Process control, automatic characteristics

For this reason, microfluidic channels are usually designed with width of 100 pm or less, representing an efficient reactor for rapid mixing of fluids, transforming the stages of carrier fabrication into a self-assembly (nucleation, growth by aggregation, and stabilization after a characteristic time scale) in a well-controlled automatic process. 

Except for the typical support of spectroscopy by computers, the above-mentioned manipulation of spectra for an automatic recording as well as computerized devices are qualified to be used in process control with online data acquisition and inline control functions reacting to threshold parameters in automatic monitoring. In addition, computers are applied in library searches for similarities of the measured spectra by use of structural retrieval algorithms or neuronal nets. Even spectra in the UV/Vis are not characteristic, such libraries can be used to store calibration spectra, including disturbing factors [31,32]. 

Adaptive Control. An adaptive control strategy is one in which the controller characteristics, ie, the algorithm or the control parameters within it, are automatically adjusted for changes in the dynamic characteristics of the process itself (34). The incentives for an adaptive control strategy generally arise from two factors common in many process plants (/) the process and portions thereof are really nonlinear and (2) the process state, environment, and equipment s performance all vary over time. Because of these factors, the process gain and process time constants vary with process conditions, eg, flow rates and temperatures, and over time. Often such variations do not cause an unacceptable problem. In some instances, however, these variations do cause deterioration in control performance, and the controllers need to be retuned for the different conditions. 

Figure 8-39 illustrates the operating characteristics for a simulated manual and automatic control. In any specific case, the process engineer and the compressor design engineer must cooperate in establishing some of the needs for and capabilities of the compressor. 

An adaptive control system can automatically modify its behaviour according to the changes in the system dynamics and disturbances. They are applied especially to systems with non-linear and unsteady characteristics. There are a number of actual adaptive control systems. Programmed or scheduled adaptive control uses an auxiliary measured variable to identify different process phases for which the control parameters can be either programmed or scheduled. The "best" values of these parameters for each process state must be known a priori. Sometimes adaptive controllers are used to optimise two or more process outputs, by measuring the outputs and fitting the data with empirical functions. 

Many control problems can be better solved with a diaphragm controller. The function of the diaphragm controller (see Fig. 3.27) can be easily derived from that of a diaphragm vacuum gauge the blunt end of a tube or pipe is either closed off by means of an elastic rubber diaphragm (for reference pressure > process pressure) or released (for reference pressure < process pressure) so that in the latter case, a connection is established between the process side and the vacuum pump. This elegant and more or less automatic regulation system has excellent control characteristics (see Fig. 3.28). 

VARIABLE (Process). The quantity or characteristic that is the object of measurement in an instrumentation or automatic control system. Odier terms used include measurement variable, instrumentation variable, and process variable, The latter term is commonly used in the manufacturing industries, Numerous ways to classify variables have been proposed—by methods of measurement, by end-measurement objectives, and so on. One of the most convenient and meaningful classifications is the physical and/or chemical nature of the variable, as follows ... 

A system or controller which can adjust its parameters automatically in such a way as to compensate for variations in the characteristics of the process it controls is termed an adaptive system or adaptive controller. 

A precondition for automatically controlling the dyeing process is detailed knowledge of the characteristics of the fiber to be dyed, the dyes and auxiliaries to be used, and the equipment available. To assure level dyeing from the begin-... 

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