Operation and Technical Comparison
– Electromagnetic lock uses electromagnetism to lock a door when energized.
– Holding force should be collinear with the load.
– Lock and armature plate should be face-to-face for optimal operation.
– Current through loops of wire produces a magnetic field.
– Magnetic flux density is greatly enhanced when solenoid is wrapped around a ferromagnetic core.
– Magnetic locks have advantages over conventional locks and electric strikes.
– Durability and quick operation make them valuable in high-traffic office environments.
– Remote operation allows for easy on/off control.
– Easy installation due to absence of interconnecting parts.
– Quick release when power is cut.
Advantages and Disadvantages
Advantages:
– Remote operation: Magnetic locks can be turned on and off remotely.
– Easy to install: Magnetic locks have no interconnecting parts.
– Quick to operate: Magnetic locks unlock instantly when power is cut.
– Sturdy: Magnetic locks suffer less damage from multiple blows.
– No moving parts to break.
Disadvantages:
– Requires constant power source for security.
– Can de-energize during power outages, disabling security.
– Expensive compared to mechanical locks.
– Requires additional hardware for safe operation.
– Fire safety is an important consideration.
Installation and Holding Force
Installation:
– Magnetic lock suitable for both in-swinging and out-swinging doors.
– Brackets used to orient the armature for different applications.
– Filler plates provide large, flat mounting area on door frame.
– Surface mounted installation is common for safety.
– Armature plate and electromagnet must touch for locking holding force.
Holding Force:
– Magnetic lock’s holding force determined by number of coils.
– Micro Size: 275lbf (1,220N)
– Mini Size: 650lbf (2,900N)
– Midi Size: 800lbf (3,600N)
– Standard Size: 1,200lbf (5,300N)
– Shear Lock: 2,000lbf (8,900N)
Electrical Requirements and Fail-Safe vs Fail-Secure
Electrical requirements:
– Electromagnet lock operates on DC power, around 5-6W.
– Current varies between 0.5A (12VDC) and 0.25A (24VDC).
– UL mark verification recommended.
– Dual voltage specification of 12/24VDC.
– Full wave bridge rectifier used for AC power conversion.
Fail-safe vs fail-secure:
– Electric locking devices can be fail safe or fail secure.
– Fail-secure locks remain locked when power is lost.
– Fail-safe locks are unlocked when de-energized.
– Direct pull electromagnetic locks are inherently fail-safe.
– Strong magnetic flux keeps door locked even under stress.
Applications and History
Applications:
– High security applications
– Emergency exit doors with fire safety applications
– Cost-effective compared to conventional door locks
– Suitable for use with motion sensors or crash bars
– Additional release hardware installed in locking system
History:
– First modern direct-pull electromagnetic lock designed by Sumner Irving Saphirstein in 1969
– Initial installation on doors at the Montreal Forum
– Locknetics company established by Saphirstein to develop accessories and control circuits
– Locknetics later sold to Ives Door Hardware and then to Harrow company
– Division sold to Ingersoll Rand Security Technologies in 1999 and closed in 2007
References:
– Sadiku, M., Elements of Electromagnetics (3rd edition), Oxford University Press, 2001
– The Complete Book of Locks and Locksmithing (4th edition), Bill Phillips, McGraw-Hill Inc. 1995
– Geringer A. Geringer R. Geringer D., Electromagnetic Door Lock Device, U.S. Patent 4,826,223, May 2, 1989
– Magnetic Locks (PDF), electroautomation.co.uk, Retrieved 22 February 2022
– Code requirements for doors with access control, March 2013Sources: https://en.wikipedia.org/wiki/Electromagnetic_lock
