CD Controls Have Unique Problems: They Need Unique Troubleshooting Tools, 1998 Process Control, Electrical & Info. Conference Proceedings

Control System performance or lack of performance is an important factor in the search for optimum process operation. Much attention has been directed over the last few years towards performance monitoring and troubleshooting of single control loops. Packages are now available for real-time monitoring. How much help are these for CD controls? The answer is: probably not much. CD controls have their own unique problems which require unique tools for diagnostic troubleshooting. These problems arise due to the spatial dimension of CD controls. Among the CD specific problems are:

· The controllability of the CD variation is a function of the wavelength content of the signal and its position across the sheet. Conventional Fourier analysis does not provide this information.

· Most CD controls “map” measurement databoxes to actuators. Mapping creates errors which are associated with the occurrence of undesirable standing-wave instabilities across the sheet.

The paper will discuss available diagnostic methods for these and related CD control problems.