Question

• The length of time between water level measurements/ control adjustments is DT. • If the water level drops to the bottom of the band, the controller drives the inlet valve to 100% open. • The valve stays 100% open until the water level reaches the top of the band. When the water level reaches the top of the band, the controller drives the inlet valve to the fully closed position. • The inlet valve remains fully closed until the water level once again drops to the bottom of the band. 1. Write a script that prompts the user for the required inputs. Simulate water level control for the following inputs:

Answer 1

Water level control systems are used to control the level and flow of water circulation systems for a variety of processes. The device that performs the controlling action is a valve which is attached to a controller whose main objective is to maintain a desired set point level as well as accept a new one desired by the control engineer.Fuzzy logic is widely used in the control of many processes, including that of the control of the water level in a tank.

DESIGN APPROACH

The system consists of a tank, a valve, a fuzzy logic controller, the inputs (level, rate) and the outputs (scopes).The tank system is modelled using SIMULINK and consists of two pipes; one flowing in and the other flowing out denoted by inflow and outflow respectively. The fuzzy controller controls the valve that changes the diameter of the inflow pipe but the outflow rate depends on the diameter of the outflow pipe (which is constant) and the pressure ( which depends on the level ) of the water. Thus, by keeping the water level at the desired set-point, we ensure that the tank works properly.

Water Level Control in a Tank PID(s) PID Controller Mux WATER TANK VALVE Mux2 S-Function SwitchSubsystem Mux tank 2 Sum1

The watertank design model, shown in the figure below, models a feedback loop for regulating the water level in a water tank. The Controller block contains the first-order compensator to be tuned.

The simulink model of the control system is

mdl = 'watertank_comp_design';

open_system(mdl);

Voltage for H 10-C- (++ Input Output Desired Water Level Controller Scope Water-Tank Systemm

The Water Tank subsystem models the water-tank dynamics. Water enters the tank from the top at a rate proportional to the voltage, V, applied to the pump. The water leaves through an opening in the tank base at a rate that is proportional to the square root of the water height, H, in the tank. The presence of the square root in the water flow rate makes the plant nonlinear.

Simulation

Simulate controller response with periodic changes in the setpoint of the water level. When you run the model, the Rule Viewer updates dynamically to show which rule the fuzzy controller is using to set the flow rate.

sim('sltankrule',100);

bdclose('sltankrule');