Y - Event, state, presence
Reference for the ISA 5.1 first letter Y. First-letter Y is rare in modern drawings. State and event detection migrated to Z-prefix position switches and service-letter switches, FS, PS, LS decades ago. The Y tags you do see are usually relics on legacy drawings that haven't been redrafted since the 1980s. Second-letter Y, by contrast, is everywhere as the computing-relay marker, FY, PY, TY.
Read one of your own drawings.
Drop a P&ID, instrument index, or schedule. Tagsight reads it to the tag and opens a workspace you keep when you sign in.
PDF · DWG · DXF · TIFF · PNG · XLSX
Also stands for.
- Modifier. Computing relay, when used as a second letter, e.g. FY, PY
Common second letters.
Switch, YS. State switch
Alarm high, YAH. State alarm
Example tags.
State switch, often a presence detector or event indicator
Typical placement.
On event detection scope. Flame failure detectors, often combined with B-prefix, end-of-stroke switches on actuators, often combined with Z-prefix. First-letter Y is rare. Second-letter Y, computing relay is much more common.