Process Flow Diagram use symbols and circles to represent each instrument and how they are connected in the process.
The International Society of Automation (www.isa.org) is a nonprofit professional association that sets the standard for those who apply engineering and technology to improve the management, safety, and cybersecurity of modern automation and control systems used across industry and critical infrastructure.
ISA5.1 is an industry standard used for Instrumentation Symbols and Identification. The compete documentation for advanced instrumentation users can be downloaded directly from their store for a nomainal fee. ANSI/ISA-5.1-2009, Instrumentation Symbols and Identification.
