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

2.2.2 Indirect resistance heating furnace 
Indirect resistance heating, a heating element transfers heat to the material by radiation, 
convection and/or conduction. The element is made of a high-resistance material such as 
graphite, silicon carbide, or nickel chrome. Heating is usually done in a furnace, with a lining 
and interior that varies depending on the target material. Typical furnace linings are ceramic, 
brick, and fiber batting, while furnace interiors can be air, inert gas, or a vacuum.
Indirect resistance heating can also be done with an encased heater, in which the resistive 
element is encased in an insulator. The heater is placed in liquid that needs to be heated or 
close to a solid that requires heating. Numerous other types of resistance heating equipment 
are used throughout industry, including strip heaters, cartridge heaters, and tubular heaters[7].
2.3 Temperature control systems of resistance electric furnace
To produce the required quality of tempered glass the temperature of electric furnace should be 
controlled. There is different controller’s used in glass tempering industry. PI, PID, Fuzzy, Fuzzy-
PID, feedback linearization and sliding mode controllers are used. 
2.3.1 PID Controller
The PID controller is the most common form of feedback. It was an essential element of early 
governors and it became the standard tool when process control emerged in the 1940s [8-10] 
[13][14]. In process control today, more than 95% of the control loops are of PID type, most 
loops are actually PI control. PID controllers are today found in all areas where control is used. 
The controllers come in many different forms. There are standalone systems in boxes for one 
or a few loops, which are manufactured by the hundred thousands yearly. PID control is an 
important ingredient of a distributed control system. The controllers are also embedded in 
many special purpose control systems. PID control is often combined with logic, sequential 
functions, selectors, and simple function blocks to build the complicated automation systems 
used for energy production, transportation, and manufacturing. Many sophisticated control 
strategies, such as model predictive control, are also organized hierarchically. PID control is 
used at the lowest level; the multivariable controller gives the set points to the controllers at 
the lower level [16].
PID controllers have survived many changes in technology, from mechanics and pneumatics to 
microprocessors via electronic tubes, transistors, integrated circuits. The microprocessor has 
had a dramatic influence on the PID controller. Practically all PID controllers made today are 
based on
microprocessors. This has given opportunities to provide additional features like 
automatic tuning, gain scheduling, and continuous adaptation [8]. 

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