Locking

Locking magnets

The essential elements of a locking magnet are a ferrous "C" core and a stator plate to complete the magnetic circuit. The two coils are usually isolated with a nominal  voltage of 12V. They can be wired in paralled for 12V supplies or wired in series for 24V supplies.

The magnet "C" core is set in a block of epoxy with an outer housing for fixing. The stator plate has a single central fixing that allows some tilting to ensure it mates perfectly with the magnet. A locating pin prevents the plate from rotating.  Holding force relies on a perfect mating. A piece of card between the magnet and stator can half the holding force.

Monitored magnets have a hall sensor measuring core flux. When the stator plate is in place and power is connected, the hall sensor indicates to a controller that the door is closed and secure.

Maglocks are poor on automated gates. Only good alignment of the armature plate will acheive the full holding force. Dust and rain can reduce holding force on outdoor applications.

Architectural magnets - 

Aluminium bodied magnets for internal doors, normally fixed to the door lintel. Attributes can include red/green monitor indicators, and internal delay on timers.  

Waterproof gate magnets - 

The "C" core is potted directling in a stainless steel housing. The cable is sealed in too. Hall sensors can be included, but indicators are not. Fixings are either through the magnet face, or thru a cross face axis. Waterproof magnets are string and reliable, but can collect surface dirt that reduces efficiency. 

Mortice magnets - 

Magnets designed to be set into a door frame or gate post. Some are just the block of epoxy with mounting ears attached. They have a high form factor and low price. Holding force may be determined by the fixings which are always in shear. Mortice magnet installations are always tidy.

Shear magnets - 

The main feature of the shear magnet is a spring loaded stator plate. When energised the magnet draws the plate into a socket. The security is then provided by the shear force of the plate in the magnet's socket. Alignment is critical. If the plate does not draw cleanly into the socket, there is no connection. The door force needs to be at 90 degrees to the holing force. 

Door strikes

Door strikes are fitted to the door frame. They are generally more secure than locking magnets, with higher holding force.

It is often a fire safety requirement that electrical door locking releases in an emergency. Electric strikes can be specified 'fail open' where the strike needs power to hold the strike locked. Fail open also unlocks the door if the power fails. 

Strikes are nearly always 12Vdc. AC versions will buzz naturally when energised, which helps advise the person when it is safe to push. This can be critical for lock strikes like dead bolts that are prone to jam under shear force.

Some strikes have a small sensor button in the rotating strike that prevents the strike re-locking when de-energised. These are used rarely for dead bolts. 

Some strikes are fitted with bolt monitors that warn if the bolt has not located properly, for example when a latch snib button has held the bolt back.

Night latch strikes - 

Strikes that fit to the back face of a door frame are popular on residential entrance doors. Also described as Yales latches or night latches, the latch bolts are spring loaded to auto-lock into the keep or strike.  Available in fail secure or fail open. Gate strikes are a particular kind of surface strike msd for wooden doors (see gate bolt selection).

Mortice strikes - 

Mortice strikes are embedded into the door frame. They mostly work with auto-retracting bolts which are also morticed into the door slam style. They are a tidy solution, and easy to engineer into the door and frame during manufacture. The are the default strike for aluminium doors which are manufactured to high tolerances, easy when you don't need to worry about wooden doors that can swell or warp. Available in fail secure, or fail unlocked on fire exit doors.

Motorised locks - 

The motorised lock replaces the spring latch. The motor drives a deadbolt into a fixed strike on the door frame. There is often a maget in the strike and a Hall sensor in the lock body to ensure the two are correctly aligned before the bolt is driven. Bolts can be longer than normal latches, and square for more strength. They are less susceptible to jamming when under pressure, as the motor is stronger than a release spring. The energy to release is often lower than a pulse on a solenoid, and the power does not need to be maintained to stay unlocked, both factors that make motorised locks suitable for battery operation.

Automated door bolts - 

Often used on automatic aluminium swing doors. These electro bolts use a small solenoid to hold the door locked (fail open). They can be made fail secure or fail open, but most are spring loaded to unlock. They need a hall sensor in the lock body to ensure the door and frame correctly aligned before the bolt is activated.  Most have built in release timers, so that a short release pulse keeps the bolt retracted for several seconds until the hall sensor in no longer aligned. This means a contant power supply as well as a lock trigger input. 

Gate & door bolts

Locking is essential to rural security as gate automation is relatively easily forced. Thieves target properties out of reach of security forces within an effective response time frame.  

Automated gates present three locking problems. Outdoor applications are prey to bad weather, poor alignment, and high forces. Locking magnets are affected by wet and dirt.

Specialist locks for automated gates are increasingly sophisticated and effective. 

Gate solenoid bolts - 

An electro bolt is solenoid activated. The force to drive a bolt is inversly proportional to the distance travelled, so takes a high initial current. Fail safe versions are insecure when the power is off. They use a lot of current to acheive locking against a return spring, but less to hold it in place. A bolt driver module is essential for large solenoids. Bolts are susceptible to jamming when under gate motor pressure if the gate is energised too early. Gate bolts have a microswitch to inform the gate controler when it can start. The gate bolt shown is fail secure with  key release. 

Motorised bolts - 

Long stroke applications need a motorised bolt. Almost any stroke length can be made, but it will take time for the bolt to run the full travel. A gate automation system may need feedback to know when the bolt is fully retracted before the door or gate begins to open. Motorised bolts are less likely to jam under pressure because the motor is stronger than a return spring or solenoid. Automated gates will rely on a fixed gate stop to ensure the bolt and socket are aligned. 

Gate and timber door locks - 

Automated gates have been fitted with lock releases designed for heavy wooden doors. They have a latch that locates into a gate post strike or a grond strike. The energy of the closing door or gate pushes the latch back against a spring to the locked position. The latch is mechanically held secure ready to fire (like cocking a hand gun). A 12Vdc pule is sent to the release solenoid that removes the mechanical hold, causing the spring to retract the bolt. It remains retracted until the gate is reclosed. 

Latch travel is only about 15mm. Alignment is difficult over any gate length, and easily forced open. The locks are susceptible to jamming when under gate motor pressure, to the extent that some gate automations include a reverse thrust to aid releasing.