This is the third posting on highlights of Chapter 15, Process Simulation, in Control Loop Foundation – Batch and Continous Processes. In my March 14 and 21st postings on process simulation I addressed some of the some basics associated with the integration of process simulation into a control system. In this posting we will start to dig into implementing the process simulation.
When a control system is commissioned, the step response of a self-regulating process is often characterized as first order plus deadtime. Similarly, the deadtime and integrating gain are used to characterize the step response of an integrating process. So, it is appropriate that a process simulation be designed to duplicate the step response. For example, a filter block, a deadtime block and a multiplier block may be used to simulate the process deadtime, time constant and gain of a single input-single output (SISO) self-regulating process. Process noise may be added to the simulated process outputs using a signal generator block. For example, the FLOW_VALVE composite illustrated below uses this approach to simulate the makeup and reactor flow processes discussed in the March 21st posting. This composite was created using these standard function blocks.
Additional inputs may be included in the process simulation to address abnormal operating conditions. Outputs may also be included in the simulation to reflect abnormal conditions. The simulation of an integrating process may be implemented using a combination of standard function blocks and a calculation as illustrated below.
The real-time dynamic response of the simulated recycle tank and associated control modules will accurately reflect changes in the flow to the reactor and in the recycle tank inlet flow disturbance input that is defined in the recycle tank simulation module. Other examples that show process simulation may be explored on the ControlLoopFoundation web site.