Sampled data can arise in several ways-for example, from manual samples taken from the process at reel change, from discontinuous instruments such as scanning basis weight gauges, also from digital computer control. Sampled data in contrast with continuous data have the problem of how sampling should be carried out. This is discussed in relation to the spectral characteristics of the variable. The superiority of sampled data control for dead time processes and the relation between sampled data control and statistical quality control are mentioned.
Sampled data control system analysis and synthesis is introduced. The z-transform and modified z-transform are included.
Direct digital control is introduced, using sampled data forms as well as PID analog controller replacement. The relative features of pulse amplitude, pulse width and of velocity and positional algorithms are reviewed, also the selection of the sampling interval. A few of the applications to pulp and paper are reviewed.