What Changed in ISA 5.1-2022 for I/O Lists.

ISA 5.1 was last revised before most engineers reading this finished school. The 2022 revision refines a few things that the 2009 version had to talk around, mostly because digital and networked devices were the exception then and are the rule now.

If you maintain a house standard that references ISA 5.1, this is the cycle to consider migrating to the 2022 edition.

Summary of changes. 2009 vs 2022

The table below lists the main areas where the two editions differ. The tag identification rules in the left column are stable. Everything in the right column changed at least in part.

What was added or refined

Digital and shared-display devices

The 2009 standard distinguished panel-mounted and field-mounted instruments by drawing a horizontal line through the circle. Digital DCS, PLC functions, the controller logic itself, not the field instrument were typically drawn as a hexagon. The 2022 revision keeps the hexagon and adds clearer conventions for shared-display instruments where the same physical signal reads on multiple HMI graphics.

Before, 2009. A DCS temperature controller might appear as a TIC inside a dashed-line circle, with no further annotation to indicate it appears on three separate HMI graphics. Engineers reading the drawing had to know from context whether the dashed-line circle was a field instrument with a shared display or a pure software block.

After, 2022. Shared-display instruments carry an explicit annotation to distinguish multi-graphic display from the single-graphic DCS function. A TIC that appears on both a unit overview and a detailed loop graphic is annotated to reflect that. This reduces ambiguity when extracting the I/O list. A shared-display software block does not generate a wired I/O point, regardless of how many graphics it appears on.

Function block annotations

Computing relays, FY, PY, TY now have refined annotation rules for the math the block performs. The pre-2022 convention put the math symbol inside the circle. The 2022 convention puts a brief annotation alongside, which is more legible for non-trivial computing blocks.

**Before, 2009 example. ** A flow ratio computing block appeared as a small division symbol inside the FY circle. On a complex P&ID at reduced print scale, this was nearly unreadable.

**After, 2022 example. ** The FY circle carries the annotation "RATIO" or the relevant engineering formula alongside the symbol, outside the circle. A summing block is labeled "SUM" rather than carrying an ambiguous sigma character inside a 12mm circle.

The symbol shape, hexagon or circle with annotation is unchanged.

Network-attached devices

The 2022 revision adds explicit conventions for instruments on a digital bus, Foundation Fieldbus, PROFIBUS-PA where the physical wiring is shared and the I/O channel allocation is logical rather than physical.

Before, 2022. A set of HART or Foundation Fieldbus devices was shown with individual instrument circles, often with a note block stating "FF segment 3" or similar. There was no standardised way to show the bus segment on the drawing.

After, 2022. A dedicated bus-segment line connects the devices, with the protocol annotated on the segment. Individual instruments on the bus carry a bus-tag annotation. This makes it clearer when counting I/O that these devices share one fieldbus card port, not one analog card channel each.

From an I/O list perspective. A Foundation Fieldbus transmitter is still one instrument row. The card type column changes from AI (4-20mA) to FF H1, and the card-count calculation changes from one-device-per-channel to segment-based counting, typically 12-16 devices per card port. The 2022 drawing convention surfaces this distinction more clearly.

Valve actuator detail

The 2009 standard used a standard triangle symbol for all valve actuators. Actuator type, pneumatic, electric, hydraulic was recorded in the instrument data sheet or the valve specification, not the P&ID.

The 2022 revision introduces explicit actuator-type annotation on the valve symbol. A pneumatic diaphragm actuator now carries a specific indicator. An electric actuator carries another. This matters when the P&ID is the primary source for building a valve list. With 2022 drawings you can derive actuator type directly from the drawing. With 2009 drawings you need the instrument data sheets.

Panel-mounting clarifications

The horizontal-line conventions for primary panel, secondary panel, and behind-panel mounting are clarified, particularly for the dashed-line behind-panel case.

Before, 2009. A dashed horizontal line through an instrument circle indicated a device mounted behind the panel. On complex P&IDs with many field-mounted DCS instruments also using dashed lines for shared-display, these two meanings were easily confused.

After, 2022. The behind-panel convention is explicitly distinguished from the shared-display convention, with clear examples in the standard's figures. Panel versus shared-display no longer share the same line style.

Ratio and multivariable letter codes

ISA 5.1-2009 left ratio and multivariable functions to user's choice letters. In practice, engineers used FFY for flow ratio, two flow variables being ratioed and UTT for a multivariable transmitter measuring temperature and pressure simultaneously. The conventions were informal.

ISA 5.1-2022 adds explicit guidance. The double-F prefix, FF is formally recognised for flow ratio loops. The U first letter is confirmed for multifunction, multivariable transmitters. These are not new tag types. They are formalisation of what most experienced engineers were already doing. The practical effect is that the letter reference table in the standard now includes these entries, which reduces per-project debate about the "correct" notation.

Analyzer line notation

Analyzer systems, chromatographs, gas quality analysers, online spectrometers require sample conditioning equipment. Sample probes, filter coalescers, sample coolers, transport tubing, and the analyser house itself. ISA 5.1-2009 did not define a specific line style for sample conditioning streams. Engineering companies drew these however they chose.

