknobs 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[1]. Either a motion sensor or crash bar with an internal switch is used to unlock the door on the egress side of the door automatically.

Principle

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.

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.

Technical comparison

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.

Advantages

Remote operation: Magnetic locks can be turned on and off remotely by adjusting the power source.

Easy to install: Magnetic locks are generally easier to install than other locks since there are no interconnecting parts.

Quick to operate: Magnetic locks unlock instantly when the power is cut, allowing for quick release in comparison to other locks.

Sturdy: Magnetic locks may also suffer less damage from multiple blows than do conventional locks. If a magnetic lock is forced open with a crowbar, it will often do little or no damage to the door or lock. There are no moving parts in an electromagnetic lock to break.

Disadvantages

Requires a constant power source in order to be secure.

Can de-energize in the event of a power outage, disabling security.

Expensive in comparison to mechanical locks.

Requires additional hardware for safe operation.

Installation

The magnetic lock is suitable for both in-swinging and out-swinging doors. Brackets (L bracket, LZ bracket, U bracket) are used to orient the armature for use with both applications. Filler plates are also used to provide a large, flat mounting area on the door frame when the electromagnet is larger than the available mounting space on the door frame due to the frame's geometry.

The magnetic lock should always be installed on the secure side of the door. Most installations are surface mounted. For safety, magnetic lock, cables, and wires should be routed through the door frame or flush mount with wire mounting.

Installation is straightforward. With in-swinging applications, the electromagnet is typically installed in the opening corner of the door at the door's header. Maglocks can also be installed vertically in the door opening when they are furnished with a full-length housing. With this configuration, the armature is through-bolted through the door and oriented to mate with the face of the electromagnet. The armature plate and electromagnet must touch in order to provide locking holding force.

With out-swinging applications, the electromagnet is typically installed on the side of the door header. In this configuration, the armature is mounted on a Z shaped bracket that orients the armature to mate with the electromagnet.

Magnetic locks are almost always part of a complete electronic security system. Such a system may simply consist of an attached keycard reader or maybe more complex, involving connection to a central computer that monitors the building's security. Whatever the choice of locking system, fire safety is an important consideration.

Other variations and improvements on the electromagnetic locks have been developed. The most remarkable is the shear lock, where the armature does not directly pull off the face, but the load is instead in shear, like a mechanical stop. The shear magnetic lock allows a door to swing in both directions, as opposed to the original (and now ubiquitous) direct pull-type, which normally works either in an in-swing or out-swing configuration. In order to provide the shear magnetic lock with the appropriate holding force, then two pins lock the armature onto the magnet itself and ensure that the magnet locks into place.

Holding force

A magnetic lock has a metal plate surrounded by a coil of wire that can be magnetized. The number of coils determines the holding force which characterizes the lock:

Micro Size: 275 lbf (1,220 N)  holding force.

Mini Size: 650 lbf (2,900 N) holding force

Midi Size: 800 lbf (3,600 N) holding force

Standard Size: 1,200 lbf (5,300 N) holding force.

Shear Lock: 2,000 lbf (8,900 N) holding force

The standard size electromagnetic lock is used as a gate lock.

Application modes

For safety purposes, electric locks and electric strikes can be designed to operate in one of two modes:

Fail-safe – to protect people: The lock is released if power cuts off.

Fail-secure (also known as a non fail-safe) – to protect property: The lock remains closed if power cuts off. This type of lock has a cylinder, similar to those found in conventional locks. The cylinder makes it possible for the lock to remain secure, even if the power supply is cut off.

Electromagnetic locks are usually fail-safe and must satisfy applicable fire regulations so as to be safe in emergency situations.

Author: Written by Mr.Juan from S4A INDUSTRIAL CO.,LIMITED