Door 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.

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.

Electro door bolts - 

An electro bolt is a solenoid activated. The force to drive a bolt is inversly proportional to open circuit distance. They use a lot of current to acheive locking against the return spring, and constant  to hold it locked. A bolt driver module is essential for large solenoids. They can be made fail secure or fail open, but most are spring loaded to unlock.   

agnets 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.. 

Motorised locks - 

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. Automatin systems may need feedback to ensure the bolt is fully retracted before the door or gate begins to swing. Similarly the bolt control system needs to be sure the deadbolt is correctly aligned before it drives the bolt into its receptical.

Gate bolts

Gates present three locking problems. Outdoor applications are prey to weather issues, poor alignment, and high forces.

Locking magnets are affected by wet and dirt.  

e 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.

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. 

Wired audio intercoms

Basic audio intercoms are wired in alarm cable or Cat5 cable. The handsets use four cores, plus 1 for additional buttons handset used.  A Cat5 is sufficient for 1 or 2 button panels with a keypad. 

Various finishes are available. Modular panels may have over 20 call buttons. Allow an extra core of cable per call button over 2.

Wired video intercoms

 Most video monitors now connect to the entry panel by 2 wire. Cat5 cable is acceptable up to 50m, but a 2 core data cable should be used. The PSU and lock can use the same 2 core cable, though check the lock requirements for PSU. 

Various finishes are available. Modular panels may have over 20 call buttons. Each 2 wire monitors wires to the entry panel. On 2 wire digital bus systems, all components (except lock) can be wired together.

Some systems are able to separate the camera from the panel, or have an extra panel. This can give a better or more relevant view of the caller.

GSM - Wireless audio intercoms

GSM intercom panels are mobile phones built inside an entry panel. They need only a power supply. When the call button is pressed, it calls the stored number (the householder). If the landline is busy, or unobtainable, it calls a 2nd number, and even a third. Once connected, the householder can open the door or gate by pressing a prescribed key on their phone.

Various finishes are available. Modular panels on apartment blocks may have over 20 call buttons, each programmed to a different set of numbers. 

A unique feature of GSM intercoms is using caller ID as an access code. Friends and family who know the intercom's SIM card number only have to dial it to open the gate. The line is dropped as soon as the intercom recognises the caller.

IP - Wireless video intercoms

 IP intercoms are video systems using digital video, with the ability to display on a fixed house monitor or a smartphone. Smartphones at home will connect by wifi to the house network. When you are out, the smartphone connects to the world network using your internet data,facility.

A smartphone needs to have the relevant app installed to accept calls. There is no call charges except the roaming data use. The householder can open the door or gate by pressing a button on the app. Various finishes are available.