Control room instrument

How to read it

A line across the bubble moves the instrument indoors. The DOE’s handbook calls this a board-mounted instrument and draws an instrument behind the board with a dashed line instead. Kuphaldt’s Lessons In Industrial Instrumentation sets out the ISA bubbles: a solid line for the front of the main control room panel, a dashed line for the rear of it, and two lines for an auxiliary panel elsewhere, front or rear in the same way.

The course text by Jonathan Verret and others explains front and back: the front panel faced the operators with the manual controls and displays, and the back held instruments that are less important or looked at less often. It notes that panels have largely been replaced by screens the operators switch between, and in one exercise reads a tagged bubble as a flow indicator and controller on the front panel, with an electrical connection.

Also searched as: board mounted instrument symbol, control room instrument p&id symbol, control room instrument symbol, panel mounted instrument symbol.

How to read the tag letters

The letters in a bubble are the instrument’s tag, and the number under them is its loop. In Kuphaldt’s account of the ISA 5.1 system, the first letter is the variable the loop measures or controls, whatever the device itself senses: every instrument in a level loop starts with L, even a transmitter that infers level from pressure. The letters after it are the functions. So FIC is a flow indicating controller, PT a pressure transmitter, TE a temperature element and LT a level transmitter, and FC-135 is a flow controller in loop 135. The DOE’s handbook builds tags the same way, from the sensed parameter, then the indicator or controller type, then the type of component.

Look-alikes

A plain circle is a field-mounted instrument. The same circle inside a square is a shared display.