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What if we had to reinvent the wheel each time we used it? That would certainly slow automotive manufacturers’ time to market. Under circumstances where something is created and then used more than once, it makes perfect sense to copy what already has been done, modifying it if necessary. So it goes with designing controls, at least at DuPont.
“Why reinvent the wheel?” said Karl Stevens, division engineering designer, instrumentation and controls, at DuPont Engineering. Along with Winfried Stach, global automation alliance manager at Siemens, Stevens explained “What You Do NOT Know About Design Guides” at the 2008 Siemens Automation Summit in Chicago.
“So easy a caveman can do it.” DuPont’s Karl Stevens explained how his company uses design guides to streamline and unify control system configuration processes.
“Why do we need a design guide?” asked Stach. “Most of us know that sometimes we want to reinvent the wheel so it’s ‘my own solution.’ If you have a good solution, then you don’t tell anybody. Then sometimes mistakes get into the design because people aren’t well-informed. That’s what the design guide should address. What are the strategies, and what should be the standard functionality of the system?”
Siemens provided the software that DuPont used to create its design guides. “We’ve created a joint engineering website,” explained Stach. “We wanted DuPont to write down the strategies and methods they were using. We want them to protect their investments and make sure their designs are the best way. A design guide is so easy a caveman can do it.”
But a design guide is only useful if it is used. “Now that we’ve written everything down, we have to make it work,” explained Stach. “The danger is you might end up with a mass grave of information.”
The main benefits of the design guide are reduced time and resources, design quality maintenance and assurance of a sound engineering level. This is accomplished by using it for front-end loading to estimate or specify the control system, for production design and for operation and maintenance. It can be used to help define and integrate control system technologies, to reduce the effort it takes to understand and implement the company’s control system requirements and to achieve effective control system life-cycle performance.
DuPont’s design guides, for example, include PCS 7 standard system documentation, hardware design, HMI design and a custom function block library. “The design guide’s custom library has function blocks and templates,” explained Stach. “An example of the HMI design guide includes the graphics environment, icons and faceplates, custom icons from the DuPont ‘typicals’ library and static graphics. For the hardware design guide, the major components are the drawings list and the Simatic PCS 7 features and specifications.”
“It’s good for estimating purposes,” explained Stevens. “But a design guide is a design guide,” he cautioned. “A standard is different. We have a lot of standards. But a design guide helps to cut down the design time, especially if you have the same PCS 7.”
Stach agreed. “This does not replace any standards,” he said. “We are only complementing standards.” He also warned that a design guide isn’t a mandate to retrofit a project to a design. The project is fixed, but the design still can be modified. “It depends on how much of the design guide you’re using,” explained Stach. “The reality is that every plant is different and projects can be different. We try to use the same drawings as often as possible, but that’s not always feasible.”
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