Controls and Instrumentation

Instruments are provided to monitor the key process variables during plant operation. They may be incorporated in automatic control loops, or used for the manual monitoring of the process operation. They may also be part of an automatic computer data logging system. Instruments monitoring critical process variables will be fitted with automatic alarms to alert the operators to critical and hazardous situations. 

Comprehensive reviews of process instruments and control equipment are published periodically in the journal Chemical Engineering. These reviews give details of all the instruments and control hardware available commercially, including those for the on-line analysis of stream compositions (Anon., 1969). Details of process instruments and control equipment can also be found in various handbooks, Perry et al. (1997) and Lipak (2003). 

It is desirable that the process variable to be monitored be measured directly often, however, this is impractical and some dependent variable, that is easier to measure, is monitored in its place. For example, in the control of distillation columns the continuous, on-line, analysis of the overhead product is desirable but difficult and expensive to achieve reliably, so temperature is often monitored as an indication of composition. The temperature instrument may form part of a control loop controlling, say, reflux flow with the composition of the overheads checked frequently by sampling and laboratory analysis. 

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More microprocessor-based process equipment, such as smart instruments and single-loop controllers, with digital communications capability are now becoming available and are used extensively in process plants. A fieldbus, which is a low-cost protocol, is necessary to perform efficient communication between the DCS and these devices. So-called mini-MAP architec ture was developed to satisfy process control and instrumentation requirements while incorporating existing ISA standards. It is intended to improve access time while... 

Figure 4-5. Typical control and instrument diagram for Process 1.

Control and instrumentation can be defined as subproducts for measuring, sending messages, controlling, and regulating. These are installed locally in each system, in the installation as a whole, or in the control technical room. 

TABLE 9.7 Important Information and Requirements for Control and Instrumentation... 

Plant equipment should have good access and controls and instruments should be clearly labeled. Under this category protective clothing and other equipment to enable safe operation is also included. 

The second slop is to obtain all the information about the process that will be needed for a Ihorongh evaluation including but not limited to the process materials used and their physical properties, the chemistry and tlicnnodynamics of the process, a plant layout, and a description of all the equipment used including controls and instrumentation. The last part of the information gathering step nitty be viewed as the preliminary formation of the What If questions. 

In-Kwon Yeo received the PhD degree in Statistics from University of Wisconsin-Madison in 1997. He joined the Department of Control and Instrumentation Engineering, Kangwon National University as a visiting professor in 2000 and the Division of Mathematics and Statistical Informatics, Chonbuk National University as an assistant professor in Korea. He is currently an associate professor at the Department of Statistics, Sookmyung Women s University. His current research interests include data transformations, multivariate time series analysis and generalized additive models. 

Garside, Robin, "Modular Zener Barrier Design Simplifies IS Installations", page 45, Control and Instrumentation, Vol II, No. 1, Jan 1979... 

Suggested control and instrumentation for the management of process components are shown in API RP I4C which is still relatively the standard within the industry. All process control systems are usually reviewed by a Process Hazard Analysis, which will deem if the provided mechanism area is adequate to prevent a catastrophic incident. 

Process controls and instrumentation only provide feedback for conditions within the process system. They do not report or control conditions outside the assumed process integrity limits. Fire and gas detection systems supplement process information systems with instrumentation that is located external to the process to warn of conditions that could be considered harmful if found outside the normal process environment. Fire and gas detection systems may be used to confirm the readings of major process releases or to report conditions that process instrumentation may not adequately report or be unable to report (i.e., minor process releases). 

Process control, valves and control panels should be easily accessible and viewable. ASTM standard F-l 166 provides graphical charts for the physical means to view and operable controls and instruments. 

See also Flocculants Flocculation analytical methods for, 11 640 applications of, 11 623-625 in automatic control and instrumentation systems, 11 639—640 chemical composition of, 11 625—639 economic aspects of, 11 642-644 health and safety factors related to,... 

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