Side-by-side reference

Understand the difference.

Compare the meaning, drawing context and source references of two entries. A similar graphic or shared abbreviation does not establish equivalence.

First referenceCompare with

DO RELAY

Symbols

PLC relay output

A PLC relay output switches a documented contact path through the module's relay interface. The load supply and contact common may be separate from the PLC electronics supply.

Drawing use: Schematic
Application: Control circuits
Reference family: Manufacturer

A distinction that matters

A relay output is a contact interface, not a transistor output with the same supply/common behaviour.

Full reference

PLC I/O

Symbols

PLC input / output

A PLC input or output point connects a field signal with a controller module and channel. Input and output, digital and analogue, and one-wire or multi-wire arrangements are distinct characteristics. The module specification establishes electrical behaviour and terminal information.

Drawing use: Schematic
Application: Control circuits
Reference family: IEC / IEEE / ANSI

A distinction that matters

An input point, output point and communications connection are different interfaces. A generic box cannot establish their electrical compatibility.

Full reference

Original educational previews. Follow the source references on each full entry for the appropriate standard or selected product.