Industrial Engineer · phase 7 of 16 · noun

Soft PLC

PLC runtime hosted on an industrial computer or virtualized platform instead of dedicated controller hardware.

The Explain card

Plain English
A soft PLC is the controller runtime running on an industrial PC or a virtual machine instead of on dedicated controller hardware. The logic is the same, the box is different.
Example
A CODESYS runtime on a fanless industrial PC controls a test stand. The same PC also runs the HMI and logs data to a database on the side.
Why it matters
It brings PC power and PC problems, since operating system updates, disk failures and shared CPU time all reach the control loop. Real time behaviour depends on how the runtime is isolated, and that has to be measured rather than assumed.
Hook
The controller is now an app.

Word knowledge

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

In a sentence

During commissioning, the engineer loaded the IEC 61131-3 project into the Soft PLC and verified the conveyor photoeye input.

Why these words
  • Soft Old English sōfte, gently or easily marks the software-oriented member of the controller class
  • PLC English initialism of programmable logic controller names the controller class being qualified
Where it came from
Origin
English compound formed from soft in its computing sense and the initialism PLC
Entered the language
1990s
What changed
Soft developed from describing physical yielding to contrasting software with fixed hardware, then became a modifier for controller implementations.
How it is spelled
Pattern
The modifier precedes the uppercase initialism PLC.
Pattern
PLC is written without periods between its letters.
Breaks the pattern
Generic usage often writes soft with a lowercase initial, while SoftPLC is also used as a closed compound and trademark.

Spelled like

  • safety PLC
  • compact PLC
  • virtual PLC
Broken into chunks
  • soft
    • software
    • soft starter
  • PLC
    • PLCs
    • micro-PLC
What it sits beside

Same subject

  • industrial PC
  • IEC 61131-3 runtime
  • distributed I/O
  • EtherCAT

Same shape

industrial controller types

Where it sits in the deck

Phase 7: PLC Related Automation Systems

The neighbours a PLC lives beside on a plant floor, from operator panels and SCADA up to the motion and batch systems it hands work to.

Neighbours in this phase