Level control operating principle

Transistor relays may also be used in coimection with contact manometers (< /. chap. 8.3.1 and 8.3.1.1). They are commercially available as a combination of standing or supported device. They operate on the normally open and normally closed principles where a circuit is switched on and off, respectively, on making a contact. These relays are further employed for photoelectric circuits, e.g. in the level control of liquids and in vacuum control (c/. chap, 8.6 and 8.3.1.1). As safety relays thev switch off the circuit if the contact thermometer fails. 

A variety of other configurations and modifications of the basic design shown in Figures 3-6 and 3zZ are possible. Valve trays (see Chapter lOi are popular. Downcomers can be chords of a circle as shown or circular pipes. Both partial and total condensers and a variety of reboilers are used. The column may have multiple feeds, sidestream withdrawals, intermediate reboilers or condensers, and so forth. The column also usually has a host of temperature, pressure, flow rate, and level measurement and control devices. Despite this variety, the operating principles are the same as for the sinple distillation column shown in Figure 3-6. 

Next, we assume that the primary control objective is to maintain plant operation as much as possible at the set points, despite fresh feed flow rate or composition changes. Thus, Fq (assuming it is not chosen as a manipulated variable) and zo are the disturbance variables. At this point in the analysis, a true plantwide control problem is encountered. Two control degrees of freedom remain, and either Fq or F could be manipulated to control reactor level. However, it is not obvious whether one choice or the other is better in some sense. In principle, the remaining flow rate (control degree of freedom) could be used to control z or B for example, if F is available, Fq is used as a manipulated variable for reactor-level control. 

Storage and receiving are activities that can greatly contribute to a safe and economic operation. It is here that quality control can be achieved at minimal cost. Label verification and other quality assurance measures can increase the confidence level that the correct chemicals have arrived, thereby potentially circumventing the use of wrong chemicals. Wrongly shipped chemicals can be returned to the manufacturer with minimal or no cost to the batch operation owner. As with all processes and activities it is of great importance to apply the principles of inherent safety, in particular the minimization and attenuation principles (CCPS G- 41). 

In this chapter we revisited an old problem, namely, exploring the information provided by a set of (x, y) operation data records and learn from it how to improve the behavior of the performance variable, y. Although some of the ideas and methodologies presented can be applied to other types of situations, we defined as our primary target an analysis at the supervisory control level of (x, y) data, generated by systems that cannot be described effectively through first-principles models, and whose performance depends to a large extent on quality-related issues and measurements. 

The Instrumentation and Control Fundamentals Handbook was developed to assist nuclear facility operating contractors provide operators, maintenance personnel, and the technical staff with the necessary fundamentals training to ensure a basic understanding of instrumentation and control systems. The handbook includes information on temperature, pressure, flow, and level detection systems position indication systems process control systems and radiation detection principles. This information will provide personnel with an understanding of the basic operation of various types of DOE nuclear facility instrumentation and control systems. 

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