Interpreting Process Control Diagrams

This comprehensive INVOLVE® interactive multimedia training program was produced in association with the Instrument Society of America. (ISA). This one lesson program trains participants how to interpret process and instrument diagrams.

Audience: This program is excellent for training instrument technicians and electricians as well as for the multi-craft training needs of process and manufacturing facilities.

Interpreting Process Control Diagrams

Prerequisites: This lesson is designed for participants familiar with instruments and control functions.

Description: This lesson introduces the common instrument and line symbols and notations used on process control and loop diagrams. The interpretation of process control and loop diagrams is presented as well. Emphasis is placed on identifying the functions of components within the process control system.


  • Identify the function, measured variable, location and accessibility, and loop identification of an instrument given its symbol and tag number
  • Identify the type of connection between an instrument and the process to which it’s connected when given a tag number
  • Identify signal line types (pneumatic, electrical, capillary, or internal software link)
  • Identify the type of valve actuator (diaphragm, motor, solenoid, or piston) when given a symbol
  • Describe the information available in a typical process control diagram, title block, revision list, materials list, and notes block
  • Describe the functional operation of the systems represented in typical process control diagrams
  • Understand the function of loop diagrams and their relationship to process control diagrams
  • Understand the purpose of each of the four areas of a typical loop diagram
  • Identify the location and type of each instrument port connection, junction box, and power source as well as the controller action for the instruments in a loop diagram
  • Describe the functional operation of the systems represented in a typical loop diagram