PLC / alternate control system function
ISA 5.1-2009/2022 (general instrument and function symbols)
Drawn as
A diamond inside a square, with a horizontal line across when operator-accessible.
Meaning
A function in a PLC or other non-BPCS control system: package PLCs, sequence logic, compressor UCP. Software, not modelled.
Variants
- ISA 5.1-2009 lets the user assign diamond-in-square to either "alternate control system" or SIS; the drawing legend says which
- Some old sources describe a triangle-in-square for PLCs; the standard shape is the diamond
Tags
YIC · XC · HS
Not physical hardware. Read it, then skip it in the 3D model.