Industrial Network Basics: Simplifying I/O Terminology

There are many terms used for I/O technology in industrial automation: Remote I/O, Distributed I/O,  Modular I/O, Expandable I/O, Block I/O, Conventional I/O and the list can go on.  What do they all mean?  Can they be used interchangeably?  What is the difference?

Lets be honest… this is a muddled topic and many people use different things interchangeably.  I’ve done a bit of research and reading of automation magazines, forums and websites and have tried to piece it together.

Basically you have to think about it two ways:

  1. Where is the I/O located on the machine?
  2. How is the I/O collected from the machine?

Where is the I/O located?

Centralized I/O:
A majority of the I/O is located in the cabinet with the PLC and is situated on one continuous backplane.

Distributed I/O:
Small percentages of the I/O are located in many locations that are not the same as the controller.  This data is usually collected over an industrial network.  Distributed I/O solutions usually generate a total cost of ownership per point lower than other types.

Remote I/O: 
This has evolved over time but in 2011, I believe this is the new definition.   A big percentage of the I/O is in a single or few locations that are not the same as the location of the PLC.  It is a hybrid of Distributed and Centralized I/O solutions.  This data is usually collected over an extended backplane or an industrial network.

How is the I/O collected?

Conventional I/O:
Normally mounted inside a cabinet on DIN rail or rack; this utilizes a backplane providing communication and power supply to the I/O devices, which are unique to the version of the master device.  This is usually found in a centralized or remote I/O configuration.

Expandable I/O:
Found both inside and outside the cabinet, expandable I/O solutions utilize the “slice” concept and use a backplane/sub-bus to communicate between I/O devices, which are unique to the version of the master device.  These can implement large numbers of additional slices of different I/O types to be added including valve manifolds.  It is usually used in a remote I/O configuration.

Block I/O:
A set number of I/O points typically 8 or 16 discrete points.  Block I/O usually communicates over an industrial network and is rated for use on the machine, outside of a controls cabinet.  It is almost always found in a distributed I/O configuration.

Modular I/O:
Normally found outside the cabinet fitted with an industrial network communications head with the ability to combine multiple types of I/O devices, including valve manifolds.  Modular I/O is typically used in a distributed or remote I/O configuration.

Click here for a full line of Block I/O devices as well as Distributed Modular I/O devices.

Will Healy III is enthusiastic about smart manufacturing & workforce development. A Purdue University mechanical engineer, Will loves to share his passion for automation as a leader with Balluff Worldwide & Cincinnati's Advanced Manufacturing Industry Partnership. He speaks from experience about creating value through workforce, IIoT, sensors & automation solutions.

One Reply to “Industrial Network Basics: Simplifying I/O Terminology”

Leave a Reply