【Y2025】Common problems in the assignment of instrument tag numbers and methods for their assignment
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This post was last edited by zhoudingshengs on 2025-2-6 08:34. The attachment contains: the common problems in the assignment of instrument tag numbers and the methods for assigning them.
In detection and control systems, each instrument (or component) that makes up a loop should have its own unique instrument tag number.
The method of representing instrument tags and their use in instrument system diagrams can be explained by referring to the standard HG/T 20505-2014 on functional indicators and graphic symbols for process measurement and control instruments.
Instrument tag numbers are classified according to the measured variable; that is, for the same measured variable in the same device (or section), the numerical identifiers of the instrument tag numbers are sequential. But empty numbers in between are allowed ； The instrument tag numbers of variables that are not visible cannot be numbered sequentially.
If there are two or more instruments with the same function in the same instrument circuit, suffixes (uppercase letters) can be added after the instrument tag to distinguish them; for example, PT-202A and PT-202B represent two transmitters in the same circuit； PV-201A and PV-201B refer to two control valves in the same circuit.
When multiple sensing elements belonging to different sections share one display instrument, the instrument tag is assigned only a sequential number without indicating the section number; for example, the instrument tag for a multi-point temperature monitoring device is TI-1, while the instrument tags for the corresponding sensing elements are TE-1-1, TE-1-2, and so on.
When an instrument is shared by two or more circuits, the instrument tag numbers for each circuit should be indicated. For example, when a two-channel paperless recorder is used to measure flow and pressure, the instrument tag numbers will be FR-121/PR-131; if it is used to measure the flow in two circuits, the tag numbers will be FR-101/FR-102 or FR101/102.
The notation method for instrument tags on control point flowcharts and instrument system diagrams is as follows: the letter code is placed in the upper half of the circle, while the circuit number is placed in the lower half of the circle.