PLANT CONTROL

• Picture of the frontpanel of the simulator
• What is needed to run the the simulator? Read to get most recent information!
• Tips for using the simulator.
• The simulator: plant_control.exe (click to download). 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 simulated system

In this simulator a simple plant is simulated. The plant consists of two liquid tanks in series. The production rate is controlled by a flow control loop. The mass balance of each of the tanks are controlled by two level control loops.

Each of the tanks are integrators, dynamically. The model of tank 1 is

rA₁dh₁/dt = K₁u₁ - w_out

The model of tank 2 is

rA₂dh₂/dt = w_in - K₂u₂

where

w_out = w_in = w_SP (procution rate setpoint)

The simulator also implements sensor and subsequent scaling functions of each of level measurement signals. Also setpoint scaling is implemented. The sensor and scaling functions are availble at the front panel of the simulator.

The level controllers, LC1 and  LC2, are PID-controllers.

Aims

The aim of this simulator is to give an understanding of the behaviour of a process plant where the process flow and the mass balances are to be controlled.

Motivation

Industrial plants usually consist of one or more production lines which in turn consist of a number of unit process operations, e.g. reactors, heat exchangers, and separators, connected in series. It is important that the production rate of the process line and that the mass balance of the individual processes are controlled. This is done principally as in the present simulator.

Tasks

1. Open loop control: Show (by simulation) that the tank levels can not be controlled in open loop (fixed control signal). (Tips: Set the controllers in manual mode, and change the production rate setpoint a little (this change is a disturbance to the tanks).

    

2. Closed loop level control with P-controller: You can let the level controllers LC1 and LC2 have P controller actions with gains of 0.2. (It is not focus on controller tuning in this simulator. The simulator Buffertank focuses on tuning level controllers).
   1. Explain that LC2 must have negative controller gain, while LC1 must have positive controller gain. Run the simulator. What happens if you give the gain in LC1 or in LC2 wrong sign?
   2. Show in a simulation that there is a non-zero steady-state control error in one of the tanks after a change in the production rate (which acts as a disturbance).

    

3. Closed loop control with PI-controller:  Let Kp and Ti in both LC1 and LC2 have values 0.2 and 5 [min] respectively.
   1. Show in a simulation that the steady-state level control errors are zero after a change in the production rate (i.e. a disturbance change).
   2. Show in a simulation that e.g. control loop 1 gets worse stability if the integral action is increased (Ti decreased).

[KYBSIM] [TechTeach]

Updated April 5, 2004. Developed by Finn Haugen. E-mail: finn@techteach.no.