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Elevator controllers

The elevator control system is supposed to manage the operation of the equipment. It is connected to buttons, sensors and switches, actuators etc.
On early elevators the operator had to hold two directional buttons in order to bring the car to the requested floor.
Later a famous elevator company designed a semi-automatic control system: by releasing the button the elevator stopped at the nearest floor.
Full automatic control system, based on relay logic, was invented after the first global war. Electromechanical controllers have been replaced by microprocessor boards, but they are still working on old elevators.

In relay based control systems the position of the car is detected by direction selectors mounted in the shaft at each floor. Basically a direction selector is an exchange switch, turned by the car through a shape.

elevator controllers

In some cases selectors are turned by mechanical gears in the machine room; however the working principle is the same. When a floor button is pressed, the signal from the request relay is sent to the right direction contactor, depending on the position of the selector.
An elevator control system can be single or collective operation.
Single operation: The elevator takes one request at a time.
Collective operation: The control system takes multiple requests at once. In most cases there are two buttons at each floor. If you push, for example, the down exterior button, the elevator will pick up you during the down ride.

Multiple elevators
They share exterior requests, which are sent to the nearest car. Old control systems use two relays controlled by a network of resistors. Depending on the position of the cars and which exterior button is pressed, the relays are supplied with a bit different voltage, so one of them prevails.




Microprocessor control systems

They were introduced around 1980. Since they feature few mechanical parts, they need less maintenance and are energy friendly. The movement of the elevator is controlled by proximity sensors. Thanks to microprocessor technology we can reduce the cost of wiring by using bus communication. The possibility of using Programmable Logic Controllers (PLC) is another advantage of microprocessor technology. The working of a PLC based control system can be easily changed by modifying the source code.