I/O List Excel Template. Columns and Format.
What columns belong in an instrument I/O list spreadsheet, how to structure it for loop checks, and the formatting mistakes that cause rework during commissioning.
**Download the free I/O list Excel template. ** pre-formatted with 14 columns, signal class dropdowns, and an example row.
A well-structured I/O list saves hours during commissioning. A poorly structured one creates confusion, delays loop checks, and forces rework when the control system integrator can't map your tags to their hardware.
Essential columns
Every I/O list should include these columns at minimum.
| Column | Purpose | Example |
|---|---|---|
| Tag Number | Unique instrument identifier per ISA 5.1 | FIT-101, PSL-201 |
| Loop Number | Groups related instruments | 101, 201 |
| Instrument Type | ISA function letters | FIT, PSL, TIC, XV |
| Signal Class | AI, AO, DI, or DO | AI |
| Description | What the instrument does | Flow Indicating Transmitter |
| P&ID Reference | Source drawing number | PID-001-A |
| Page Number | Page within the drawing set | 3 |
| Service, Process Area | Plant area or unit | Cooling Water, Unit 200 |
These eight columns are the foundation. Without any one of them, someone downstream will have to go back to the drawings.
Columns that save rework later
Beyond the basics, these columns prevent the most common back-and-forth during detailed design.
| Column | Why it matters |
|---|---|
| Connected Equipment | Which pump, vessel, or exchanger the instrument serves, P-101, V-200 |
| Range, Span | 0-100 PSI, 4-20mA, needed for scaling in the PLC |
| Fail Position | FC, FO, FL for valves, critical for safety reviews |
| Cable Type | Shielded pair for analog, standard for discrete |
| Panel, Cabinet | Where the signal terminates, needed for cable scheduling |
| I/O Module | Which PLC card the signal lands on |
| Alarm Setpoints | High, Low, HH, LL values if known |
| Notes | Field conditions, special requirements, deviations from standard |
You don't need all of these on day one. But if you structure your spreadsheet to accommodate them from the start, you avoid reformatting later.
Full 14-column reference
The free I/O list template ships with 14 columns. Here is what each one does and where the data comes from.
| # | Column | Description | Source |
|---|---|---|---|
| 1 | Tag Number | Unique instrument identifier. Format must match the P&ID exactly, including separator style, FIT-101, not FIT101. Primary key for all downstream joins. | P&ID |
| 2 | Loop Number | Numeric or alphanumeric identifier grouping the transmitter, controller, and final element in a control loop. FIT-101, FIC-101, and FCV-101 all carry loop 101. | P&ID |
| 3 | Instrument Type | ISA 5.1 function letter string. FIT Flow Indicating Transmitter. PSL Pressure Switch Low. TIC Temperature Indicating Controller. | P&ID plus ISA table |
| 4 | Signal Class | AI, AO, DI, or DO. This column drives PLC module selection and cable type. See classification rules below. | Engineering judgment |
| 5 | Service, Description | Plain-language description of what the instrument measures or controls. "Cooling water supply flow" is more useful than "flow" to a loop-check technician. | P&ID plus P&ID notes |
| 6 | Equipment Tag | The pump, vessel, exchanger, or compressor the instrument monitors or controls. P-101, V-201, E-305. Used by procurement and the equipment list. | P&ID |
| 7 | Line Number | The pipe segment the instrument sits on. 4"-CS-101-A1A. Cross-references the line list. | P&ID |
| 8 | Range, Low | Lower range value in engineering units. 0 PSI, -40 degC, 0 m3, h. | Datasheet, P&ID spec |
| 9 | Range, High | Upper range value in engineering units. 100 PSI, 200 degC, 500 m3, h. | Datasheet, P&ID spec |
| 10 | Units | Engineering units for the range. PSI, kPa, degC, m3, h, %, mA. Be explicit. "pressure" without units is not useful for PLC scaling. | Datasheet, P&ID spec |
| 11 | P&ID Drawing | Drawing number of the P&ID where the instrument appears. PID-001, 2034-P-001. | P&ID title block |
| 12 | P&ID Sheet, Page | Page or sheet number within the drawing set. Especially important for large multi-sheet P&IDs. | P&ID |
| 13 | BPCS, SIS | Flag indicating whether the instrument belongs to the Basic Process Control System or the Safety Instrumented System. SIL-rated instruments must be separated. | SIL study, design basis |
| 14 | Notes | Free-text field for deviations, special requirements, field conditions, or open items. "Requires explosion-proof housing, Zone 1". | Engineer |
Worked example rows
Three instruments from a separator skid, showing how the columns fill in for different signal classes.
