Fuzzy pid based Temperature Control of Electric Furnace for Glass Tempering Process

4.1. Simulation of PID controller
The simulation result of the closed loop system step response of continuous and discrete time 
controllers is shown in Figure 4.1. For discrete time controller the process and sensor transfer 
function is changed to their equivalent discrete form for simulation study.
As it is observed from the figure 4.1 the discrete controller achieves better transient response 
than the continuous equivalent. 
The discrete system transfer function model of a glass tempering furnace with PID controller is 
shown in Figure 3.3. This model was simulated in different PID tuning mechanisms using a 
MATLAB code presented in Appendix B. 

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Fuzzy PID Based Temperature Control of Electric Furnace for Glass Tempering Process
M.Sc. Thesis, Addis Ababa University, December 2016 
55 
The step response of the closed loop system with PID controller is shown in the Figure 4.2. 
Besides different tuning mechanism for PID controller like Ziegler-Nichols, Cohen-Coon, 
Integral of time-weighted absolute error (ITAE) both load point and set point changes and 
MATLAB/SIMULINK PID tuning is shown.
As it is observed from the figure, with the MATLAB/SIMULINK PID tuning extension tool box tuned 
PID controller the step response of the system gets decreased in percent overshoot & settling 
time, increased in rise time and the steady-state temperature error is zero. According to the 
design specifications, the allowable steady-state temperature error is ±5%. Therefore, the 
designed controller has met the desired specifications. 
Figure 4. 1Step response of continuous and discrete closed loop PID control system 
Figure 4. 2 Step response of closed loop system with different PID tuning mechanisms. 
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Step response of continuous and discrete closed loop PID control system
Time (seconds)
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plit
ud
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Continuous system ZN tuning
Discrate system ZN tuning
Discrete system tuned by MA TLA B/pid tuning tool box
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Step response of dif f renet PID controller tuning mechanism system
Time (seconds)
Am
pli
tud
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ZN tuning
Cohen-coon tuning
ITA E tuning load point
ITA E tuning set point
MA TLA B/SIMULINK PID tuning

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Fuzzy PID Based Temperature Control of Electric Furnace for Glass Tempering Process
M.Sc. Thesis, Addis Ababa University, December 2016 
56