In this video, we’re going to talk about “Remote I/O” and “Distributed I/O”.
Depending on who you talk to,
some say “Remote I/O and Distributed I/O
are the same thing and the terms are interchangeable”…
“Not so” says others.
So, who’s correct?
Let’s investigate the history of the terms
“Remote I/O” and “Distributed I/O”
and discuss what they mean today.
Let’s go back a few decades to early computerized control.
The predecessor of the DCS and the PLC
was the “Direct Digital Control” or “DDC” system,
only seen today in museums.
Many vendors such as “Taylor Instruments”, “Bailey Control” and “Foxboro”
had DDC systems that centered on a mini computer
connected to several proprietary I/O devices
located at “Remote” locations around the plant.
Today’s DCS is a control system that has a number of “Distributed” autonomous controllers
each operating a number of continuous operations.
The controllers are tied together via a centralized supervisory controller.
We’ve already used the terms “Remote” and “Distributed”
in the context of locations of both I/O and controllers.
It’s easy to see how the terms can be misunderstood.
OK. Let's have a look at “Remote I/O”
and “Distributed I/O” from a PLC perspective.
“Remote I/O” means that the I/O module
is at a “remote” place physically located a distance from the control PLC.
As we mentioned earlier “Remote I/O”
is sometimes also referred to as “Distributed I/O”.
Let’s look at a definition for “Distributed I/O”
that differentiates it from “Remote I/O”.
Generally speaking, Distributed I/O has a “brain”
or some computing capacity. By default, it is Remote.
Allen Bradley has “FLEX I/O”
which is a modular I/O system for distributed applications.
The Flex I/O allows for the connection of up to eight I/O modules
and transfers I/O data to and from a central controller or PLC.
Flex I/O is an example of “Distributed I/O”
and the eight modules connected to the Flex I/O
are examples of “Remote I/O”.
Siemens has the “ET 200SP” series of Distributed I/O
that can connect up to 16 channels of digital or analog I/O
with a single wire connection.
The “ET 200SP” is an example of “Distributed I/O”
and is connected to the bus system via an interface module.
This system is very flexible
as it can accommodate either PROFINET interface modules
or PROFIBUS interface modules.
As we said earlier, Remote I/O
is at a “remote” place physically located a distance from a control PLC.
Remote I/O does not have a “brain”
and is not capable of any computing function at all.
It’s likely safe to say that when you hear the term “Remote I/O”
there is only one controller, or PLC, involved
as opposed to “Distributed I/O” which has multiple controllers.
Let’s review…
The predecessor of the DCS and the PLC
was the “Direct Digital Control” or “DDC” system
which centered on a mini computer connected to several proprietary I/O devices
located at “Remote” locations around the plant.
A modern DCS is a control system
that has a number of "Distributed" autonomous controllers.
Generally speaking, Distributed I/O has a “brain” or some computing capacity.
Remote I/O does not have a “brain”
and is not capable of any computing function at all.
The term “Remote I/O” suggests a single controller such as a PLC,
whereas the term “Distributed I/O” suggests multiple controllers.
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