Industrial Engineer · phase 6 of 16

PL

Performance Level, a safety-related control-system capability rating under ISO 13849-1.

The Explain card

Plain English: Performance Level is the machinery world's rating for a safety control function, from PL a up to PL e. It comes from ISO 13849 and folds together architecture, reliability, diagnostics and resistance to common cause failure.
Example: A guard door on a press is assessed as needing PL d. Dual channel switches, a safety relay or safety PLC with monitoring, and monitored contactors are how the circuit gets there.
Why it matters: PL is the rating a machine builder is asked for in Europe and increasingly everywhere, and it maps roughly onto SIL for the same risk. The category of the architecture is only one input, so a category 3 circuit is not automatically a PL d one.
Hook: The grade a machine's safety circuit gets.

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

In a sentence

During validation, the engineer confirms that the dual-channel guard-door circuit achieves PL d before the conveyor is commissioned.

Letter by letter

Where it came from

Origin: English initialism coined from Performance Level in ISO 13849-1 terminology
Entered the language: 2006
What changed: Standardized with lowercase grades a through e, then adopted as routine machinery-safety shorthand.

How it is spelled

Capitalisation: Always uppercase PL, including mid-sentence; a following grade letter is lowercase, as in PL d.
Plural and possessive: The plural is PLs, the singular possessive is PL's, and the plural possessive is PLs'.
Out loud: Spelled out letter by letter.

Same family

Broken into chunks

What it sits beside

Same subject

Same shape

ISO 13849 grade notation

Functional-safety rating abbreviations

Phase 6: PLC Operating Modes, Safety, and Diagnostics

Run, program and fault: what a controller does when something goes wrong, and the safety functions that decide how much that costs.