TABLE OF CONTENTS The advanced control projects with the largest benefits usually have made significant improvements in the basic regulatory control system. While advanced process control (APC) techniques can partially compensate for such limitations as missing measurements, excessive dead time, and poor signal-to-noise ratios, a solid foundation will provide the lowest total cost, greatest total benefit, and the longest lifecycle for the advanced control system. Deficiencies in the measurement and the final element can increase the time required for process testing and identification by a factor of 5 or more and can significantly reduce the improvement in process capacity and efficiency provided by APC.
The core of a solid foundation for advanced process control is good measurements and final elements. The measurement is the window into the process and must be able to provide an undistorted view of small changes in the process. The final element is the means of affecting the process and must be able to make small changes to the process. This overview provides a perspective of how these objectives are best met by reducing the reproducibility error, noise, and interferences in the measurement and decreasing the stick-slip and dead band in the control valve.
Reproducibility is the closeness of agreement of an output for an input approaching from either direction at the same operating conditions over a period of time. Repeatability is the closeness of agreement of an output for successive inputs approaching from the same direction at the same operating conditions. Reproducibility includes the repeatability...
