Six criteria are offered for the evaluation of the performance of process controllers. Classical techniques for the design of PID controllers and modern control theoretic techniques for controller design are reviewed. It is shown that modern optimal control algorithms often do not lead to useful controller designs. They are useful only as tools in heuristic design methods. Their main problem is sensitivity to the nature of the process transfer function and the lack of conservative design methods. The problems faced in developing better algorithms are outlined.
Filtering equations are derived for processes described by linear partial differential equations with known homogeneous boundary conditions. Both discrete-time and continuous-time measurements are treated. As in the case of linear systems with time delays, the filtering and variance equations become partial differential equations for processes with continuous measurements. A numerical solution to the nonlinear variance equation is obtained for a particular diffusion process.
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