Re: 'best' control network? Devicenet vs Lonworks vs CAN vs Fieldbus vs Ethernet ???

From: Tutors of ESAcademy (esacademy_at_yahoo.com)
Date: 07/30/04 

Date: 30 Jul 2004 01:28:32 -0700

perfb@yahoo.com (perfb) wrote in message news:<775799ec.0407221518.76180fde@posting.google.com>...
> no doubt this is a FAQ oft beat to death, but, assuming
> one wanted to control a network of about 10 i/o modules each
> with maybe 100 i/o digital/analog points, at maybe a 100Hz
> maximum rate (e.g. an automatic industrial processing machine of some kind)
> ...
>
> which control network would be, ahem, for lack of a better word, 'best'?
>
> (i.e. in terms of price/node, support, ease of development, availability
> of second-sources, availability of developers etc.?)
>
> Personally, being somewhat naive and ignorant of the field,
> I would go for ethernet, for sheer availability of tools and
> peripherals. But would I be making a gross faux-pas in doing so?
>
> is ethernet gaining ground as a general-purpose control network
> over e.g. CAN etc.?

To throw in a few more cents (of most likely biased information):

I would not only look at the "best" technology, but also at the
slightly bigger picture:

1.) Do you want to use off-the-shelf components, or develop your own,
or mix both?

If you use ONLY off-the-shelf components, I would make sure that
whatever you pick is supported by at least 2, better 3 big vendors and
that their components can be exchanged and that they have "reasonable"
pricing. Which network technology is actually used then becomes less
relevant.

If you want to develop some or all of the nodes yourself, you should
pick a technology "as open" as possible. One of the reasons we focused
on CANopen is, that it is one of the few protocols that is very
flexible in regards to the functionality you actually implement.
Functionality you don't need you simply don't implement. This allows
for minimal implementations (like www.MicroCANopen.com) greatly
reducing development time and cost, but also helping in keeping
per-node costs down, as smaller microcontrollers can be chosen.

2.) You never mentioned volume and price requirements

If it is a low volume application and the per-node costs are not
terribly important, then again the specific technology is less
important. However, if you have any per-node pricing restraints, you
need to start looking at how to save money.

Here CAN and CANopen are still at the lower end of the scale. A
digital CANopen I/O node can still be built using an 8-bit
microcontroller. Even with all peripheral chips and glue logic needed,
the costs of the hardware components can be below $5 (volume
depending).

Olaf
Tutor at ESAcademy
www.CANopenBook.com

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