Profibus Protocol vs. others?

Profibus is okay, but not widespread like modbus.

How many PLCs or OITs speak modbus? Answer - almost ALL.

How many speak Profibus? __________________
 
For your information, Siemens is the largest PLC supplier in the world and all of their PLCs speak Profibus. Profibus is the best supported protocol
in the factory automation and material handling applications area. It is supported on all of Siemens product line including variable speed drives, high voltage switchgear, and Siemens' HVAC business formerly Staefa and Landis & Gyr, one of the world's largest.

Maybe the reason we don't hear much about Profibus on this list is that it is so well supported by Profibus International www.profibus.com and hundreds of major suppliers. Profibus has been stabilized by being a German national standard since 1991.

Modbus.org only recently was staffed in order to support Modbus protocols that tended to evolved over the years since 1972 when it was created.

Dick Caro
============================================
Richard H. Caro, CEO
CMC Associates
2 Beth Circle, Acton, MA 01720
Tel: +1.978.635.9449 Mobile: +1.978.764.4728
Fax: +1.978.246.1270
E-mail: [email protected]
Web: http://www.CMC.us
============================================
 
S

ScienceOfficer

Dick---
I don't even have a horse in this race, but I get annoyed in my own market
by agents overstating the Profibus case, and I have to jump in here.
Siemens is a fine company, and Profibus is a fine network, but the question
was about features that would recommend Profibus over Modbus, not marketing
hype.

Yes, Siemens products speak Profibus. They speak Profibus DP, or Profibus
PA, or Profibus FMS, or Profibus CAN, or one of the other flavors of
Profibus including the proprietary SINEC versions that make up a huge
amount of the installed base. In other words, Siemens developed
technologies and marketing strategies just as everyone else did over the
last twenty years. It's disingenuous to lump them all together as one
"Profibus" and claim it's the "best supported protocol in the world." It
might be more accurate to say that networks now branded as "Profibus" have
been installed in a lot of places over the last twenty years. There are
also a few flavors of Modbus, but I've rarely detected a Modbus advocate
pretending they were all one.

It might be that we don't hear about Profibus on this list for the same
reason we don't hear about Seriplex or SDS or Data Highway II--- no one on
this list is using it.

And you'll have to forgive me if I yawn when told that Germany at some
point adopted a German company's product as a standard. I'm half-Deutsch,
speak the language decently well, and have the bruises from business
interaction with German clients. If the BMW Isetta had been more
successful, we'd have a German standard for three-wheeled cars!

In fact, Profibus is a minor factor in the North American market, according
to ARC, and Modbus has to be acknowledged as a major factor with a huge
installed base and an interesting fan base ranging from hobby to SCADA.

I compete against Modbus, too, but I tend to do that with technical and
support arguments. In my market, Modbus has some decent support, but
Profibus problems have no help, according to my integrators and machine
builders.

Hope this helps!

Larry Lawver
Rexel / Central Florida
 
T
And, I might add, in many thousands of devices not produced by Siemens! The great thing about Profibus, in my opinion (and having been involved in both Profibus and DeviceNet for many years) is its extreme simplicity of application - it's really just a fast memory transfer between slaves and master, working like clockwork. And because slave devices tend to be based on the same chipset (SPC3 or derivative), they all work pretty much alike. We've been shipping Profibus products for years, and the product support load is almost non-existent. Things (usually) just work.

DeviceNet does the job, but is short of bandwidth for bigger machines. It would be interesting to know how many wholly AB systems use it in preference to DH+, and I suspect not all that many.

ASI then provides a good lower level capability to both Profibus and DeviceNet (or anything else).

I'm always amused by Groupe Schneider's evident glee at finding that having backed perhaps the wrong fieldbus contenders a few years ago, they now (in effect) own the de facto Ethernet standard for automation! I see a very seductive network technology for the future being traditional RS485 Modbus subnets around a machine, linking into an Modbus/TCP Ethernet gateway between machines and into supervisors, ERP, and panels. This to my mind gives the best of all worlds for distributed control, though I suspect not up to the job for a true distributed fast I/O backplane, for which Profibus or DN are better suited (because of their design around a precise cyclic interchange).

