Field-mounted instrument symbol
Also called Local instrument
A field-mounted instrument is installed in the plant at the process, read and maintained there.
What the field-mounted instrument symbol means
A field-mounted instrument is installed in the plant at the process, read and maintained there.
How it is drawn
A plain circle with the instrument tag inside: letters on top, loop number below.
The field-mounted instrument symbol in each standard
Drawn as ISA 5.1 defines it, as on most US and international legends.
ISO 10628-2 does not cover instruments. On ISO-based P&IDs they are drawn as IEC 62424 PCE requests, or to ISA 5.1 on many international projects.
German (DIN): PLT-Stelle vor Ort. See DIN P&ID symbols.
Where you see it on a P&ID
For gauges, local transmitters, switches and local controllers.
Tag codes
The field-mounted instrument is commonly tagged:
- PI
- TI
- PT
- LT
Tag formats follow the project numbering procedure. For instruments, the letters follow ISA 5.1, explained on the instrument symbols page.
Related symbols
Frequently asked questions
What does the field-mounted instrument symbol look like on a P&ID?
A plain circle with the instrument tag inside: letters on top, loop number below.
What is a field-mounted instrument used for?
A field-mounted instrument is installed in the plant at the process, read and maintained there. You will find it for gauges, local transmitters, switches and local controllers.
What tag does a field-mounted instrument have?
It is commonly tagged PI, TI, PT, LT. The exact tag format comes from the project numbering procedure and the legend sheets.
Is the field-mounted instrument symbol the same in ISA and ISO?
ISO 10628-2 does not cover instruments. On ISO-based P&IDs they are drawn as IEC 62424 PCE requests, or to ISA 5.1 on many international projects. Companies vary the details, so always check the legend sheets at the front of the P&ID set.
What is the field-mounted instrument called in German?
PLT-Stelle vor Ort. On a German R&I-Fließschema it is drawn to DIN EN ISO 10628-2 and DIN EN 62424.
- In production since 2014
- Thousands of daily users
- On MODEC FPSO projects since 2016