ISA 5.1-2022 adds a dedicated line style for sample transport lines, distinguishing them from process piping and from instrument signal lines. When reading a 2022 analyser P&ID, the sample conditioning system is now clearly delimited from the process P&ID and from the instrument loop diagram.

For the I/O list this matters in a specific way. The analyser transmitter, AIT is still one AI point. But the sample system may include solenoid valves, SOV, DO, pressure switches, PSL, DI, and heaters, controlled via TIC, AO. These are now more consistently visible on the drawing because the sample-line convention draws the system boundary explicitly.

What did not change

Tag identification. First letter, second letter, modifier letters, loop number. The rules that govern FT-101 still govern FT-101. If you can read a 2009 drawing, you can read a 2022 drawing.

Standard symbology for analog instruments. Circles, lines, valves, vessels. The core symbols a P&ID uses for the majority of its content. Unchanged.

Loop-numbering schemes. Operating-company-specific conventions, area-loop-suffix, train-loop-redundancy layer on top of ISA 5.1 and are not addressed in the standard. The 2022 revision does not change that boundary.

Signal classification for AI, AO, DI, DO. The first-letter and modifier-letter rules that drive signal class assignment are stable. See ISA 5.1 letter codes for the full reference.

When to update your house standard

Three triggers that justify an update cycle.

You are starting a greenfield project. New drawings should use the most current edition the project's regulatory environment accepts. If your owner-operator's standards are not yet on 2022, follow theirs. If they are or are flexible, default to 2022.

Your existing P&IDs use inconsistent conventions for digital devices. If half your drawings show DCS function blocks one way and half another, the 2022 revision is a good lock point to standardize on. Update the legend across the drawing set in a coordinated MOC cycle.

Your engineering company is updating CAD templates. AutoCAD P&ID, SmartPlant, and AVEVA Diagrams all ship template libraries keyed to specific ISA editions. When the CAD vendor updates the library to 2022, propagating the update across active projects is the natural cycle to adopt the new edition.

Practical adoption

Wait for the next planned MOC cycle to migrate. Confirm your CAD tool ships a 2022-compatible symbol library before cutting over. Train the engineering team on the function-block annotation change because that is the most visible difference on a 2022 drawing. If a senior engineer reviews a 2022 drawing using 2009 expectations, they will flag legitimate diagrams as incorrect.

The bigger risk is running mixed-edition drawing sets indefinitely. The 2022 adoption itself is incremental. The cost of never adopting it compounds.

Related

• ISA 5.1 letter codes cheat sheet. Full first-letter and modifier-letter reference
• ISA letter index. First-letter reference pages with signal class examples
• P&ID to I/O list. Extract instrument tags and signal classes from your drawings
• Standards coverage. Which standards Tagsight recognises on extraction

FAQ

Which specific ISA 5.1 clauses govern the function-block annotation change.

The 2022 revision updates the graphical symbol tables and accompanying notes in the sections covering computing relays, function modifier Y and shared-display functions. The clause numbers are not reproduced here because ISA publishes the standard commercially. Consult your organisation's licensed copy. The key figures to compare are the instrument symbol table and the computing-device figure in both editions.

If I adopt ISA 5.1-2022, do I also need to update ISA 5.4 loop diagrams.

ISA 5.4 covers loop diagrams and is a separate standard. ISA 5.1-2022 does not require a simultaneous update to loop diagrams. However, if your loop diagrams reference the P&ID tag and panel-mounting convention, which most do, a drawing set that mixes 2009 and 2022 conventions may show inconsistencies between the P&ID and the loop diagram. It is practical to co-ordinate the update cycles, but it is not mandatory to update both at the same time.

How does the bus-segment annotation in ISA 5.1-2022 interact with IEC 61158 fieldbus standards.

ISA 5.1 is a drawing and identification standard, not a physical-layer or protocol standard. The bus-segment annotation it adds in 2022 is a graphical convention. A line style and label to indicate that a group of instruments share a digital bus. Which protocol that bus implements, Foundation Fieldbus H1, PROFIBUS-PA, HART multiplexed, etc. Is identified by the label on the segment, not by the ISA 5.1 drawing convention itself. IEC 61158 governs the protocol. ISA 5.1-2022 governs how you show it on the P&ID.

Does ISA 5.1-2022 affect SIS documentation or the IEC 61511 compliance package.

ISA 5.1-2022 changes drawing conventions, not functional safety requirements. SIS instruments should still be clearly identified on the P&ID as safety-function devices, typically by a different bubble shading, a specific tag prefix, SD, SV, ESDV, or a note referencing the SIL classification. These identification practices are governed by your project's SIS design basis and IEC 61511 requirements, not by ISA 5.1. The 2022 revision does not introduce new requirements for safety-instrument identification on P&IDs. It refines how all instruments, safety and BPCS are represented.

Our drawing set spans 20 years of revisions. Is it worth auditing for the ISA edition applied to each drawing.

If the drawing set is actively maintained and used for operations and modification work, yes. Drawings produced under different ISA editions may show the same instrument type with different symbols, which creates interpretation risk for engineers who are not familiar with all historical conventions. A controlled document register noting the ISA edition, and house standard revision applied to each drawing set is standard practice for operating companies managing long-lived facilities. It does not require re-drawing anything. It just makes the revision history explicit.