Choosing a control system: PLC or DCS

Today, the economic pressures facing us are at levels few have ever seen. These challenges make it all the more imperative to select the technology that is right for you. Focusing on the requirements of the application and of the key stakeholders should always be your guiding principle.

03/01/2009


Today, the economic pressures facing us (and our companies) are at levels few have ever seen. These challenges make it all the more imperative to select the technology that is right for you. Focusing on the requirements of the application and of the key stakeholders (engineering, maintenance and operations) should always be your guiding principle. No one can afford to select a system based solely on technology (what it can do). More importantly is what it can do for you. Productivity, efficiency, safety, energy savings and long-term supportability are among the criteria that should guide your decision.

Many of the classic stereotypes of when to use a programmable logic controller or when to use a distributed control system have become clouded. In fact, the key differences between a PLC and DCS are no longer in the hardware. Microprocessor advancements have made the controller in a PLC system virtually indistinguishable from that in a DCS. The real differences now are in the software and in the application libraries (domain expertise) that come with these products.

To help determine the best technology for your application it is important to objectively document your requirements. To enhance this process, ask some important questions of the major stakeholders in the plant. This will help you determine whether a PLC or DCS system is best for you.

Production

  • Downtime %%MDASSML%% Does it result in lost production or does it additionally create dangerous conditions for the equipment and personnel?

  • Batch %%MDASSML%% Is the process a “simple” batch application (single product, single procedure) or “complex,” requiring a high level of flexibility and recipe management?

  • Type of control %%MDASSML%% Does the process require high speed control such as fast interlocking or motor control, or does it require deterministic execution of analog control logic such as PID?

    • Operations

      • Role of the operator %%MDASSML%% Does the operator primarily handle exceptions or are they an integral part of the process (the person in the loop)?

      • HMI displays %%MDASSML%% Is the main purpose to display status information (On/Off, Run/Stop) or to provide a window into the process (using faceplates and analog trends)?

      • Alarming %%MDASSML%% Does the operator need exception-based information or management tools to help respond quickly and effectively to process upset conditions?

        • Maintenance

          • Configuration changes %%MDASSML%% Can the system be shutdown or must changes be made online without affecting operation of the process?

          • Diagnostics and troubleshooting %%MDASSML%% Is the maintenance team looking for diagnostics to tell them when something is broken or asset management capabilities to alert them before something might break?

            • Engineering

              • Configuration languages %%MDASSML%% Is the preferred tool for configuration and troubleshooting ladder logic or function block?

              • Philosophy %%MDASSML%% What is the mindset: programming of custom logic or configuration and reuse of pre-engineered templates?

              • Project engineering approach %%MDASSML%% Is it a “bottom up” or “top down” design and configuration?

                • Many applications require functionality that combines the capabilities of a traditional PLC %%MDASSML%% such as programming in ladder logic and the ability to perform high-speed control of motors and drives, and the classic DCS %%MDASSML%% such as PID control and redundancy. We call these hybrid applications. If you fall into this category, the good news is that there are hybrid systems on the market. No financial bailout is needed to produce hybrid technology for process applications.

                  The role of technology is to help people perform their jobs quicker, easier, safer and more productively. Keep this in mind as you evaluate which technology to add to your plant.


                  <table ID = 'id1499270-0-table' CELLSPACING = '0' CELLPADDING = '2' WIDTH = '100%' BORDER = '0'><tbody ID = 'id1499190-0-tbody'><tr ID = 'id1499192-0-tr'><td ID = 'id1499194-0-td' CLASS = 'table' STYLE = 'background-color: #EEEEEE'> Author Information </td></tr><tr ID = 'id1499320-3-tr'><td ID = 'id1499322-3-td' CLASS = 'table'> Todd Stauffer is DCS marketing manager, and Bob Nelson is PLC marketing manager at Siemens Energy & Automation Inc. </td></tr></tbody></table>


No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
World-class maintenance: The three keys to success - Deploy people, process and technology; 2016 Lubrication Guide; Why hydraulic systems get hot
Your leaks start here: Take a disciplined approach with your hydraulic system; U.S. presence at Hannover Messe a rousing success
Hannover Messe 2016: Taking hold of the future - Partner Country status spotlights U.S. manufacturing; Honoring manufacturing excellence: The 2015 Product of the Year Winners
The digital oilfield: Utilizing Big Data can yield big savings; Virtualization a real solution; Tracking SIS performance
Getting to the bottom of subsea repairs: Older pipelines need more attention, and operators need a repair strategy; OTC preview; Offshore production difficult - and crucial
Digital oilfields: Integrated HMI/SCADA systems enable smarter data acquisition; Real-world impact of simulation; Electric actuator technology prospers in production fields
Improving flowmeter calibration; Selecting flowmeters for natural gas; Case study: Streamlining assembly systems using PC-based control; CLPM: Improving process efficiency, throughput
Putting COPS into context; Designing medium-voltage electrical systems; Planning and designing resilient, efficient data centers; The nine steps of designing generator fuel systems
Warehouse winter comfort: The HTHV solution; Cooling with natural gas; Plastics industry booming

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
This article collection contains several articles on the vital role that compressed air plays in manufacturing plants.
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.
This article collection contains several articles on strategic maintenance and understanding all the parts of your plant.
click me