| Tag | Loop | Type | Class | Description | Equipment | Range Low | Range High | Units | Drawing | Sheet | BPCS, SIS |
|---|---|---|---|---|---|---|---|---|---|---|---|
| FT-101 | 101 | FIT | AI | Separator inlet flow | V-101 | 0 | 500 | m3, h | PID-001 | 1 | BPCS |
| PT-2034A | 2034 | PIT | AI | Separator operating pressure | V-101 | 0 | 1600 | kPa | PID-002 | 3 | BPCS |
| LSH-405 | 405 | LSH | DI | Separator high-high level switch | V-101 | , | , | , | PID-002 | 3 | SIS |
| LCV-405 | 405 | LCV | AO | Separator level control valve | V-101 | 0 | 100 | % | PID-002 | 3 | BPCS |
| XV-410 | 410 | XV | DO | Separator inlet shutoff valve | V-101 | , | , | , | PID-002 | 4 | SIS |
Note that LSH-405 and XV-410 both carry the SIS flag. They require separate marshalling, separate I/O cards, and separate cabinet sections from the BPCS instruments in the same loop.
Formatting standards that matter
Consistent tag numbering
Pick a format and enforce it across the entire list. Mixed formats cause duplicate entries and missed instruments during QA.
| Consistent | Inconsistent, problems |
|---|---|
| FIT-101 | FIT-101 |
| FIT-102 | FIT102, missing separator |
| FIT-103 | Fit-103, mixed case |
| PSL-201 | PSL-0201, zero-padded vs not |
Signal class validation
Every instrument must map to exactly one signal class. Common errors.
- Control valves left as AI. A valve with a 4-20mA positioner input is AO, not AI. The signal goes to the valve.
- Switches classified as AI. A pressure switch, PSL, PSH is a discrete contact. That's DI, not AI.
- Solenoid valves as AO. Solenoids are on, off. That's DO.
- Indicators with no wiring. A local gauge, PI, TI with no transmitter may not be wired to the DCS at all. These need to be flagged, not classified.
Conditional formatting
Color-coding signal classes in Excel makes QA review significantly faster.
| Signal Class | Recommended Color | Rationale |
|---|---|---|
| AI | Blue fill | Convention in most I&C departments |
| AO | Green fill | Output action green |
| DI | Amber, Orange fill | Discrete input alert, status |
| DO | Red fill | Discrete output command |
This isn't cosmetic. It lets reviewers scan hundreds of rows and spot classification errors visually.
Use Excel's conditional formatting rules, Home > Conditional Formatting > New Rule > "Format cells that contain specific text" and apply them to the Signal Class column. Lock the rule so that new rows inherit it automatically when inserted.
A secondary use for conditional formatting. Highlight any row where the BPCS, SIS column is blank. An unflagged instrument is a gap in the SIS segregation audit.
Handling multi-channel devices and fieldbus instruments
Some instruments produce more than one signal. A dual-output transmitter or a HART device reporting two process variables occupies two I/O channels but has one physical tag. The correct approach is one row per channel, with the same tag number and a channel suffix noted in the Notes column, for example, FT-101 channel 1 AI for flow, FT-101 channel 2 AI for pressure from the same sensor.
For fieldbus instruments, PROFIBUS PA, Foundation Fieldbus, HART multidrop, the mapping is different. Each device still appears as one row, but the Signal Class column uses a fieldbus identifier rather than AI, AO, DI, DO. Add a Protocol column to carry the distinction. Fieldbus segments share a single twisted-pair cable, so grouping instruments by fieldbus segment in the Notes or a dedicated Segment column is essential for the cable schedule.
Naming spare and undefined channels
Spare I/O channels reserved for future use should appear in the I/O list with an explicit spare tag format. Common conventions include SPARE-AI-001 or SPA-001-AI. Naming them has two benefits. The PLC programmer can create a placeholder tag and prevent access to that address, and the cable schedule can reserve a terminal in the marshalling cabinet without leaving blank rows.
Channels reserved for known-but-not-yet-designed instruments should use a preliminary tag, PRE-101 or TBD-101 rather than being left blank. Blank rows in an I/O list get sorted out, filtered out, and lost.
Common mistakes that cause rework
1. Duplicate tag numbers
Two instruments with the same tag number will cause conflicts in the PLC program and the cable schedule. This happens most often when.
- Multiple engineers work on different sections of the same P&ID set
- Tags are copied from a similar project and not fully renumbered
- Revision changes add instruments without checking existing numbering
Run a pivot table on the Tag Number column before issuing any revision. Flag any tag that appears more than once.
2. Missing loop numbers
Without loop numbers, you can't group related instruments, transmitter, controller, valve into control loops. This makes the loop check procedure nearly impossible to organize.
3. Inconsistent separators
FIT-101 vs FIT_101 vs FIT101. Pick one. Mixed separators break sorting, filtering, and VLOOKUP formulas. They also cause false "missing instrument" flags during QA when the formats don't match across documents.
