Free AutoCAD instrumentation symbols (DWG), ISA 5.1 style

About ISA 5.1

ISA 5.1 (ANSI/ISA-5.1-2009) is the standard for instrumentation symbols and identification on P&IDs and loop diagrams. In its bubble table a circle is a discrete instrument, a circle in a square is shared display and shared control (the primary choice, the basic process control system such as a DCS or a PLC), a diamond in a square is the alternate choice or a safety instrumented system, and a hexagon is a computer system or software function.

These symbols are our own drawings after the symbol tables of the standard. They are not copied from it, because it is a paid publication, and the library is not certified against it. Company and project standards often differ in details such as the bubble size and the number of location lines; change the blocks if yours do.

Frequently asked questions

Are these symbols ISA 5.1 compliant?

They are drawn after the common ISA 5.1 forms, not checked clause by clause and not certified. The standard is a paid publication that we have not copied. If a client requires strict conformance, compare the shapes with your copy of the standard.

How do I show that a function runs in the DCS or in the PLC?

Use the shared display and shared control bubble (a circle inside a square) for a function in the basic process control system, whether that is a DCS or a PLC, a hexagon for a function in computer software and a diamond inside a square for the safety instrumented system. The line across the bubble shows where it is mounted or displayed. PLC I/O modules have no standard drawing: every manufacturer has its own module pictures, so they are not part of this library.

Does the library contain every symbol of ISA 5.1?

No. It covers the main symbol tables: bubbles, primary elements, secondary instruments, accessories, connections, signal lines, valve bodies, actuators, regulators, safety devices and control valves. Some combined assemblies (for example regulators drawn with vessels or bubbles) and the binary logic and function symbols are not included.

Can I use the symbols in commercial projects?

Yes. They are free to use and modify in your own projects, including commercial ones. They are provided as is, without warranty.

Can I change the bubble size or add attributes?

Yes. Open the DWG, edit a block with BEDIT to change it or add attributes, and save. To update drawings that already contain the block, run ATTSYNC or replace the block. Make a backup first: attribute values can be lost if ATTSYNC is used carelessly.

Where do I find a ready-made set of these symbols for AutoCAD?

AutoCAD itself ships only a small set of sample blocks, so a full symbol set has to come from a library. Download the ZIP on this page and open the DWG: every symbol is a block. Insert one with INSERT (Blocks palette, Libraries tab, then pick the DWG) or drag it from DesignCenter (ADCENTER). You can also download a single symbol on its own.