How to read a tag
In ISA-style identification the first letter is usually the measured variable (P pressure, F flow, L level, T temperature). The following letters describe the function: I indicate, T transmit, C control, S switch, with H or L for high or low.
The number after the letters, such as 101 in PT-101, is the loop number. Every instrument in the same control loop normally shares it.
Common examples
- PT — Pressure transmitter
- PI — Pressure indicator
- PIT — Pressure indicating transmitter
- PIC — Pressure indicating controller
- PSH — Pressure switch high
- FT — Flow transmitter
- LT — Level transmitter
- TT — Temperature transmitter
Your project's instrument index and drawing specification decide the exact letters. This list is a starting point, not the full ISA table.
Field instrument bubble
PT-101
Where the bubble sits also matters: see field vs control room instruments.
Try an instrument in InduDraft
Open a P&ID with ISA selected and type your own tag letters.
Start ISA P&ID