4. Orphaned valves
A control valve, FCV, TCV, PCV should have a corresponding transmitter and controller in the same loop. If your I/O list has a valve with no transmitter, either the transmitter is missing from the list or the valve tag is wrong.
Filter the I/O list for AO rows and cross-check each against the corresponding AI in the same loop. Missing AI with a present AO is an orphaned valve.
5. No page reference
When someone finds an error in the I/O list, they need to go back to the source drawing. Without a page number column, that means flipping through an entire drawing set. On a 50-page project, that's a significant time cost per correction.
6. Mixing wired and non-wired instruments
Local gauges, sight glasses, and manual valves often appear on P&IDs but have no electrical signal. Including them in the I/O list without a clear flag inflates your I/O count and leads to phantom channels in the PLC configuration.
7. Mixing AI and AO codes for HART devices
HART communicators sit on 4-20mA analog loops. The signal class is still AI, for transmitters or AO, for positioners. HART is a protocol, not a signal class. A column marked "AI, HART" is not a valid signal class. Keep Signal Class as AI or AO and add a Protocol column for HART, with the device address noted separately.
8. Blank units on analog channels
A range of "0 to 100" with no units column is meaningless to a PLC programmer scaling a raw analog count to engineering units. Every AI and AO row must carry units.
Structuring for PLC import
If your I/O list will feed into PLC programming software, TIA Portal, Studio 5000, etc. structure matters even more.
- Tag numbers must be valid variable names. No spaces, no special characters beyond hyphens and underscores
- Signal class determines the module type. AI maps to analog input cards, DO maps to discrete output cards. Getting this wrong means wrong hardware orders.
- Group by cabinet, panel. PLC programmers organize by physical location, not by process area. Include a termination column early.
For direct export to TIA Portal or Rockwell L5X format, see P&ID to TIA Portal XML and P&ID to Rockwell L5X.
Quick checklist before submitting
Before sending an I/O list to the next discipline.
- Every row has a tag number, loop number, type, signal class, and description
- No duplicate tag numbers, sort and scan, or pivot
- Signal classes are correct, valves AO or DO, switches DI, transmitters AI
- Page references point to the correct P&ID revision
- Conditional formatting applied for visual QA
- Filter each signal class column and verify the counts match your expectation
- Check for orphaned control loops, valve without transmitter, or vice versa
- Every AI, AO row has range low, range high, and units populated
- BPCS, SIS column populated for every row
- Spare channels named, not blank
For larger projects, see how to validate an I/O list against P&IDs for the full reconciliation procedure. The full column-by-column build sequence and controlled-document conventions are covered in the I/O list creation guide. For a detailed walkthrough of what each standard I/O list column carries and where the data comes from, see I/O list columns explained.
FAQ
What is the correct signal class for a HART transmitter.
AI, the same as a standard 4-20mA transmitter. HART rides on the 4-20mA loop using frequency-shift keying on top of the DC signal. The PLC I/O card sees an analog input. Add a separate Protocol column to distinguish HART from non-HART devices, and include the HART address if using a HART multiplexer. The Signal Class column should only contain AI, AO, DI, or DO.
How many channels does a dual-output transmitter consume.
Two. A transmitter reporting flow and density on separate analog outputs occupies two AI channels in the PLC. Create two rows with the same tag number, distinguishing them by a channel suffix in the Notes column or by adding a Channel column. The cable schedule still shows one cable from the field device, but the marshalling panel fans out to two I/O terminals.
Should SIS instruments appear in the same spreadsheet as BPCS instruments.
They can appear in the same workbook, but they must be on separate sheets. Mixed SIS and BPCS entries on a single sheet will fail a SIL verification audit. The SIS I/O list is typically maintained by the functional safety engineer and issued as a separate controlled document with its own revision history. Cross-reference by tag number where instruments appear in both systems, a common case for voting transmitters in 2oo3 configurations.
How do I handle instruments that appear on multiple P&ID sheets.
The instrument index entry is unique. The tag appears once regardless of how many sheets reference it. In the I/O list, record the sheet where the instrument bubble originates, not secondary references. Off-page connectors on other sheets point back to the originating page. If you cannot determine the originating page, check the drawing index for the legend page or general arrangement P&ID.
When should I start populating the range and units columns.
As early as the data is reliable. In FEED, ranges are often preliminary estimates from the process datasheet. In detailed engineering they should be confirmed values from the issued-for-purchase instrument datasheet. Mark preliminary values with a flag in the Notes column, for example, "preliminary, confirm at IFP". The PLC programmer needs confirmed ranges before the loop program can be finalized. Having placeholder values prevents the column from being forgotten.