I/O List with Spare Calculation Template
A DCS or PLC I/O list that counts the analog and digital signals for you and adds the spare percentage, so you can size I/O cards straight from the list.
Download
- How to Use sheet with steps
- Template sheet, blank and ready
- Example sheet, filled in
- 10 built in formulas
- A4 landscape print setup
- Works in Excel, Google Sheets and LibreOffice
Preview of the Filled Example
This is the Example sheet from the download, so you can see exactly how the completed i/o list with spare calculation looks.
I/O list
| Sr | Tag | Description | I/O type | Signal | Range min | Range max | Unit | Controller | Rack | Slot | Channel | IS | HART | Alarms / remarks |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | PT 1101 | Steam header pressure | AI | 4 to 20 mA | 0 | 16 | bar g | CP 03 | 1 | 3 | 5 | N | Y | L 4, H 13, HH 14.5 |
| 2 | TT 2101 | Reactor jacket outlet temperature | AI | 4 to 20 mA | 0 | 200 | °C | CP 03 | 1 | 3 | 6 | N | Y | H 150 |
| 3 | FT 3101 | Feed flow | AI | 4 to 20 mA | 0 | 120 | m³/h | CP 03 | 1 | 3 | 7 | N | Y | |
| 4 | FV 3101 | Feed flow control valve | AO | 4 to 20 mA | 0 | 100 | % | CP 03 | 1 | 5 | 1 | N | Y | |
| 5 | PSH 1105 | Air receiver high pressure | DI | 24 V DC | CP 03 | 1 | 7 | 1 | N | N | Alarm on open | |||
| 6 | P 101 RUN | Feed pump running feedback | DI | 24 V DC | CP 03 | 1 | 7 | 2 | N | N | ||||
| 7 | P 101 START | Feed pump start command | DO | 24 V DC relay | CP 03 | 1 | 9 | 1 | N | N | ||||
| 8 | XY 4101 | Tank inlet SDV solenoid | DO | 24 V DC | CP 03 | 1 | 9 | 2 | N | N | Energised in normal operation |
About the I/O List with Spare Calculation
The I/O list defines every signal between the field and the DCS, PLC or SIS. It drives I/O card quantities, marshalling, cable schedules and the control system configuration, so errors in it multiply through the project. Automatic counts with spares make hardware sizing quick and traceable.
How to fill in this template
- Set the spare percentage at the top (20 % is a common project requirement).
- Enter one row per signal. A motor typically has several rows (run feedback, trip, start, stop).
- Choose the I/O type from the drop down so the counts work.
- Allocate rack, slot and channel once the I/O cards are selected.
- Use the totals with spare to decide how many I/O cards of each type to buy.
What the formulas do
- Count per type uses COUNTIF on the I/O type column.
- With spare = ROUNDUP(count × (1 + spare % ÷ 100)).
Related tools
Frequently Asked Questions
What is an I/O list?
A list of every input and output signal connected to a control system, with its type, range and hardware address.
How much spare I/O should I allow?
Typically 10 to 20 % installed spare, plus space for another 10 to 20 % future expansion. Check the project specification.
Why separate IS and HART columns?
Intrinsically safe and HART signals need specific I/O cards or barriers, so marking them makes card selection easier.
Learn more on the blog
IO list: 10 essential columns for a flawless DCS design
A practical guide on instrumentationblog.in that explains the procedure behind this template and how engineers apply it on real plants.
Read Full Article