Sequential Control of a Batch Process

Snapshot of the front panel of the simulator:

Description of the system to be simulated

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

  • u_valve_in (boolean, i.e. having value TRUE or FALSE, or ON or OFF)

  • u_valve_out (boolean)

  • u_motor (boolean)

  • u_heat (continuous having any value between 0% and 100%)

The measurements are

  • Temperature T of the water in the tank

  • Level h of the water in the tank


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:

  • A state diagram
  • A sequential function chart (SFC)

State diagrams and SFC are quite similar, as they have the same basic elements:

  • States with actions to be executed when the state is active
  • Transitions from one active state to another taking place if the transition condition is logically true.

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.


  1. Run the simulator, and make sure you understand how the control system works.
  2. Draw a detailed SFC of the sequential control system (draw without looking at the SFC available from the front panel of the simulator). The actions in every state must be defined, and the transition conditions in every transition must be defined. For your information: Introduction to state diagrams.

[SimView] [TechTeach]

Updated 8. March 2009. Developed by Finn Haugen. E-mail: