Industrial Engineer · phase 2 of 16
DO / Discrete Output
On or off output used to command a relay, solenoid, starter, lamp, or other load.
The Explain card
- Plain English
- A discrete output is the controller saying on or off to the world. The card closes a contact or switches a transistor, and a relay, valve or lamp responds.
- Example
- The run bit for a conveyor lands on a discrete output that drives the coil of a motor starter. The starter carries the motor current, never the card.
- Why it matters
- Outputs are where a program bug becomes a physical event. Know each card's contact rating and what its channels do on a fault, because a stuck output can keep a valve open with nobody asking it to.
- Hook
- The bit that can actually hurt someone.
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.
