In previous discussions, we have presented
detailed information about both SCADA and DCS which you can find the links to these
videos in the description area. In this conversation, we will
contrast and compare both systems. Here at RealPars, we love making videos that
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you’ll never miss another one! As you have previously learned, a SCADA system is a collection of
both software and hardware components that allow supervision and control of
plants, both locally and remotely. A DCS is also a collection of
components used for the same purpose. These similarities may lead you to ask
then: Are they essentially the same? To answer that question let’s look back
to the fundamentals of both systems. You may recall that a SCADA system is used
to gather and present data to operators, make decisions about processes
with the aid of operator input, and control plant functions
based on those decisions. The DCS’s role in plant automation
is the same as the SCADA system. Since we already know that the role of the SCADA
and DCS systems are essentially the same, let’s try to compare and contrast the
mechanisms used to handle those tasks versus the operations themselves. Let’s start with the device that plant personnel
use to interact with the automated processes. Human Machine Interface (HMI) panels are the primary graphical interface between
the plant processors and processes and the operators interacting with
and controlling those processes. We had provided a video
previously on “What is an HMI?”. You can follow the link to this
video in the description area to watch it and grasp more information
about Human Machine Interfaces. The HMI panels can be procured from the same
manufacturer as the controller,such as Siemens, Allen Bradley, GE, and Schneider Electric, all
of which produce their brand of HMI panels. There are also independent HMI panel
manufacturers such as Red Lion. Yet still, the HMI can be an
industrial computer from Dell or any other manufacturer that meets
the rugged requirements for the PC. While most of the manufacturers
may have their own brand of HMI, typically, additional software
is needed to program the HMI. In the case of Siemens, WinCC software,
Allen Bradley requires FactoryTalk View, Schneider needs Vijeo Designer
or Citect, and so on. There may be some PLC/HMI programming software that is integrated for the
manufacturer but for the most part, they are separate software packages
requiring separate purchases. Having the same vendor of PLC and HMI may
seem to be an advantage but as noted, the requirement for additional
software is definitely not beneficial. You would also think that using the same manufacturer would
allow you to have the tag database of your processor available for use in the
HMI, not necessarily true. Some vendors do have drag and
drop capabilities, such as GE. However, most of them require
exporting and importing while others require the creation
of the tags entirely from scratch. HMIs are primarily used in small
scale automation environments. When you have larger-scale systems, the interface with the plant process
is typically a desktop computer. This computer requires
its own software package such as Intellution or iFix,
Wonderware, or VtSCADA to name a few. While a SCADA system has HMIs or computers that
are not necessarily of the same manufacturer, the DCSs have graphical interfaces that are
typically integrated within the DCS system. As you can imagine, this is a definite plus as the requirement for additional
software is not needed. And, as a bonus, the tags within the DCS are
available for use, without much additional effort. Based on the interface
descriptions of SCADA and DCS, clearly, the DCS has the
advantage in this category. Now let’s discuss the
brains of the operation. Within the SCADA system,
there may be PLCs and RTUs. As you are aware by now, these
components require programming in order to execute commands
essential to plant operations. Earlier in automation history, there may have been thousands of lines of
code to run a single process in a plant. As the years have gone by, more and more ways to
consolidate and reuse code have been implemented. This reusable code still needs to be written
in a format that is used by the controller. Custom function blocks, Add on Instructions (AOIs),
etc.,written in the controller by a programmer. Once written, the code can be instantiated any
number of times for use within the controller. It may take quite a while to develop a library
of code that can be used over many projects. While this was, at least in the earlier days,
more cumbersome in the SCADA implementation, the DCS had many predefined
functions that could be customized and deployed for various applications. This didn’t eliminate the need to write code
however,it did help to facilitate faster integration because less time would be spent writing
code for commonly used functions. Processing times are somewhat slower in the
DCS versus the PLC/RTU SCADA environment. While this is not necessarily problematic, it could have an impact on processes
that are very time sensitive. Communications within a SCADA
system can vary widely and have adapted to the changing
technologies while the DCS has also adapted, there are still some proprietary
communications that can be challenging. It has been said that if safety is a
priority then the DCS is the route to go. However, nowadays, with the abundance of safety
processors, a SCADA system may also be selected. To sum things up, in today’s market, there
are not massive differences in the systems. DCSs have integrated operator interface
software with tag databases, while SCADA requires you to purchase additional
software and build or import your tags. If you have a very time sensitive process, SCADA systems may have a slight advantage
as the processing time is faster. Need an open communication architecture?
Advantage SCADA. Concerned about safety? Advantage DCS. As you can see, there are a lot of
similarities between the two systems. Either way you go, hopefully this video has
shed some light on both the similarities and differences between the two systems. Want to learn PLC programming
in an easy to understand format and take your career to the next level? Head on over to realpars.com
