Industrial Engineer · phase 2 of 16
DI / Discrete Input
On or off input from a field device such as a switch, sensor, or pushbutton.
The Explain card
- Plain English
- A discrete input reads one thing that is either on or off. A switch is closed or open, a sensor sees the part or does not, and the card turns that into a single bit.
- Example
- The guard door switch feeds a discrete input. When the door opens the bit drops and the logic stops the machine.
- Why it matters
- Most of the decisions a machine makes come from these bits, so a wrong input type, a wrong voltage or a chattering contact corrupts everything downstream. Read the module's indicator light before you read the tag.
- Hook
- Yes or no, and the machine believes whichever one it sees.
Where it sits in the deck
Phase 2: PLC I/O and Field Signals
Where the controller meets the machine: discrete and analog signals, the wiring conventions behind them, and the field devices that send them.
