From OpenSCADAWiki
Regulation
The dynamic model-simulator itself may be unstable without control. For example, the parameter of the drum level does not have the self-regulation and goes to extremes in the case of the balance absence in the control parameters, which is typical of a pure integral. For this reason, as well as to create a self-sufficient simulator capable of operating autonomously and without the PLC as a regulator, an object was created for the regulators controller for the boiler simulator in accordance with the regulation schemes in Figure 2-4.