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  • 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.

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  • 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 onWhat 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

In previous discussions, we have presented detailed information about both SCADA and DCS

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