Articles to Read

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One of my pet peeves is referring to “wireless” as one monolithic thing.  Peter Welander does a good job of breaking down the monolith into sensible pieces in the Control Engineering article “Topologies for Wireless Instrumentation.”  Wireless for PROFIBUS and PROFINET is in the category of “wireless fieldbus backhaul” in the article.  We are working with Fieldbus Foundation and HART Communication Foundation on a common wireless device approach, too.

Automation World has an article “Ethernet Takes the Field” that provides an overview of Industrial Ethernet.  The article has comments from genuine experts like John Rinaldi of Real Time Automation, several users, me (I’ve humbly excluded myself from the “expert” category), and some clueless guy from Rockwell who thinks Ethernet/IP is the only non-corrupting Industrial Ethernet.  (Every time I see some variation of “corrupt” I have to count to ten before reacting.  You do know that the IP in Ethernet/IP does not stand for “Internet Protocol,” but “Industrial Protocol,” right?)  Important points from the article:

  > Ethernet is rugged enough

  > Ethernet is not yet applicable to on-off devices

  > There are tools from the office world that help

  > Let performance needed dictate which Industrial Ethernet to pick

  > The lack of a single standard may inhibit adoption (or not)

My opinion [you knew I would have an opinion, didn’t you] is “absolutely” for the first three, even agreeing with a Rockwell guy on the tool issue.  With Ethernet switches in a PROFINET system, users can choose the standard IT tools or with several switch vendors they can choose to treat the switch like a PROFINET IO device.  This lets them bring information to their PLC or HMI and react to any problems detected.  On the performance dictating the choice, I am of a different opinion.  I believe you should choose the network that meets all your current and future needs, including performance (of course), but also the ability to span discrete, process, and motion devices, to integrate safety, to easily provide peer-to-peer integration, to use wired or wireless, etc.  This way the user only has to buy and learn one set of tools.  On the final point, I believe competition is a good thing that makes all participants strive to improve.

ARC reported on the CIP Forum Japan 2007.  Here’s a comparison between the points from the keynote at the forum with respect to PI (PROFIBUS and PROFINET International):

  1. “ODVA is a truly open organization…”  Ditto for PI with over 500 specialists in over 50 Working Groups advancing the PROFIBUS and PROFINET open standards.

  2. CIP is based on the producer-consumer model.  Hmm, I thought DeviceNet was Master/Slave.  Try this Google search and you’ll get a lot of pages that seem to support that idea.  Not there’s anything wrong with Master/Slave; that’s the way PROFIBUS works, although PROFINET is Provider/Consumer.  Master/Slave works by having the master communicate sequentially to each slave in a round-robin fashion.  Provider/Consumer allows any required communication to occur between any provider and any consumer at any time.

  3. “CompoNet debuts as Sensor-Actuator Network.”  When there are CompoNet products available, they will compete with the well-established AS-interface bus.  One of the downsides of CompoNet is the introduction of a new set of connector types.

  4. “More than 1,000 vendor IDs have been applied for and issued for the family of CIP Networks.”  PROFIBUS has more than 2,800 devices available with PROFINET adding hundreds more.

  5. Schneider Electric joined ODVA.  We don’t have a comparable category to ODVA’s “principal member,” but Schneider Electric is a member of PTO.  (Even Rockwell is a member of PI!)

Design News has an article on Ethernet and motion control: “Motion Is Moving to Ethernet.”  The author mentions all the leading contenders and spends a fair amount of time on Ethernet/IP.  He even talks about there being no shipping products from them yet.  PROFINET has had shipping products for some years now.  The author also accuses those of us who represent the various Industrial Ethernet motion control technologies of engaging in “specsmanship.”  I don’t look at it as specsmanship, but I will tell you why I think PROFINET’s approach is superior to Ethernet/IP’s.  Ethernet/IP is going to rely on synchronizing the device clocks.  Synchronizing the clocks is not the same as synchronizing the motion axes!  PROFINET relies on bandwidth reservation to ensure that the motion control information gets through, regardless of any other traffic on the network.  Attend one of our PROFINET one-day training events in 2008 for more detail or view our archived PROFINET webinar for a really short introduction.

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