Instrument Tag Builder (ISA 5.1)
Build a correct instrument tag from its parts: first letter for the measured variable, an optional modifier, the function letters, an alarm or switch limit and the loop number.
Tag Structure (ISA 5.1)
Example: P + D + I + T + 101 = PDIT 101
The first letter is the measured or initiating variable. Modifiers such as D (differential) follow it directly. Succeeding letters give the function (indicate, transmit, control, alarm, switch, valve). H and L limits follow alarms and switches.
Worked example
Level, switch, high high, loop 205: LSHH 205, a level switch high high. Flow, indicate and control, loop 101: FIC 101.
Frequently Asked Questions
Why is a level control valve called LV?
Tags follow the loop variable; the valve in a level loop is LV.
What is the difference between PT and PIT?
PIT is a transmitter with a local indicator; many projects use PT for both.
Where do H and L go?
After the function letter, as in PAH (pressure alarm high) or LSL (level switch low).
Learn more on the blog
Instrument index: 10 essential columns
A practical, field focused guide on instrumentationblog.in that explains the theory behind this tool and how engineers apply it on real plants.
Read Full Article