The exchange of data is automatically activated by a request from a visualisation application or a system server (e.g. alarm server) to the variable server. Visualisation applications register process variables for data exchange when, for example, a view is loaded on which variable values are displayed. If the form is unloaded, the registrations of the corresponding connected process variables with the variable server are cancelled. This also stops the data exchange.

System servers usually request the activation of data exchange for continuous monitoring purposes directly after initialisation. As long as a system server is running, the data exchange of the requested process variables remains active.

The data transfer is controlled via the status of a variable (see also parameter trigger variable).