Sequential Control of a Batch Process
Snapshot of the front panel of the simulator:
This simulator simulates a sequential control system for a simple batch process. A tank is filled with water. The water is then heated and stirred, and finally the heated water is discharged from ther tank.
The simulator is based on the following mathematical model of the process (the individual parameters are defined on the front panel of the simulator):
which is based on mass balance, and
which is based on energy balance. There is a time-delay in the temperature measurement.
A stirring motor is controlled by the control signal
The motor is assumed to ensure homogenuous thermal conditions in the water in the tank.
The control signals are
The measurements are
The aim of the tasks below is to develop a better understanding of sequential control, and using a state diagram.
Sequential control is crucial in many control applications, as in chemical batch processes.
A sequential control procedure can be represented graphically by one of the following two methods:
State diagrams and SFC are quite similar, as they have the same basic elements:
Controllers can be implemented using graphical programming of state diagrams or SFCs in proper programming tools. For example, state diagrams are supported by the State Diagram Toolkit in LabVIEW, and HiGraph in the Step 7 programming tools of Simatic PLCs, while SFC is supported by the GX IEC Developer programming tool of Mitsubishi FX2N PLCs.