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A circle inside a diamond, marking logic functions.
Also known as: PLC symbol, Logic controller symbol
On a piping and instrumentation diagram a circle within a diamond denotes a function performed by a programmable logic controller, typically interlocks and sequences rather than continuous control.
Denotes a function implemented in programmable logic rather than in continuous control.
Contexts: Technical drawing
Separates interlock and sequence logic from continuous control on the drawing, which are usually different systems with different safety requirements.
Contexts: Technical drawing
A circle drawn inside a square standing on one corner, the two sharing a centre.