PLC function symbol
Also called Programmable logic controller
A PLC function is carried out in a programmable logic controller, often for sequences, interlocks and packages.
What the PLC function symbol means
A PLC function is carried out in a programmable logic controller, often for sequences, interlocks and packages.
How it is drawn
A diamond inside a square.
The PLC function symbol in each standard
Drawn as ISA 5.1 defines it, as on most US and international legends.
ISO 10628-2 does not cover instruments. On ISO-based P&IDs they are drawn as IEC 62424 PCE requests, or to ISA 5.1 on many international projects.
IEC 62424 has no separate symbol for this. Check the project legend.
German (DIN): SPS-Funktion. See DIN P&ID symbols.
Where you see it on a P&ID
For package control, sequences, burner management and interlocks.
Tag codes
The PLC function is commonly tagged:
- UY
- XY
Tag formats follow the project numbering procedure. For instruments, the letters follow ISA 5.1, explained on the instrument symbols page.
Related symbols
Frequently asked questions
What does the PLC function symbol look like on a P&ID?
A diamond inside a square.
What is a PLC function used for?
A PLC function is carried out in a programmable logic controller, often for sequences, interlocks and packages. You will find it for package control, sequences, burner management and interlocks.
What tag does a PLC function have?
It is commonly tagged UY, XY. The exact tag format comes from the project numbering procedure and the legend sheets.
Is the PLC function symbol the same in ISA and ISO?
ISO 10628-2 does not cover instruments. On ISO-based P&IDs they are drawn as IEC 62424 PCE requests, or to ISA 5.1 on many international projects. Companies vary the details, so always check the legend sheets at the front of the P&ID set.
What is the PLC function called in German?
SPS-Funktion. On a German R&I-Fließschema it is drawn to DIN EN ISO 10628-2 and DIN EN 62424.
- In production since 2014
- Thousands of daily users
- On MODEC FPSO projects since 2016