tailieunhanh - Automated Continuous Process Control Part 7

Tham khảo tài liệu 'automated continuous process control part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 7 3 2003 8 28 PM Page 110 110 RATIO OVERRIDE AND SELECTIVE CONTROL Figure Complete control scheme for reactor of Example . LS101 and the lowest selected as the set point to FC98. Under normal conditions TC100 will be selected. Only when the ratio of total water to stream A is above the set point to RC95 will the ratio controller reduce its output enough in an effort to cut the steam and thus be selected. Note the reset feedback signals to RC95 and TC100. Notice that the ratio of total water to stream A will be at or close to Y only after the liquid water flow has been reduced to zero that is the only water entering is the steam. Using this fact Fig. shows a simpler control scheme. In this case FA is multiplied by Y to obtain the maximum flow of water that could be fed FTWmax. This scheme is simpler because there is no need to tune a controller. The reader may want to write the software program to implement the scheme shown in Fig. . 5-6 SUMMARY In this chapter we have introduced the computation tools provided by manufacturers. An explanation for the need for scaling was given. A brief discussion of the significance and importance of field signals was also presented. We also presented the concepts and applications of ratio control override control and 7 3 2003 8 28 PM Page 111 REFERENCES 111 selective control. These techniques provide a realistic and simple method for improving process safety product quality and process operation. Finally the chapter concluded with three examples to provide some hints on the design of control schemes. REFERENCES 1. C. A. Smith and A. B. Corripio Principles and Practice of Automatic Process Control 2nd ed. Wiley New York 1997. 2. J. E. O Meara Oxygen trim for combustion control Instrumentation Technology March 1979. 3. T. J. Scheib and T. D. Russell Instrumentation cuts boiler fuel costs Instrumentation and Control Systems November 1981. 4. P. Congdon Control alternatives for industrial .