You are here : Control System Design  Index  Simulations  Tank Level  Part 2 Tank Level Tutorial  Part 2The JAVA applet below is a simulation of the above tank system. The controller used in the previous simulation (and this next one) was a simple SISO PI controller forming a loop around the height h_{2}. The controller parameters are k_{p} = 0.3 and k_{i} = 0.007. Pump 1 is given a constant voltage so that the flow into tank 1 is always f_{1} = 0.9347. There are two important physical limitations on the system: the tank heights cannot be more than 100% or less than 0% and the flow out of tank 2 cannot be negative (no water can be pumped into the tank) or more than 10% per second. Because of this saturation of the actuator, an antiwindup controller has been implemented (see Chapter 14). (Another limitation of the model is that h_{1} must always be larger than h_{2}, but this can be overcome by replacing
with
when h_{2} is larger, since in this case f_{12} will be negative.) The block diagram for the closed loop system is shown below:
As before, the graph has a vertical scale of 25% per division and a horizontal scale of 10 sec per division. It shows the setpoint (the orange trace), the actual h_{1} (the blue trace), the estimated h_{1} (the red trace) and the actual h_{2} (the green trace). Pressing the "Change Parameters" button allows you to change the same parameters as in the previous example plus the controller parameters. Designing a controller for both the tank heights will not be covered by this discussion, but you might like to try this interesting problem yourself.
