Picture an operator in the control room of a chemical plant. As his or her eyes scan the HMI screenswww.cechina.cn, they pause briefly on the indication for a tank level measurement. Can the operator tell how that measurement got from the sensor to the control system? The answer is probably no, and the operator doesn't care anyway. As long as the information is correct and timely, how it got there is not a concern. It's transparent to the people running the plant.
　　That bit of level information could be sent via analog wiringCONTROL ENGINEERING China版权所有, digital wiringCONTROL ENGINEERING China版权所有, fieldbus, or wireless. The choice of transmission technique should represent a balance of cost and reliability within the plant context. Wireless networking has entered into that equation in new ways over the last few years and changed the balance dramatically. All of which raises the question: Does integrating wireless into a larger existing plant control environment represent a new challenge to control architecture?
　　Fieldbus revisited?
　　When HART and fieldbus networking platforms emergedCONTROL ENGINEERING China版权所有, they had much promiseCONTROL ENGINEERING China版权所有, but were not immediately attractive to operators since implementation required upgrades to both hardware and software. Wireless system providers took note of this lesson, and have done much to avoid reliving those difficulties.
　　"It has to be so simple that my mother can use itCONTROL ENGINEERING China版权所有," says Bob Karschnia, VP of wireless business for Emerson Process Management (EPM). "The technology has to be invisible, so we've spent a higher amount of time making sure it's easy to use than we typically would. We wanted to make it so you can put it into your legacy systems because, without that, you run into the situation where you have to upgrade your whole DCS to use wireless.
　　"Otherwise you're no different than you were with Foundation Fieldbus, which meant that you had to make a radical change to your plant architecture and devices to make it work. We've tried to build this so that it migrates easily into existing systems."
　　Easy, yes, but users