I/0 List

• I/O is an abbreviation for Input/Output.  I/O refers to any device that sends data to or from a PLC/DCS system. 
• An I/O list is a document that comprises a list of the Input and Output utilized in a control system.
• The I/O modules are linked to field devices such as sensors, transducers, actuators, control valves, and so on. These I/O modules are internally connected with the PLC/DCS system.
• The I/O list is generally referred as I/O list for PLC or I/O list for DCS.

• An I/O (In/Out) list is a document with a list of the instruments that information processing systems use to communicate to each other.
• Signals that are received by the system are its inputs, and signals that are sent by the system are its outputs. Any program, activity, or device that transfers data to or from a computer or another device is referred to as an I/O (In/ Out) list. One of the main deliverables of the CSI (Control System and Instrumentation) discipline is an I/O List.
• I/O list only displays the tag number that actually has a cable connecting to the control system. The I/O list must clearly state which instruments are assigned to which control system when there are many control systems in a plant or it may segregate the instruments into different sections of the document.

1. Tag number 
2. Loop Number 
3. Service description 
4. P&ID Number 
5. Type of Instrument 
6. Location 
7. I/O Signal Type 
8. Control System
9. Range of the instrument
10. setpoint value

The information in the I/O list column may be as simple as what is shown above, but some projects need the I/O list to be more detailed by including an alarm list, controller action, and logic “0”/”1″descriptor. I/O list would include I/O number assignment (rack, slot, channel number), which information would be supplied by the control system vendor.

To generate the I/O list, filter all tag numbers with an Input or Output from the instrument index.

• I/O list is used to determine the size of the control system necessary for a project by determining the number of I/O within a plant for each control system. It serves as the foundational material for designing PLC and DCS.
• The I/O List is used to specify the instruments’ input & output signal types. Inputs and outputs of PLC/DCS are categorized as follows:
  • Digital Output – DO
  • Analogue Input – AI
  • Digital Input – DI
  • Analogue output – AO