Symbols, process instruments

Instrumentation normally is denoted by a circle in which the variable being measured or controlled is denoted by an appropriate letter symbol inside the circle. When the control device is to be located remotely, the circle is divided in half with a horizontal line. Table 1.3 gives various instrumentation symbols and corresponding letter codes. The specific operating details and selection criteria for various process instrumentation are not discussed in this book. The reader is referred to earlier works by Cheremisinoff [1,2] for discussions on essential control and measurement instrumentation. 

Figure 1-20B. Commonly used instruments for process instrumentation flowsheets. Adapted by permission, ISA Std. ANSI Y32.20—1975, ISA S5.1—1973, Instrumentation Symbols and Identification," Latest edition, 1984.

In general, it appears that expert systems which combine symbolic/numeric processing capabilities are necessary to effectively automate decision-making in applications involving analytical and process instrumentation/sensors. Furthermore, these integrated decision structures will likely be embedded (67-69) within the analytical or process units to provide fully automated pattern recognition/correlation systems for future intelligent instrumentation. 

Figure 3.4. Symbols for control elements to be used on flowsheets. Instrument Society of America (ISA) publication no. S51.5 is devoted to process instrumentation terminology.

Data on spare and parallel equipment are often omitted. Valving is also generally omitted. A alve is shown only where its specification can aid in understanding intermittent or alternate flows. Instrumentation is indicated to show the location of variables being controlled and the location of the actuating device, usually a control valve. To help the reader better understand the process flow sheet, a list of commonly used symbols is presented in Fig. 5.9.1. 

The symbols used to show the equipment, valves, instruments and control loops will depend on the practice of the particular design office. The equipment symbols are usually more detailed than those used for the process flow-sheet. A typical example of a P and I diagram is shown in Figure 5.25. 

An important aspect of our AI application is the attention paid to including well-established Fortran programs and database search methods into the decision structure of an expert system network. Only certain AI software tools (such as TIMM) effectively handle this critical aspect for the analytical instrumentation field at this time (57-60)> The ability to combine symbolic and numeric processing appears to be a major factor in development of multilevel expert systems for practical instrumentation use. Therefore, the expert systems in the EXMAT linked network access factor values and the decisions from EXMATH, an expert system with chemometric/Fortran routines which are appropriate to the nature of the instrumental data and the information needed by the analyst. Pattern recognition and correlation methods are basic capabilities in this field. 

BS 1646 1979 British Standard 1646 (British Standards Institution, London) Symbolic representation for process measurement control functions and instrumentation. 

BS 1646 1984 Symbolic representation for process measurement control functions and instrumentation. 

Many chemical and petroleum companies are now using Process Industry Practices (PIP) criteria for the development of P IDs. These criteria include symbols and nomenclature for typical equipment, instrumentation, and piping. They are compatible with industry codes of the American National Standards Institute (ANSI), American Society of Mechanical Engineers (ASME), Instrument Society of America (ISA), and Tubular Exchanger Manufacturers Association (TEMA). The PIP criteria can be applied irrespective of whatever Computer Assisted Design (CAD) system is used to develop P IDs. Process Industries Practice (1998) may be obtained from the Construction Industry Institute mentioned in the References. 

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