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Solenoids > Application Examples: Solenoids Used as Electric Door Locks
Solenoids Used as Electric Door Locks
An application requirement was outlined to develop an electrically operated lock using a solenoid which would fit within an existing case design of a standard door, furniture lock system.

The solenoid had to be suitable for continuous operation on 8, 12, and 24 volts DC and also for short periods on AC, as is used with door telephone systems. For 12 VDC battery-operated systems, it was necessary to limit the solenoid current to 500mA maximum in order to maintain a reasonable battery life.

The lock must be of universal fitting for either inward or outward opening doors of either left or right hand, without any modifications. An automatic deadlock design is also required, so that it is immune to attack from devices such as the flexible strip. It must be of robust design, to withstand 200,000 operations, and to operate and release against a relatively high side pressure. The lock is used in conjunction with most types of key mechanisms which effect a mechanical override for access. Likewise, spring-loaded door furniture would provide a mechanical override for exit. The resistance of the lock to door closure must be kept minimum to eliminate the need for expensive and powerful door closure devices.

The STA Tubular solenoid was selected. The solenoid was manufactured without the mounting bushing in a push-type configuration, allowing it to fit within the existing case design. The locking actuation was achieved with a 3mm push rod extension in the energized position, from the flat face of the base without the threaded bush. Coils were designed for standard 12 and 24 VDC and low current battery supply. The final system design also allows for the inclusion of monitoring switches which can indicate the door and lock status. The range offers highly effective electric locks at a relatively low cost.

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