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发表于 2009/11/10 17:23:58

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新设备用有线扩展即可?

One of the things I omitted from the earlier discussion about the wireless panel was a brief exchange between Patrick Schweitzer and Dave Kaufman (ExxonMobil and Honeywell, respectively) on the nature of wired devices. Kaufman was trying to contrast the finite nature of wireless bandwidth with the notion that there is no limit to wired devices because you can always run more wire. Schweitzer’s body language suggested he had a problem with that last statement, so I asked him to elaborate.

Schweitzer said that you can’t always add more wire, because there simply may not be enough room. There are physical limits to the number of cables you can stuff into your trays, terminate in your cabinets, etc. That reminded me of statements made by Mike Miller and Ray Price from Duke Energy in an old podcast. (Sorry, it’s no longer available in our catalog.) I dug out my archive copy and listened to it again. One of the constraints they faced when they wanted to add new instrumentation points to an existing nuclear power plant was the difficulty of pulling new cabling. The complexity of tunnels and passages for cables made that virtually impossible, so the plant expanded its capacity by turning some of the existing device cables into fieldbus segments, so one cable could communicate with a group of devices.

Lately, I suspect few plants have been bumping up against limitations for adding new devices. However as we emerge from this downturn and plants begin to spend money again (I hope), the thought of upgrading legacy installations will again come to the fore. The number of options for adding and upgrading instrumentation and control infrastructure is greater now than it ever has been with good old analog hard wiring, fieldbus, Ethernet, wireless, and so on. We’ll be coming out of this recession with a lot of work to do. We have the tools, we only need the will.

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