Types of Instrument Symbols ..

1. Instrument Symbols

Instrument symbols such as circles, lines, letters and numbers are use to provide information about the process.

Symbols may represent devices in the system or indicate how devices are connected to each other or to the process and also indicate its function. (i.e measure, indicate, record or control).

2. Line Symbols

Line symbols indicate how instruments are connected to each other and to the process and represents the types of signals transmitted in the process.

Line symbols could be either a process line symbol or a signal line symbol.
Note:
The single backlash signifying a discrete or binary signal type has been removed from the ISA standard as of 2009 ANSI publication. Regular pneumatic and electrical line symbols may represents either continuous or discrete states. The triple slash alternative line type for electrical symbols is also absent from the 2009 ANSI/ ISA standard.

3. Process line symbols

Process line symbols used to represent process lines and instrument connections. Process piping is generally shown with thick solid lines.

Thin solid lines indicate instrument to process connections or instrument tubing. In general, assume all instrument line is fine in relation to process piping line.

4. Valve and Actuators

Valves and Actuators that position them are critical parts of all process systems. Just as it is essential to know the meaning of the symbols for instruments, primary elements, lines and tag numbers when interpreting a process diagram, it is also necessary to recognize the symbols for actuators to interpret how these components function within the process.

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