DI, DO, AI & AO — Complete Guide for PLC, DCS & SCADA Engineers!

If you are learning industrial automation, understanding DI, DO, AI & AO is one of the most important fundamentals.

DI (Digital Input) → ON/OFF signals from field to PLC

DO (Digital Output) → PLC sends ON/OFF command to field devices

AI (Analog Input) → Continuous signals like 4-20 mA or 0-10 V

AO (Analog Output) → PLC controls devices proportionally

Common examples:

Push Button → DI

Motor Starter → DO

Pressure Transmitter → AI

Control Valve → AO

This infographic explains:

Difference between digital & analog signals

Real industrial examples

Signal flow in PLC systems

4-20 mA basics

Practical applications in industries

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