Variables

Variables are the basis of every process visualisation. They contain data and information that is displayed directly to the operator or can be further processed by other system modules.

Data is recorded in the machine by various sensors, e.g. for temperature, pressure, contacts, etc.
Data is sent to the machine to control various actuators, e.g. heaters, motors, axes, etc.

These measured values from the machine are processed in the PLC
and used to control the machine.

The "Variables" system module exchanges the data using a communication component (e.g. driver, OPC server).

As a PLC is normally independent of a visualisation, the communication component must update this data from the PLC permanently/cyclically.
The system module automatically detects whether data has changed. Only then is this data sent to the user interface.
Inputs from the user interface are transferred to the PLC.
Other system modules can exchange data with the "Variables" system module for further processing. This can be the alarm system, for example, which monitors variables and may generate text messages for the operator.
However, higher-level systems can also dock onto the "Variables" system module for data exchange via standardised interfaces (OPC Classic or OPC-UA). These can be systems from the areas of MES (plant management level/control centre) or ERP (company level), for example.

In the user interface, control elements receive the data from the "Variables" system module and display it.
Some control elements allow input from the operator. The data then takes the reverse route through the components, possibly all the way down to the machine.