What do the lines through an instrument bubble mean (field vs DCS vs PLC)?

Question

Some instrument bubbles on our drawings are plain circles, some have a horizontal line through them, some are a circle inside a square, and one type is a square with a diamond inside. I know they mean something about where the device lives but I can never remember which is which.

Can someone lay out the shape and line conventions clearly?

Can someone lay out the shape and line conventions clearly?

Pau · Accepted Answer

Two separate things are encoded: the OUTER SHAPE tells you the device type, and the LINE THROUGH the bubble tells you the location/accessibility.

Shapes: a plain circle is a discrete, individually-mounted instrument. A circle inscribed in a square is shared display / shared control — i.e. a DCS or SCADA function. A hexagon is a computer/advanced-control function. A square with an inscribed diamond is a PLC (programmable logic control) function.

Lines: no line = field mounted, out at the process. A single solid horizontal line = mounted in a primary/normally-accessible location, typically the front of the main control-room panel. A single dashed line = located behind the panel, not normally accessible to the operator. A double solid line = a secondary or local panel (auxiliary location).

So a circle-in-square with a solid line is a DCS point the operator sees at the main console; a plain circle with no line is a field transmitter; a diamond-in-square with no line is a PLC I/O point acting in the field. Combine the two axes and any bubble is unambiguous. Full set with drawings: /learn/instrument-symbols.html and /standards/isa-5-1.html

What do the lines through an instrument bubble mean (field vs DCS vs PLC)?

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