What K means on a P&ID.
K shows up most often on drawings that pre-date the PLC era. Hardware timers and sequencers used to earn their own tag because they were physical relays you could point at. Modern PLC code does the same job invisibly. The K tags you still find on a 1985 drawing are usually batch-step sequencers or interlocking timers that have either been migrated to code already or are running on the original equipment for the next 20 years.
Also stands for.
- Time-rate of change
Common second letters.
| Tag | Meaning |
|---|---|
| KY | Computing element, KY. Timer or sequencer |
| KI | Indicator, KI. Time indicator |
Example tags.
| Tag | Meaning |
|---|---|
| KY-301 | Time-based computing element, often a sequencer step |
Typical placement.
On batch operations and sequence-driven processes. Most modern P&IDs do not carry K-prefix tags because timing logic lives in the PLC code rather than as a discrete drawn instrument.
Common questions
What does the ISA 5.1 first letter K stand for?
In ISA 5.1, the first letter K stands for Time, time schedule. It can also stand for Time-rate of change.
How is letter K typically used on a P&ID?
On batch operations and sequence-driven processes. Most modern P&IDs do not carry K-prefix tags because timing logic lives in the PLC code rather than as a discrete drawn instrument.
What second letters commonly follow K in ISA 5.1 tags?
Common combinations include KY (Computing element, KY. Timer or sequencer), KI (Indicator, KI. Time indicator).
What are example ISA 5.1 tags starting with K?
KY-301 (Time-based computing element, often a sequencer step).
Run it on your drawings.
Upload a P&ID set and see every tag read in the convention the drawing already uses.