Interface modules (IM) 

Communications processors (CP); (for connecting to  PROFIBUS) 

Digital and analog modules are now called  “signal modules ” (SM) 

As in a real application, the S7-300 modules are plugged into the profiled rail on the basic plate, fastened and connected to each other via the rear panel bus to be system compatible。 The system is quickly and safely connected electrically to the inputs and outputs on the modules with the specific connector adapter。 Due to its construction, the system is open to future development (Dumitru)。 

4。3  The implementation of the fuzzy– PLC system 

SIMATIC Step 7 V6。2 software has been used for programming the PLC system。 Here, the required software to obtain the desired control over the system has been created using programming blocks。 It is obvious that the descriptions used in programming blocks also use the addresses obtained considering the hardware descriptions。 

The PLC application of the system has been performed by Fuzzy Control++ V5。0 software。 First of all, inputs and output membership functions and rule chart information are transferred into computer environment by using Fuzzy Control++ V5。0 software and prepared to be available for the control。 Further, these will be under control of an expert knowledge 

The Fuzzy Control++ consists of a software package that enables to implement good-quality, fully automatic control systems for processes。 

Processing is performed as follows: The instantaneous input values are translated into degrees of truth (“fuzzification”), logic operations are performed on the degrees of truth (“if” part of the rule), the degree of truth for the affected output is determined (the “Then” part of the rule, or the “inference”), and the numerical output value is calculated by weighting the resulting membership functions and computer centroid 

(“defuzzification”)。 

In Fuzzy Control++ V5。0 program, the separate input and output membership functions are formed as well as the symbolic representation of the rule base (figure 9)。 The triangle membership function has been preferred considering its simple structure and high efficiency at the calculations。 For the inputs, a triangle function clustered by three is used (figure 10, figure 11) and for the output five fixed valuable membership functions have been selected。 

Fig。 9: The input and output membership function and the symbolic representation of the rule base。 

Fig。 10: The input 1 formation of membership function 

Fig。 11: The input 2 formation of membership function 

The output membership function of the presented system has been derived as a singleton function (figure 13)。 

Fig。 12: The output formation of membership function 

The relation between input membership functions and output membership functions of the designed system has been shown in figure 13。 

Fig。 13: The rule table 

Fig。 14: The diagram of input and output membership function 

The “decision unit” which is one of the most important stages of fuzzy logic control can be named ”Fuzzy Engine”。 Fuzzy logic is the core part of the control。 It uses fuzzy concepts and it determines the required control by making inference (Cemal Yilmaz)。 

The resulting real control signal is applied to the system by the structure shown in Fig。 14。 Here, the control conection between fuzzy logic software and the field is supplied by FB30 Function Block and DB30 Data Block。 

Fig。 15: The application of fuzzy logic control 

The operating time of control system calculation in PLC application will be different according to the number of inputs, outputs, membership functions and rules。 The increase of the operating time will affect in negative way the performance of the system。 The decrease of the operating period depends on the speed of the hardware。