Closed loop techniques

Prediction from In Situ Absorption Rate Constant Determined with Closed Loop Techniques... 

In 1942, Ziegler and Nichols [1] changed controller tuning from an art to a science by developing their open-loop step function analysis technique. They also developed a closed-loop technique, which is described in the next section on constant cycling methods. 

The closed-loop technique of Ziegler and Nichols [6] is a technique that is conunonly used to determine the two important system constants ultimate period and ultimate gain. It was one of the first tuning techniques to be widely adopted. 

The Ziegler-Nichols closed-loop technique is also useful, but more aggressive than ATV. 

One alternative to dynamic headspace is the closed loop headspace collection device, developed by Brunke et al. (9), shown in Fig. 4. This device places a flower within a collection vessel, and the volatiles are collected on an appropriate trapping material. The difference between this method and conventional dynamic headspace is that the closed loop technique constantly circulates the air within the device using an in-line pump. Results obtained with the closed loop system are similar to those obtained with conventional dynamic head-space. 

With years of research and development in the field of static drives, it is now possible to identify and separate the.se two parameters (f, and /, ) and vary them individually, as in a d.c. machine, to achieve extremely accurate speed control, even slightly better than in d.c. machines. In d.c. machines the armature current and the field strength arc also varied independently. A.C. machines can now be used to provide very precise speed control, as accurate as 0.001% of the set speed, with closed-loop feedback controls. This technique of speed control is termed I ield-oriented control (FOC) and is discussed below. 

C. M. Grill, Closed-loop recycling with periodic intra-profile injection a new binary preparative cliromatograpliic technique , J. Chromatogr. 796 101 -113 (1998). 

The identification of plant models has traditionally been done in the open-loop mode. The desire to minimize the production of the off-spec product during an open-loop identification test and to avoid the unstable open-loop dynamics of certain systems has increased the need to develop methodologies suitable for the system identification. Open-loop identification techniques are not directly applicable to closed-loop data due to correlation between process input (i.e., controller output) and unmeasured disturbances. Based on Prediction Error Method (PEM), several closed-loop identification methods have been presented Direct, Indirect, Joint Input-Output, and Two-Step Methods. 

In general terss, the purge-and-trap technique is the nethod of choice Cor detemining organic volatiles in water because of its ease of operation. If greater sensitivity is required, the closed loop stripping apparatus should be used. 

Analyze stability of a closed-loop system with three techniques ... 

The technique of using the damp ratio hne 0 = cos in Eq. (2-34) is apphed to higher order systems. When we do so, we are implicitly making the assumption that we have chosen the dominant closed-loop pole of a system and that this system can be approximated as a second order underdamped function at sufficiently large times. For this reason, root locus is also referred to as dominant pole design. 

Because carotenoids are light- and oxygen-sensitive, a closed-loop hyphenated technique such as the on-line coupling of high performance liquid chromatography (HPLC) together with nuclear magnetic resonance (NMR) spectroscopy can be used for the artifact-free structural determination of the different isomers. 

Grob and Zurcher [36,53-55] have carried out very detailed and systematic studies of the closed loop gas stripping procedure and applied it to the determination of parts per billion of 1-chloroalkanes in water. Westerdorf [56] applied the technique to chlorinated organics and aromatic and aliphatic hydrocarbons. 

Grob et al. [220-223] have carried out very detailed and systematic studies of the closed-loop gas stripping procedure and applied it to the determination of xg/l of 1-chloroalkanes in water. Westerdorf [224] applied the technique to chlorinated organics, and aromatic and aliphatic hydrocarbons. Waggot and Reid [225] reported that a factor of major concern in adapting the technique to more polluted samples is the capacity of the carbon filter, which usually contains only 1.5-2 mg carbon. They showed that the absolute capacity of such a filter for a homologous series of 1-chloro-n-alkanes was 6 xg for complete recovery. 

This brief overview of separate treatment techniques is not complete, however it can be used for a first inventory and identification of treatment steps which may be considered as part of a complete closed loop water system. It has to be taken in mind that the above-mentioned overview of separate treatment techniques is primarily based on one type of pollutant and one physical state of that pollutant. It will be clear that very often the same treatment step can be applied to remove different types of pollutants. It is also evident that a large percentage of the separate treatment steps mentioned will result in a concentrate containing the pollutants. This concentrate has to be treated subsequently. 

The controllability analysis was conducted in two parts. The theoretical control properties of the three schemes were first predicted through the use of the singular value decomposition (SVD) technique, and then closed-loop dynamic simulations were conducted to analyze the control behavior of each system and to compare those results with the theoretical predictions provided by SVD. 

In regard dynamics and control scopes, the contributions address analysis of open and closed-loop systems, fault detection and the dynamical behavior of controlled processes. Concerning control design, the contributors have exploited fuzzy and neuro-fuzzy techniques for control design and fault detection. Moreover, robust approaches to dynamical output feedback from geometric control are also included. In addition, the contributors have also enclosed results concerning the dynamics of controlled processes, such as the study of homoclinic orbits in controlled CSTR and the experimental evidence of how feedback interconnection in a recycling bioreactor can induce unpredictable (possibly chaotic) oscillations. 

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