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Electromechanical controllers have been replaced by microprocessor boards, but they are still working on old elevators.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.
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.
The elevator takes one request at a time.
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.
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.