Sequential Control of a Batch Process

Snapshot of the front panel of the simulator:

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• Tips for using the simulator.
• The simulator: sequential_control.exe . The simulator runs immediately after the download by clicking Open in the download window. Alternatively, you can first save a copy of the exe-file on any directory (folder) on your PC and then run the exe-file, which starts 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):

dh/dt=(1/rho)*(1/A)*[K_in*u_valve_in-K_out*u_valve_out]

which is based on mass balance, and

dT/dt=[1/(c*rho*A*h)]*[K_heat*u_heat+(T_in-T)*c*w_in+(T_env-T)*U]

which is based on energy balance. There is a time-delay in the temperature measurement.

A stirring motor is controlled by the control signal

u_motor

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

Aim

The aim of the tasks below is to develop a better understanding of sequential control using a sequential function chart (SFC).

Motivation

Sequential control is crucial in many control applications, as in chemical batch processes.

A sequential control procedure may be represented graphically with a sequential function chart (SFC).

SFCs have the following 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 e.g. the SFC programming language defined in the standard IEC 61131-3, which is implemented in e.g. the Codesys PLC programming tool (free).

Tasks

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.

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Updated 24 Sept 2026. Developed by Finn Haugen. E-mail: finn@techteach.no.