C++ Neural Networks and Fuzzy Logic: Preface

Designing a Fuzzy Logic Controller

A fuzzy logic controller diagram was shown in Chapter 3. Let us redraw it now and discuss a design example.

Refer to Figure 16.2. For the purpose of discussion, let us assume that this FLC controls a hot water heater.

The hot water heater has a knob, HeatKnob(0−10) on it to control the heating element power, the higher the

value, the hotter it gets, with a value of 0 indicating the heating element is turned off. There are two sensors in

the hot water heater, one to tell you the temperature of the water (TempSense), which varies from 0 to 125° C,

and the other to tell you the level of the water in the tank (LevelSense), which varies from 0 = empty to 10 =

full. Assume that there is an automatic flow control that determines how much cold water (at temperature 10°

C) flows into the tank from the main water supply; whenever the level of the water gets below 40, the flow

control turns on, and turns off when the level of the water gets above 95.

Figure 16.2

  Fuzzy control of a water heater.

The design objective can be stated as:

Keep the water temperature as close to 80° C as possible, in spite of changes in the water flowing out of