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Rod_Hackney

ethernet/ip for process instrumentation

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We have a system we are putting in with a fair amount of field process instruments. We usually use either 4-20 ma wired or foundation fieldbus to connect to our systems. We had a vendor pitching the idea of using ethernet/ip dedicated network for this since some of the instruments being provided support it. We have traditionally only used ethernet/ip for plc to plc or hmi to plc type communications. We have recently interfaced with some of our VFD's using ethernet/ip and it has worked out fine (did this based on a post and references from my friends at mrplc!) Just wanted to see everyones thoughts on this, thanks in advance for your assistance.

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The big advantage of 4-20mA instruments is cost, selection, distance (kilometers are easily achieved), noise immunity, and the fact that you can run loop powered instruments. The big disadvantages are speed, high cost of analog I/O per point, and the fact that you are limited to one analog transmitter per loop, which drives up the cost of wiring. When you cost out a large project, usually the wiring is where all the cost is overall. The big advantage of FF is being able to localize the processing elements down inside the network. However, this feature is almost never used. The disadvantages are trouble with configuring/installation, high cost of almost everything involved with it, and it is very slow. The whole idea of pushing the processing elements into the network is that you could for instance have the transmitter talking directly to the valve, providing an incredible level of reliability, at least that's the theory. However, I've almost never seen it actually practiced. The big advantages of Ethernet/IP are speed, convenience (everyone is on one network), reliability (continuous diagnostics as well as self healing with rings or RSTP), noise immunity, very simple configuration (most of the time), the potential for configurationless component replacement (not quite there yet), distance (can work anywhere on or off the planet), and very low cost for wiring. The one downside is that having active elements (switches) in the wiring costs a bit more to do.

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Thanks for the response, but I figured it out.

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