What is I/O (Input/Output)?
I/O, or Input/Output, refers to all signals or data a system receives (input) or sends (output) to the outside world. In industrial automation, it concerns physical or digital connections between a control system (such as a PLC) and the process equipment, such as Sensors and Actuators.
I/O is the bridge between software/logic and the physical world.
🔌 Types of I/O in industrial automation
| Type | Description | Examples |
|---|---|---|
| Digital input (DI) | Receives binary signals (on/off) | Push button, limit switch, emergency stop |
| Digital output (DO) | Sends binary signals | Driving lamps, valves, relays |
| Analogue input (AI) | Receives variable signals (e.g. 4–20 mA or 0–10 V) | Temperature sensor, pressure transmitter |
| Analogue output (AO) | Sends variable signals | Control valve, variable frequency drive, PID control |
| Virtual or software I/O | Internal signals within a SCADA or PLC program | Software alarms, logic outputs |
📦 Centralised vs. distributed I/O
| Centralised I/O | Distributed I/O |
|---|---|
| In one cabinet close to the PLC | I/O modules spread across the field, linked via a network |
| Shorter cable runs, simple wiring | More flexible, scalable, less physical cabling |
| Common in classic PLC installations | Used in large installations or SCADA networks |
Examples of I/O networks: ProfiNET, EtherCAT, Modbus TCP, IO-Link
🧠 Why is I/O important?
- Connects the physical world (sensors, motors) with digital logic
- Determines which processes you can measure and control
- Is crucial for safe, reliable and flexible automation
- Plays a central role in SCADA, DCS, MES and PLC systems
📌 In summary
I/O (Input/Output) forms the basis of automation by handling signals to and from the real world. Without I/O there is no control, Monitoring or automation in a production or process environment.