RE: What to use? EtherCAT or Ethernet Powerlink with CANopen protocol

Hi Albert,

You've asked a good question.  But I think it needs to be put into the
correct perspective.  The example below perhaps explains why.

I'm in the middle of a project that uses a solar battery charger, a power
line (generator) battery charger and AGM batteries.  I've had to develop
some custom control modules  because the client feels that off the shelf
PLCs are either too expensive or if from the far east may not be available
next week.  Having full control of their application and hardware is
critically important to them.

The battery charger has CAN J1939 access.  The other modules have CAN bus
on which I've used a simple CANOpen protocol.  The Solar Charger has
Ethernet MODBUS TCP.  To interface I've had to purchase a MODBUS TCP to
MODBUS RTU (RS485) converter.  True, if the main control unit that we used
had Ethernet capabilities the converter wouldn't be needed but to save
costs we used an existing product that has 5 CAN ports, RS485 and I/O.

The real question is whether Ethernet MODBUS TCP is even needed.  Would
MODBUS RTU have been just as effective?  Does a solar battery charging
system really change fast enough that high speed data is required.
Certainly a charger with either CAN or Ethernet would have been more
useful to us.

My point is that for a battery charging system (and many other types of
projects), CAN is more than fast enough and in fact MODBUS RTU at 19200
baud would even work.

We've now seen the introduction of CAN-FD which increases both the data
part bit rate and the number of bytes in a packet.  There are some who
might say Bosch didn't go far enough with a limit of 64 bytes per packet.
In either case, where will it be used that standard CAN would not?

The first versions of Ethernet had the disadvantage of CSMA/CD and
generally suffered past 50% utilization of the bus bandwidth.  The full
duplex Ethernet we use now has the disadvantage of needing a switch and a
much more complicated infrastructure but can run up to Gigabit speeds.

A UDP master/slave or even TCP MODBUS is more than adequate for high speed
networks at the cost of a 32 bit processor and TCP/IP stack code.  IMHO,
every line of code adds to the complexity of a solution.  If you can do it
without the fairly large TCP/IP 7 layer protocol, or the fairly complex
CANOpen with simple CAN transceivers then why not?

I think the high speed large packet size control networks are a minority.

John Dammeyer


"ELS! The Solution"
Automation Artisans Inc.
http://www.autoartisans.com/ELS/
Ph. 1 250 544 4950


> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On
> Behalf Of Albert Saenz
> Sent: Tuesday, December 11, 2012 12:56 AM
> To: [email protected]; 'CANLIST'
> Subject: [CANLIST] What to use? EtherCAT or Ethernet
> Powerlink with CANopen protocol
>
>
> Hi all,
> My first participation!
> I know that perhaps it is not the best forum, but in any case
> I believe many
> of you have the same problem nowadays.
> Despite CAN bus is a nice and powerful field bus (I like very
> much compared
> with any similar industrial bus), we'd need to improve
> notably the speed (1
> Mbit/s is clearly not enough even multiplexing the 8 bytes
> telegrams at
> R-PDO and minimizing all T-PDO). Bandwidth for Hard Real Time
> applications
> were the Tick should be less than 1 ms and massive I/Os and
> Motion Drivers
> should be controlled (typical CNC application) can not be
> limited by the 1
> Mb/s (even using multiple channels: 2 or more CAN buses, as
> our applications
> is using nowadays. 1 for I/Os and 1 o 2 more for control 4 or
> 8 axis with a
> tick of 1 ms). In case we need "multi-channel" (i.e. 2 or
> more independent
> CNCs running at the same platform), CAN bus drastically
> limits and it makes
> no sense in many application.
> My question is (requesting opinions):
> CANopen protocol is supported by EtherCAT (ETG group) and
> Ehernet Powerlink
> (EPGS group) and that simplify migration from CAN bus (or we
> could even
> share both).
> I would like to know Guru's opinion and those are many of you.
> Thanks in advance for your contribution,
>
> Albert Saenz
> Sant Cugat del Valles - Barcelona
>
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