Field-mounted instrument.
A simple circle on a P&ID denoting a discrete instrument located in the field, accessible to the operator at the point of installation rather than mounted on a panel.
How it's drawn.
A plain circle with nothing crossing it. The tag sits inside. The measured-variable and function letters on the upper half, for example FT, PT, LIC, the loop number on the lower half. The empty circle is the message. A solid horizontal line through the middle moves the instrument to the primary panel. A dashed line puts it behind the panel. A square, hexagon, or diamond around it hands the function to a shared display or logic solver. A field-mounted instrument sits out at the process, reachable by the operator who walks the unit.
Variants.
- Single circle, no horizontal line. Field mounted
- Circle with solid horizontal line. Panel mounted, primary location accessible to the operator
- Circle with dashed horizontal line. Behind-panel mounting, not directly accessible
Typical usage.
Used for the bulk of process instruments installed near the equipment they measure. Flow transmitters on a pipe run, level transmitters on a vessel nozzle, pressure gauges next to a pump. The mounting line conventions encode whether the instrument is field-accessible, panel-accessible, or hidden in the back of a marshalling cabinet.
Telling it apart.
- No line through the circle is the test. The instant a horizontal line crosses it, the instrument is panel or control-room mounted, not in the field.
- A square, hexagon, or diamond around the bubble is not a mounting variant. It signals a shared display, computer function, or logic solver.
- The letters name the loop by function, not the hardware. FT is a flow transmitter however the flow is sensed.
Common questions
How do I know if an instrument is field or panel mounted from the symbol.
Related.
Get the P&ID symbol cheat sheet.
One page of mounting conventions, so field, panel, and behind-panel bubbles are told apart at a glance.