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Elevator control system


In the link below you can see a relay logic control circuit of an elevator with manual doors. Basically an elevator control system consists of a power circuit and a low voltage control circuit. The power circuit supplies the lifting motor, while the control circuit supplies the relay coils, the door locking mechanism and the motor brake.

At the head of the schematic there are the safety switches. The over current protection switch cuts off the control circuit in case of insulation failure. For example, if two points of the door interlock series get in contact with the metal frame of the door, the interlock would be bypassed. In order to prevent this dangerous condition all metal parts of the elevator are connected to the negative pole of the control circuit, while the positive pole is cut by the safety switches.
Each exterior door features two iterlock switches. The first one allows the requests when the door is closed; the second one lets the elevator move if the door is locked.
The finals cut the control system if the elevator goes over an extreme floor. The car safety brake is a mechanical device that prevents the elevator from falling. It sticks the car to the rails if an hoist rope breaks and also works in combination with the over speed control system (governor).

When a request button is pressed the elevator takes the right direction due to a selector fixed in the shaft on each floor. A shape mounted on the car turns the the selector in the right position. On a modern elevator this job is done by an electronic system that takes signals from a proximity switch fixed on the car.

Control circuit schematic (pdf)