power from Profibus , Fieldbus etc

Hi All, I am starting to look at the various busses such as Foundation Fieldbus , Profibus , Can , Devicenet , Control Net , Lon Works , SDS
, Modbus etc.
Can anybody give me links or the name of a good book or article.
My most immediate need is to know how many of these busses can supply power to remote I/O and how much power is available per node.
Thanks
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Tom, the quickest answer is that none of them can. The power on a Devicenet bus (for example) is intended for bus power only - you have to power the remote I/O separately.
There are, however, exceptions to this rule (eg. ASi-bus)...
HTH, Cameron:-)
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Gotta disagree. FF can deliver 20 mA to a half dozen devices on each branch. It can also current limit and be certified IS. The issue isn't the node, it's the voltage drop per branch.
All the books are written by someone with something to sell. The territory is changing as we speak. If it's in print, it's out of date.
Walter.

Devicenet
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Ahh.. yes - I forgot about that. I was thinking of discrete devices only and forgot about loops! :-)
Thanks, Walter.
Cameron:-)
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All the aforementioned require a seperate power line. The exceptiuons are AS-i as you noted and Profibus PA.
AS-i (Actuator Sensor Interface) Profibus PA both modulate the signal on top of a field power supply.
-AS-i is superb for binary sensors and can be made to do analog as well if needed.
-Profibus PA is superb with analog and digital and can be made intrinsically safe as well and is specialsed in plant control. It is a slower but more capable than AS-i. Profibus PA is similar to the standard profibus but uses a modulation scheme that can carry power as well as signal on the same line while offering intrinsic safety and sensor diagnostics and setup. It also can opperate with multiple masters so is a true network as opposed to just a master slave fieldbus.
The bus power and intrinsic safety is only available when the transmision medium is in compliance with IEC 61158-2. (RS 485 can be used but then power is not available)
Of particular interests is the various connection methods which allow very easy wireing without cutting and terminating.
There is also the old 4-20mA based HART system but that is more master-slave multidrop than a network.
Except for Profibus PA both AS-i and HART or more fieldbuses for remote smart I/O.
The CAN standard does not specify the medium so it could be optical, RS485 or whatever. In reality it is mostly RS485.
Interistinly one can obtain profibus DP and FMS to IEC 61158-2 segment couplers.
There is nothing to stop someone from using the CAN or Devicenet protocol on the IEC 61158-2 physical layer so long as it is happy to run at around 31.25kb/sec.
Some data here: http://www.samson.de/pdf_en/l453en.pdf
AS-i uses a 30VDC signal and a sinc squared pulse for both low EMI emision and sensitivity while Profibus PA uses manchester encoding.

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And what is your opinion about the emerging PoE (sp?) [Power over Ethernet]?
Andrey
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wrote:

I think it will do well in the IT area and will also find a niche in industry, particularly data acquisition and in some areas of PLC automation simply becuase it will be cheap and fast while simplifying cableing.
I wasn't aware of it untill you mentioned it. This is an article on it: http://www.commsdesign.com/design_corner/showArticle.jhtml?articleID 100314
There seem to be several versions that either use the spare wires to transmit power or use the data lines to superimpose the signal on 12v, 24v or 48v DC. The standard attempts to reconcile all of these and integrate unpowered hubs by testing them before applying power.
The PoE standard is however designed to opperate via the hub based twisted pair ethernet standards ie 10baseT etc. Thus it physically has a hub and spoke model. This Hube and Spoke model is sometimes incovenient for wireing some types of factory which often do much better in a linear topology. (Admitedly linear topologies are harder to service). Power over Ethernet will also not offer the intrinsic safety (initialy but it is possible) it is also a 4 wire standard not a 2 wire standard. (for what that is worth).
Personaly I like it. It will not be long before someone is offering remote input/output racks. The power available: about 450mA at 36 volts i.e. about 15W will be more than enough for 16 I/O points that have low power proximities, switches and LED based indicator lamps as well as relays and pneumatic solenoids and even small graphics displays based on windows CE.
It will do very well I think.
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Yes, there are a bunch of IT related devices on the market, like wireless access points, voice-over-ip phones, and so on. I have not seen any industrial device with PoE.

Actually I had thought it was a distant future thing in industry, but I changed my mind after attending the "fieldbus war" session at ISA EXPO 2003 back in October.

Hmm.. I am wondering if it is easy to build "PoEred" industrial grade network. Industrial ethernet, besides its emphasis on robust hardware, is based on switches in order to achieve "almost" real-time performance. If I am not mistaken, PoE is back using hubs instead of switches, probably for power consumption reasons.
I like it, too. Ethernet, where its use is appropriate, will make control systems more open and flexible. And PoE is about to fix one of the major Ethernet drawbacks. Sounds promising.
Andrey
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Hi All, given that the consensus is that you cannot generally transfer power over a bus I rechecked the datasheets for a few modules including the FX2n-4AD from Mitsubishi and the 1746SC-NI8U from Spectrum Controls/Allen Bradley.
I believe I was mixing up modules which take power from a backplane with the idea of taking power from the bus.
With the backplanes there seems to be lots of power available eg 5V at 10 amps.
Thanks for the replies
snipped-for-privacy@yahoo.com.au (The Enlightenment) wrote in message

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Tom,
Did you miss it? Foundation Fieldbus is deliberately, from the ground up, designed to transmit power over the bus. It is intended to be used with two wire field instrumentation such as transmitters and valve positioners. If it could not transmit power absolutely no one would use it.
Walter.

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