was checked for any structural errors and an early prototype was presented to the customers. Figure 8.5 shows a test of the fuzzy logic system using simulated data as input. After the successful completion of the simulations the fuzzy logic was tested offline with real time data from the DCS. To do this the fuzzy logic control first was implemented on the OS/2 PC. The fuzzy controller than used real time DCS measurement values to generate set points values for the DCS. But during these offline simulations the DCS was only using the internal manual set points and not the fuzzy logic set points. By comparing the external fuzzy logic set points with the internal operator set points deviations between manual and automatic operation could be detected and if necessary eliminated. After the offline testing was finished successfully the online testing started. For the online tests the DCS activated the external set points and so the closed loop performance of the fuzzy logic controller could be tested. The fuzzy logic controller was optimized while running in the closed loop mode from the fuzzyTECH development tool on the WIN95 PC. To do this the OS/2 PC was connected with a serial cable to the WIN95 PC. This way the fuzzification, inference and defuzzification were visualized in fuzzyTECH. Modifications of the rule base or term definitions were also entered in fuzzyTECH and than send to the fuzzy logic controller on the OS/2 PC.