PLC & DCS differences

PLC or programmable logic controlleris a robust computer used to automate processes.A DCS or distributed control system is similar to a PLC that it has robust computer controllers

However, DCS contains multiple autonomous controllers
distributed throughout the system,
It is also used to automate processes.
You may have read it and said, "So what's the difference?"
To answer this question,
we have to go back more than 40 years.
After several years in a corner design office,
this guy Dick Morley quit his job
after asking his employer to allow him to work on Saturdays instead of Fridays,
who refused.
You see, Mr. Morley loved skiing, but he found that the weekends were too crowded for his tastes.
Due to financial obligations and the like,
Mr. Morley and a friend formed Bedford Associates
where they wrote sentences,
for local tool companies, which wanted to evolve into the new stage of solid state production.
These proposals used small computers,
seemed to be repetitive in nature,
and from one project to another,
there were many similarities.
Eventually Mr. Morley got bored of writing proposals,
due to its repetitive nature,
and began to wonder if he could create an auditor who could handle these day-to-day tasks.
In fact, during his dismissal, Mr. Morley created a blueprint
for a proposed programmable controller and got it on his team.
They started designing the programmable controller.
After finding financial support,
the company, Modicon was created.
Without Modicon knowledge and during the design phase of the programmable controller,
a man from GM had presented a newspaper,
a request, for a solid state controller that will make the plants more reliable and durable,
which would also replace wired relay systems
spread to the manufacturing industry.
As the story goes, some time later,
GM is hearing about the work being done at Modicon
and final contracts with them for the purchase of over $ 1,000,000 in PLC
(then, auditors were called programmable auditors
and the "Logic" section of the current name
was not added until the dawn of personal computers or computers).
Modicon was later baptized and quickly became a business.
The name has persisted in a few acquisitions,
the latest and current is Schneider Electric.
In the beginning, the PLC was mainly used for discrete controls.
Ultimately, the big market from GM for the replacement of wired relay systems.
The programming of the PLCs was mainly in the logic of the ladder,
which is a form that looks a lot like a schematic.
The PLC received device information from the field,
solved the logic and then activated the outputs to produce the desired result.
In essence, the PLC was invented to perform repetitive tasks in a reliable and robust manner.
As for DCS, around 1975 some companies released a version of a DCS.
Basically, the creation of a DCS system was due to the increasing use of microcomputers.
There were other computer-based systems in the industry
from the late 1950s, but had limited capabilities
for scalability, durability and safety.
There were many benefits to a DCS, but one of the main draws
was that an entire factory could be connected through proprietary communications
and is controlled by a distributed system.
For example, suppose you had a plant that made an ice cream sandwich.
The factory will have a production line for ice cream
and one of the standalone inspectors would process the batch of ice cream.
After the ice cream batch is complete,
Another standalone controller can process the freezing of this ice cream.
Another controller can process the cookie batch,
while another may oversee the baking process.
With several autonomous auditors,
if one auditor failed, it would affect only this process and not all the others,
leading to a powerful system that virtually eliminated all plant failure.
DCS was really good at autonomous control of single or multiple processes.
Another important benefit of DCS was integrated monitoring
and a control system similar to current SCADA systems.
The reason it's a big benefit is that the whole label base is there,
has already been set up to control the process,
available for use on monitoring and control screens.
DCS also had operating block programming.
Program block operation, if you are not familiar with,
is a section or multiple lines of code behind a single interface.
This interface can do something like operate the manual
and automatic valve operation.
Operation block programming saves a lot of time and unnecessary programming.
In fact, the difference 40 years ago was significant
and if you had a large factory with continuous processes,
you would probably have chosen a DCS.
In today's industries, DCS and PLC are quite similar,
storage for integrated monitoring and control.
With open source communications, fiber optics,
Ethernet and the like, many PLCs can now communicate with each other
and be autonomous PLCs communicating over the network to other autonomous controllers.
This wide communication would allow the control of individual or multiple processes
from one PLC to communicate with another PLC.
See the example of an ice cream sandwich.
PLC-A could process ice cream.
When the batch is completed,
The PLC-A would communicate with the PLC-B that the process was complete
and PLC-B could then start the freezing process.
You can see it with today's technologies,
a wide and robust PLC system could do almost the same thing that DCS can do.
One advantage of DCS is the installation cost.
This advantage arises due to the position of the autonomous controller
in the process may be close to pulling large sections of I / O cables in an installation.
Another advantage is the integrated monitoring and control system.
One of the disadvantages of DCS is the lack of developers
who have some experience with a DCS.
Most flooring technicians are familiar with ladder programming
However, DCS developers and technicians
usually need more specialized experience in database operations
as well as computer-related networking knowledge.
Due to specialized training,
DCS developers are a little harder to find.
Speaking of advantages, today's PLC systems can have almost the same as DCS,
excluding supervisory control and data acquisition (SCADA).
With PLC system (multiple PLCs in factory structure),
you need to set up the monitoring and control system.
The entire DCS database would be available to set up the monitoring and system,
PLC systems individual PLC databases must be created in SCADA system software.
There are more developers available for rent in the PLC arena
and with new programming languages ​​such as blockchain,
sequential operation, etc., the advantage of operating block programming is no longer exclusive to DCS.
This saves development time when planning a PLC.
As you can tell, there are potential advantages and disadvantages to both systems.
The subtraction is that with today's technologies,
Each system can control an entire factory.
Which system will be chosen will probably have the advantages
and disadvantages, as well as the cost of the system.
In summary, DCS has standalone controllers scattered throughout the installation.
If one controller fails, the whole factory is not necessarily affected.
It also has on-board control and control
which saves development time.
A single PLC is a single point of failure.
You certainly would not want to control an entire factory with a single PLC
however; a connected PLC system can have almost the same safety and durability as a DCS.