An I/O (Input/Output) list for a Distributed Control System (DCS), Instrumented Protective System (IPS/ESD), or Fire and Gas System (FGS) in the oil and gas sector is typically a comprehensive spreadsheet or database. It serves as a master reference for all instrument signals connected to these control and safety systems.
The format is a detailed table with specific columns that define every attribute of each input and output point.
Typical IO List Format
The document is structured as a table where each row represents a single I/O point. The columns detail the specific attributes of that point. While the exact columns can vary slightly between projects and companies, the following are standard.
| Column Header | Description | Example |
| Tag Number | The unique alphanumeric identifier for the instrument or I/O point. This is the primary key. | 10-PT-101A |
| Service Description | A brief, clear description of the instrument’s function or the process it measures/controls. | Pump P-101A Discharge Pressure |
| P&ID No. | The Piping and Instrument Diagram number where the instrument is shown. | PID-100-001 |
| System | The control system the I/O point is assigned to. | DCS, IPS, FGS |
| I/O Type | The type of signal. Common types include AI, AO, DI, DO. | AI (Analog Input) |
| Signal Type | The specific electrical signal characteristics. | 4-20mA, 24VDC, HART |
| Controller / Logic Solver | The specific controller, PLC, or logic solver that will process this I/O point. | DCS Controller 01 |
| I/O Card Type | The specific model number of the I/O card where the signal will be terminated. | AI-HART 8-Channel |
| Cabinet No. | The identification number of the system cabinet housing the I/O card. | DCS-CAB-01A |
| Slot No. | The specific slot or rack location of the I/O card within the cabinet. | 03 |
| Channel No. | The channel number on the I/O card to which the signal is wired. | 05 |
| Range (Low / High) | The engineering unit range for analog signals. | 0 / 10 |
| Units | The engineering units of measurement for the process variable. | barg |
| Alarm (LL/L/H/HH) | Setpoints for Low-Low, Low, High, and High-High process alarms. | 0.5 / 1.0 / 8.5 / 9.0 |
| Remarks | Any additional relevant information, notes, or special requirements. | Requires Intrinsically Safe barrier |
Key System Designations
DCS (Distributed Control System): Manages process control and monitoring. Handles standard analog and digital signals for regulating the plant.
IPS (Instrumented Protective System) / ESD (Emergency Shutdown): A safety-critical system (SIS – Safety Instrumented System) that takes automatic action to prevent hazardous events. Its I/O is separate and redundant from the DCS.
FGS (Fire and Gas System): Detects fires and combustible/toxic gas leaks and initiates alarms, suppression, and shutdown actions. It’s also a safety-critical system.
The I/O list is a foundational document used by multiple disciplines (Instrumentation, Process, Electrical, Automation) throughout the project lifecycle, from design and procurement to configuration and commissioning.