Patent ID: 7545620

Claim:
An access protection device for a physical area, said device comprising: a fixed part with at least one access opening; a movable part for each of the access opening for closing them; a tumbler device for each movable part; wherein said tumbler device comprises a magnetic circuit with a magnetizable yoke located on the movable part and an electromagnet which is closable by means of the yoke; a controller comprising a current regulator for regulating the locking force of said electromagnet, the controller also operably connected to a machine within the physical area; and a sensor that informs the controller of an operating state of the machine; wherein a first and a second value are preset for the current regulator, said current regulator periodically carrying out a controlled jump from the first to the second set value and measuring the time from the beginning of the controlled jump to the time at which the second set value is reached to determine whether the tumbler device provides an intended locking force and to determine whether the magnetic circuit is closed by the yoke; and wherein the controller is configured to control the locking force and the operation of the machine based on the information from the sensor and on whether the magnetic circuit is closed by the yoke; and wherein the time from the beginning of the controlled jump to the time at which the second set value is reached is at its minimum when the magnetic circuit is closed by the yoke.