Ask about the difference between instrument circuit numbers and instrument tag numbers

Yes. The PI, TI, FT, PT, etc. above are circuit numbers, while 00001 below is the bit number.

Is PT also a circuit number? Is that supposed to be the instrument tag number?

Yes, in a PID diagram, the number indicated at the top is usually the instrument circuit number (also known as the circuit identifier), while the number indicated at the bottom is the instrument tag number (i.e., the installation location). The instrument circuit number is used to identify a specific circuit or signal path within the control system, whereas the instrument tag number indicates the exact installation location of the instrument in the plant. .

In the above diagram, PT also represents the circuit number; it shows a set of flow measurement instruments equipped with temperature and pressure compensation functions. This set of instruments consists of a flow measurement circuit (starting with the letter F), a temperature measurement circuit (starting with the letter T), and a pressure measurement circuit (starting with the letter P); each set of instruments has one tag number (00001). The diagram below also shows a pressure control system, whose tag number is 10401. PT is the pressure measurement transmitter circuit, PIC is the control and display circuit, PY is the converter circuit, and PV is the control valve; since it controls two valves, it is distinguished using the tag numbers 10401A and 10401B.

This post was last edited by leily1982 on 2025-1-3 14:14. The FIQ0001.TI0001, PI0001 mentioned above are circuit numbers; I stands for indication, and Q stands for accumulation. FT0001, TT0001, and PT0001 below are instrument tag numbers; T stands for transmitter. The original poster’s understanding is correct – don’t be misled by others.

I don’t seem to have understood quite well; let’s wait a bit longer

The loop tag is also known as the system tag; it is the tag of a system (control system, monitoring system, alarm system, etc.)； A system is composed of multiple instruments or units (including physical and virtual instruments), and the tag numbers of these instruments that make up the system are called instrument tags. For example, in Figure 1 for PI-00001, the various components that make up this system include the pressure transmitter PT-00001 (a physical instrument) and the pressure indicator PI-00001 (a virtual indicator). These two are instrument tags; PI-00001 serves as both an instrument tag and a system tag. For example, in Figure 2’s PIC-10401, the various components that make up this system include the pressure transmitter PT-10401 (a physical instrument), the pressure indication controller PIC-10401 (a virtual indication controller), PV-10401A and PY-10401A (electrical valve positioners for Valve A), and PV-10401B and PY-10401B (electrical valve positioners for Valve B). These are all instrument tag numbers; PIC-10401 is both an instrument tag number and a system tag number.

Thank you, very much. For example, things like PI and PIC are virtual; they can also be referred to as instrument tags or system tags

In other words, pressure, temperature, and flow each form a loop, okay

F is flow rate, T is temperature, P is pressure; the second letter T stands for transmission. FT, TT, or PT refer to transmitters – these are the actual instrument transmitters that send data to the DCS; they are given a name, which is known as a tag number. In DCS, you can display, record, and accumulate variables that are derived from the tag numbers rather than circuit numbers. In DCS, you create a series of variables to store these values or to display them; of course, you can establish these variables manually or have the system do it for you. FIQ0001 is the cumulative value of FT0001; the circuit number is more appropriately referred to as a derived variable (or tag).