Performance feedback mechanism

The AVR may be designed for variable duty, for automatic control of the reactive power, to the required level through feedback control systems. The machines will now operate only as synchronous condensers without performing any mechanical duty. 

Crystallization from solution is a widely utilized separation and purification technique in chemical industry. It is characterized by the formation of a spectrum of differently sized crystals. This spectrum, called the Crystal Size Distribution or CSD, is highly important for the performance of the crystallizer, the crystal handling equipment like centrifuges and dryers, and the marketability of the produced crystals. However, in many industrial crystallizers, the observed CSD s show large transients due to disturbances or are unstable because of the internal feedback mechanisms of the crystallization process ). The main limitation for effective CSD control was the lack of a good on-line CSD measurement device, but recent developments show that this hurdle is taken (2). 

Note that the expression for Rlpp itself depends on the dynamic structure factor. Thus the calculation of F(q, t) and Rlpf) should be performed self-consistently. We shall discuss in the next section that this self-consistency provides a feedback mechanism and leads to a divergence of the dynamic structure factor at zero frequency. 

Photoswitchable enzymes could have an important role in controlling biochemical transformations in bioreactors. Various biotechnological processes generate an inhibitor, or alter the environmental conditions (pH, for example) of the reaction medium. Photochemical activation of enzymes that adjust environmental conditions or deplete the inhibitor to a low concentration may maintain the bioreactor at optimal performance. More specifically, integration of the photoswitchable biocataly-tic matrix with a sensory electrode might yield a feedback mechanism in which the sensor element triggers the light-induced activation/deactivation of the photosensitive biocatalyst. 

This second-level modeling of the feedback mechanisms leads to nonlinear models for processes, which, under some experimental conditions, may exhibit chaotic behavior. The previous equation is termed bilinear because of the presence of the b [y (/,)] r (I,) term and it is the general formalism for models in biology, ecology, industrial applications, and socioeconomic processes [601]. Bilinear mathematical models are useful to real-world dynamic behavior because of their variable structure. It has been shown that processes described by bilinear models are generally more controllable and offer better performance in control than linear systems. We emphasize that the unstable inherent character of chaotic systems fits exactly within the complete controllability principle discussed for bilinear mathematical models [601] additive control may be used to steer the system to new equilibrium points, and multiplicative control, either to stabilize a chaotic behavior or to enlarge the attainable space. Then, bilinear systems are of extreme importance in the design and use of optimal control for chaotic behaviors. We can now understand the butterfly effect, i.e., the extreme sensitivity of chaotic systems to tiny perturbations described in Chapter 3. 

The Schirmer II test can be performed in extremely dry eyes with very low results on Schirmer I. Before removing the paper strips at the conclusion of the Schirmer I test, a cotton swab is inserted into the nose to mechanically irritate the nasal mucosa. In normal subjects this stimulates an impressive basal tear secretion. If this response is present, ocular surface disease that has interfered with the normal neurologic feedback mechanism is suspected of contributing to the dry eye state. If the response is absent, lacrimal gland dysfunction is the likely cause. 

A control plan is the sum of the procedures and equipment used to ensure that the internal requirements are met. It includes control charts, sampling plans, 100% inspection, feed-forward/feedback mechanisms, and mistake-proofing tech-niques/devices. Some items may be performed by equipment like automatic controllers, and some are performed by operators and checkers. There may not be a single document called a control plan. Instead, these controls might be spread across a number of documents including a statistical process control plan, an inspection plan, an operator manual, and various other standard operating procedure and specifications. 

An important attribute of flow analysis started with the advent of computer facilities in the laboratory. Discretely operated devices in the manifold were exploited in advanced multi-commuted flow systems. These devices initially supported the main injector by performing specific tasks [105], especially those requiring external timing control and/or concentration-oriented feedback mechanisms. The concept became more established after a landmark article on multi-commutation [106],... 

Flow ratiometry. Flow rates of the convergent sample and titrant streams are varied in real time according to a concentration-oriented feedback mechanism and the ratio of flow rates associated with the end point is used to estimate the analytical result. Flow rate variations are performed using, e.g., stream directing valves or computer-controlled fluid delivery devices [332,333]. 

Management of the sample and titrant plugs. The number and length of the plugs of the solutions involved (carrier, wash, titrant and titrand) can be easily modified, allowing the development of true flow titrations [336,337], These modifications can be performed in real time in accordance with a concentration-oriented feedback mechanism and this is the essence of expert titration flow systems. 

Another possibility is to take advantage of the individual treatment of every assayed sample. For sample lots with high variability in, e.g., pH or ionic strength, the required adjustments can be made in accordance with a prior assay performed in-line. This approach was proposed for the spectrophotometric determination of total nitrogen in Kjeldahl digests of plant leaves [397], As the method was very susceptible to sample acidity, which varied from sample to sample, individual sample pH adjustment was needed. To this end, an alkaline solution was added to every sample and the amount added was determined according to a pH-orientated feedback mechanism. This innovation was further applied to the spectrophotometric determination of aluminium in plant digests [398] and iron in estuarine waters [399], characterised by pronounced variations in... 

Automatic and automated instruments can be differentiated as follows automatic instruments tend to perform specific operations at given points in a process or analysis to save time or effort, e.g. robotics, while automated instruments tend to control some part of a process without human intervention and do this by means of a feedback mechanism from sensors. For example, an automatic conductivity detector might continuously monitor the conductivity of a process stream, generating some alarm if the conductivity goes outside a preset limit. An automated detection system could transmit the measured conductivity values to a control unit that, by utilising a feedback mechanism, adjusts relevant process parameters, e.g. temperature or cycle time, to maintain the conductivity of the stream within the preset limits. 

To understand the dynamic aspects of accidents, the process leading to the loss can be viewed as an adaptive feedback function where the safety control system performance degrades over time as the system attempts to meet a complex set of goals and values. Adaptation is critical in understanding accidents, and the adaptive feedback mechanism inherent in the model allows a STAMP analysis to incorporate adaptation as a fundamental system property. 

The primary objective of measuring safety performance is to provide a feedback mechanism that will foster continuous improvement. A process for implementing such a program relies on the following steps (Krause and Hidley 1990,161) ... 

The primary objective of measuring safety performance is to provide a feedback mechanism that will foster continuous improvement... 

Constituting a first filter for suppliers within the oil industry, FPA is an industry-wide initiative that has established standard performance criteria. Not only has it decreased search costs, but has also encouraged competition and self-auditing amongst suppliers, providing a feedback mechanism that highlights their faults. 

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