Industrial Engineer · phase 1 of 16 · noun

Local I/O

I/O installed in the same rack or local assembly as the controller.

The Explain card

Plain English
Local I/O sits in the same rack as the CPU, or bolted right beside it. It talks over the backplane rather than over a network.
Example
The pushbuttons and pilot lights on the main panel door land on cards in the controller's own rack.
Why it matters
Local points update every scan with no network delay and no cable to lose. They are also the points you cannot move without moving the controller, so the choice between local and remote is a layout choice as much as a wiring one.
Hook
If you can touch the CPU and the card at the same time, that is local.

Word knowledge

How the word is built, where it came from, and what it sits beside in memory.

In a sentence

On the ControlLogix chassis, Local I/O in slot 3 reads the door START pushbutton and slot 4 writes 24 V DC to the RUN lamp.

Why these words
  • local Latin localis, of a place, from locus, place supplies the place half, so the phrase is about nearness rather than about the signals
  • I/O English computing slash-pair of input and output, from in + put and out + put supplies the hardware half, naming the modules that take field signals in and send commands out
Where it came from
Origin
English industrial compound from Latin localis, of a place (from locus), and the computing slash pairing of input and output (in + put, out + put)
Entered the language
1980s
What changed
Local entered English from Late Latin localis, of a place, then named what sits with a processor rather than farther away. Input and output had meant putting in and taking out, then a 1950s slash joined them as I/O. PLC catalogs of the 1980s paired local with I/O once a second rack could sit on a remote scanner.
How it is spelled
Pattern
I/O is two capitals with a slash and no spaces, the same pattern as A/C and R/W
Pattern
Latin -alis becomes English -al, so local sits with vocal and legal
Breaks the pattern
I/O keeps the slash and both capitals even mid-sentence, never IO, I-O, or i/o
Breaks the pattern
mid-sentence the phrase is local I/O, with local uncapitalized; Local I/O is the drawing and title form
Breaks the pattern
the phrase stays two tokens; Local-I/O is a drawing error

Spelled like

  • A/C
  • R/W
  • vocal
  • legal
Broken into chunks
  • loc
    • location
    • locomotive
    • dislocate
  • al
    • vocal
    • legal
    • rural
  • I/O
    • A/C
    • R/W
    • I/P
  • put
    • input
    • output
    • throughput
What it sits beside

Same subject

Same shape

I/O family

Local versus remote pairs

Slash pairings

  • A/C
  • R/W
  • I/P

Where it sits in the deck

Phase 1: PLC Controller Hardware

The box itself, from processor and rack to the modules that plug into it, because nothing else in the deck lands until you know what a PLC physically is.

Neighbours in this phase