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PLC vs. DCS

At EPIC Automation, every practical, beneficial and cost-efficient automation solution we develop is based upon industry research and trends.  Before any design or development takes place, our engineers take the time to research and gain a thorough understanding of the process.  In October of 2011, Bill Lydon, Editor of Automation.com wrote an article called “PLC vs. DCS – Competing Process Control Philosophy.” Below we have built a table of the differences he sees between the two controls platforms:

PLC

DCS

Common Applications

Non-core process functions including material handling, water treatment, motor controls, balance of plant operations, air compressor controls, packaging, and other functions Core processes (food, pharmaceutical, refining, etc.)

Control Architecture

Programming Model“Loose” component architectures allowing functions to be easily added with hardware and software Configuration ModelMulti-disciplined controllers for logic, sequential and process control, HMIs, custom applications, and business integration on one platform.

Price

No Significant DifferenceCompetitive with DCS No Significant DifferenceCompetitive with PLC

Enterprise Interface

PLC applications have caught up to DCS in recent years and most interface to business enterprise systems for information interchange and synchronized operations DCS systems have tied into the enterprise for years, conforming to the Purdue Model and more recently the ISA95 standard

Asset Management

PLCs are playing catch up Provide integrated software for a full range of devices and asset management standards

APC Advanced Process Control

Beginning to add functions and break into process control Offer a number of tools for optimizing control loops and more advanced alternatives to improve performance of PID control.

Total Production Optimization

Can be approximated with loosely coupled software add-ons Real-time software modeling and control optimization is an emerging function

Sensor/Control Network Communications

PLC systems tend to have less refined interfaces to Foundation Fieldbus and HART. In many cases they rely on third party hardware and software with configuration being more labor intensive. DCSs have highly refined and integrated interfaces to Foundation Fieldbus and HART and adequate interfaces to other industrial automation networks

DCS Backbone Network 

PLC systems use open published protocols that are designed to cover a wide range of applications including simple discrete, synchronized motion control, motor control, and process. PLC suppliers continue to add options for redundancy. All control functions can connect to one Ethernet backbone (process control, discrete, motion control, safety; etc.) In DCS systems, the process networks (Foundation Fieldbus, HART) and PLC-oriented networks (DeviceNet, Profibus, Modbus, etc.) are connected to controllers, which are connected to the process DCS backbone. DCS systems generally have easier to apply redundancy solutions but the open networking standard groups such as ODVA and PI International have defined solutions for their protocols particularly with the initiatives for networked machine safety.

Skid & Packaged Systems

Provided by skid vendor. Usually require field engineering to configure and maintain N/A

 

EPIC is a multi-discipline engineering firm specializing in automation and line integration. Our group of engineers works with manufacturers to transform individual pieces of machinery and equipment into fully functional, integrated production lines. To learn more about EPIC’s capabilities, visit our website or contact an engineer today.

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EPIC Systems, Inc.
4134 Meramec Bottom Rd
St. Louis, MO 63129, US
314-714-1580