Instrumentation symbols

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 5.9.2b. Typical instrumentation symbols for pressure. Transportation...

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.

The instrument symbols of Table 1-4 and Figures 1-23B and C are representative of the types developed by the Instrument Society of America and some companies. 

Table 5.1. Letter Code for Instrument Symbols (Based on BS 1646 1979)...

Instrument Symbols and Identification, ISA-S5. Instrument Society of America, Pittsburgh, 1973. 

Rather less freedom is allowed in the construction of mechanical flowsheets. The relative elevations and sizes of equipment are preserved as much as possible, but all pumps usually arc shown at the same level near the bottom of the drawing. Tabulations of instrumentation symbols or of control valve sizes or of relief valve sizes also often appear on P I diagrams. Engineering offices have elaborate checklists of information that should be included on the flowsheet, but such information is beyond the scope here. 

This example illustrates how the techniques used in an operability study can be used to decide the instrumentation required for safe operation. Figure 9.6a shows the basic instrumentation and control systems required for the steady-state operation of the reactor section of the nitric acid process introduced in Figure 4.2. Figure 9.6b shows the additional instrumentation and safety trips added after making the operability study set out in this section. The instrument symbols used are explained in Chapter 5. 

The hot section (Fig. 5) is controlled by a cascade loop which is based on a selected pumping rate (150 gpm) and sterilization temperature set in the TIC. Changes in the feed temperature are monitored at TTl which will automatically override the steam supply to keep the temperature at set point. Steam flow rate is monitored (by FE) and flow is automatically compensated should a large drawdown of steam occur elsewhere in the plant. Temperature is recorded at the beginning and end of the hot section. The hot section should be well insulated and special care should be given to the pipe supports for expansion. (Instrumentation symbols used here and in Figs. 3, 5, 6 and 7, conform to the standard symbols of the Instrument Society of America.)... 

Symbols for instrumentation are usually based on the standard reference Basic Instrumentation Symbols RP5 developed by ISA. Instrumentation symbols fall into three categories temperature, pressure, and flow indicators. 

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