16-07-2011, 04:03 PM
Presented by:
Mohit Ghawari
pH control technique using fuzzy.ppt (Size: 2.26 MB / Downloads: 223)
Fuzzy Logic
Fuzzy logic is a form of many-valued logic.
It can accept values from 0 to 1.
IF variable IS property THEN action.
Fuzzy logic and probabilistic logic are mathematically similar.
Fuzzy logic corresponds to "degrees of truth", while probabilistic logic corresponds to "probability, likelihood".
Fuzzy Controller
Different Sections of Fuzzy controller
Fuzzification Section
Rule Base
Inference Mechanism
Defuzzification Section
pH
It is negative of the logarithm of the hydrogen ion concentration, to the base 10. I.e., PH= -log 10 [H+]
It varies from 1 to 14, “1” being most acidic and “14” being most alkaline, and “7” being neutral.
pH paper can be used to indicate the pH value of the substance.
pH Control System
pH controller using fuzzy logic
pH controllers are widely used in Sugar Industries.
Raw sugarcane juice has approx. “5” pH value and it should be “7”.
This process is done by adding lime juice and passing sulphur dioxide gas.
Fuzzication Section
“PH” and “LFPD” are the input variables.
Find the numerical values of the membership function defined for that variable.
This value can be used by the inference mechanism to trigger the rules in the rule base.
The set point for the process is normally 7.
After Fuzzication
Membership function of pH
Membership function of LPFD
Rule Base
Rule base stores the different rules that are to be used according to the input.
These rules are either gathered from experienced human operator or from careful study of existing pH control systems.
Inference Mechanism
The inference mechanism employed in pH control is based on individual rule firing. Each rule is evaluated and overall decision is derived.
Output from this unit is given a degree of satisfaction.
Membership punction choosen here is symmetric.
Defuzzication Mechanism
The inference mechanism employed in pH control is based on individual rule firing. In this scheme, contribution of each rule is evaluated and overall decision is derived.
Sugar Industries Without Automatic pH Control
Manually it can be done in two ways:
In first method, the flow of SO2 is stopped and lime juice controls the pH value. It provides an accuracy of 6.9 to 7.2
In second method, lime juice is added to heated raw juice until its pH reaches 10 and then SO2 is passed. It provides an accuracy of 6.9 to 7.1.
pH is observed using pH indicator paper.
Sugar Industries With Automatic pH Control
To implement this controller many methods can be adopted.
It may be implemented using a PC, a microprocessor, or a microcontroller.
In PC, program can be written in high level language(like “c”) but in microprocessor if “c” language is used then an external compiler is to be used. Else assembly language can be used.
Using a Microcontroller
Microcontroller of PIC series is used.
PIC 16f73 microcontroller chip is used.
In addition, we are using an USART, input buffer, output latches, LCD Display.
Hardware Block Diagram
Merits and De-merits
The method of using rule base is more lucid and natural to people.
Fussy logic methods can be used for tuning of conventional PID controllers.
Since the fuzzy controllers have no mathematical model, it is difficult to analyse the system.
The working of the controller heavily depends on the judgement of the human expert who formulated the rules.
Mohit Ghawari
pH control technique using fuzzy.ppt (Size: 2.26 MB / Downloads: 223)
Fuzzy Logic
Fuzzy logic is a form of many-valued logic.
It can accept values from 0 to 1.
IF variable IS property THEN action.
Fuzzy logic and probabilistic logic are mathematically similar.
Fuzzy logic corresponds to "degrees of truth", while probabilistic logic corresponds to "probability, likelihood".
Fuzzy Controller
Different Sections of Fuzzy controller
Fuzzification Section
Rule Base
Inference Mechanism
Defuzzification Section
pH
It is negative of the logarithm of the hydrogen ion concentration, to the base 10. I.e., PH= -log 10 [H+]
It varies from 1 to 14, “1” being most acidic and “14” being most alkaline, and “7” being neutral.
pH paper can be used to indicate the pH value of the substance.
pH Control System
pH controller using fuzzy logic
pH controllers are widely used in Sugar Industries.
Raw sugarcane juice has approx. “5” pH value and it should be “7”.
This process is done by adding lime juice and passing sulphur dioxide gas.
Fuzzication Section
“PH” and “LFPD” are the input variables.
Find the numerical values of the membership function defined for that variable.
This value can be used by the inference mechanism to trigger the rules in the rule base.
The set point for the process is normally 7.
After Fuzzication
Membership function of pH
Membership function of LPFD
Rule Base
Rule base stores the different rules that are to be used according to the input.
These rules are either gathered from experienced human operator or from careful study of existing pH control systems.
Inference Mechanism
The inference mechanism employed in pH control is based on individual rule firing. Each rule is evaluated and overall decision is derived.
Output from this unit is given a degree of satisfaction.
Membership punction choosen here is symmetric.
Defuzzication Mechanism
The inference mechanism employed in pH control is based on individual rule firing. In this scheme, contribution of each rule is evaluated and overall decision is derived.
Sugar Industries Without Automatic pH Control
Manually it can be done in two ways:
In first method, the flow of SO2 is stopped and lime juice controls the pH value. It provides an accuracy of 6.9 to 7.2
In second method, lime juice is added to heated raw juice until its pH reaches 10 and then SO2 is passed. It provides an accuracy of 6.9 to 7.1.
pH is observed using pH indicator paper.
Sugar Industries With Automatic pH Control
To implement this controller many methods can be adopted.
It may be implemented using a PC, a microprocessor, or a microcontroller.
In PC, program can be written in high level language(like “c”) but in microprocessor if “c” language is used then an external compiler is to be used. Else assembly language can be used.
Using a Microcontroller
Microcontroller of PIC series is used.
PIC 16f73 microcontroller chip is used.
In addition, we are using an USART, input buffer, output latches, LCD Display.
Hardware Block Diagram
Merits and De-merits
The method of using rule base is more lucid and natural to people.
Fussy logic methods can be used for tuning of conventional PID controllers.
Since the fuzzy controllers have no mathematical model, it is difficult to analyse the system.
The working of the controller heavily depends on the judgement of the human expert who formulated the rules.