Tim Linnell (Eurotherm)
 
D

Donald Pittendrigh

Hi All Perhaps the reason why we don’t hear much about it is that it is so trouble free there is not much to discuss. I hear all the modbus queries and I am thankful to not be in that particular game. I have not installed any I/O on new machines in the last 5 or 6 years that were not Profibus, even the local I/O is profi to standardize on drawings and hardware and panel construction and it is a recipe that really works for us. We have scales, encoders, masterdrives, yaskawa drives, inclinometers, remote control operator stations and countless other devices running on several cross vendor platforms without any real difficulty.

Oh I did install some ASi I/O a few years back so the point above is not quite true, but these failed so dismally to perform in an MCC panel that they were taken out and replaced with profi stuff.

Regards Donald P
 
D

Donald Pittendrigh

Hi Dick and Others

Perhaps there is no race? But if there were, I certainly know which one I would have my money on for speed, the purple one.

> I don't even have a horse in this race, but I get annoyed in my own
market
> by agents overstating the Profibus case, and I have to jump in here.
> Siemens is a fine company, and Profibus is a fine network, but the
> question
> was about features that would recommend Profibus over Modbus, not
> marketing
> hype.

The statement made below about no-one using Profibus will now be ignored by all torch carrying members of the Profibus Organization and all other Profibus fans are not allowed to respond. Moderators please attend to this otherwise you are going to spend the rest of Easter moderating "Profibus Protocol vs Others" emails!!!!

> It might be that we don't hear about Profibus on this list for the
same
> reason we don't hear about Seriplex or SDS or Data Highway II--- no
one
> on
> this list is using it.

We will forgive you if you yawn, it is maybe possible you were asleep, when the (Profi)bus left the station without you?

> And you'll have to forgive me if I yawn when told that Germany at some
> point adopted a German company's product as a standard. I'm
half-Deutsch,
> speak the language decently well, and have the bruises from business
> interaction with German clients. If the BMW Isetta had been more
> successful, we'd have a German standard for three-wheeled cars!

I doubt the following statement is true and a brief scan of the members of the Profibus users group ought to put it in perspective, I think you
may even find that the greater percentage of manufacturers listed are North American, but I am not sure, I didn’t count.

> In fact, Profibus is a minor factor in the North American market,
> according
> to ARC, and Modbus has to be acknowledged as a major factor with a
huge
> installed base and an interesting fan base ranging from hobby to
SCADA.

I am having trouble interpreting the meaning of compete in the statement below, especially in the light of the opening statement about horses and
races. I didn't know there was a competition and I bet if there was a survey conducted on this list most users will be using the most appropriate bus for the PLC they select, using Modbus on a siemens is dumb, I know as I have done it, not because I wanted to. Now if you want
to talk about CPU competitions and passions, that will be different.

> I compete against Modbus, too, but I tend to do that with technical
and
> support arguments. In my market, Modbus has some decent support, but
> Profibus problems have no help, according to my integrators and
machine
> builders.

I am not sure what Dick's "market" is and what qualifies as "decent support" or "help". I have had Profibus problems with a link between Yaskawa drives and Siemens PLC's, once, gave me a lot of trouble and took a whole night to fix. I found the problem eventually, the Yaskawa effectively removes the terminating resistor when the power is removed from the bus, and I had the last drive switched off. I solved the problem with a few inches of cable and a spare Profibus plug. All other busses have been plug in and switch on (I refuse to use the popular acronym, I differentiate between work and play) and although I have found some problems with most busses I have worked on, they have all been cabling and plug related, not one single on has ever been due to malfunction of the PLC or software or bus interface cards, what could be simpler, I have yet to find a bus system that tells you what the problem with the slaves is when the cable is broken, and my Profibus tells me, "slave not available" when that happens, so I don't really know about these problems and this help mentioned above.

Regards
Donald P
 
M

Michael Griffin

Recently, under this subject two theories were advanced to explain the question of why "Profibus is seldom discussed on this list". One suggestion was that the reason why we hear so little about Profibus is that relatively few problems are encountered. Another suggestion was that the reason was that it was seldom used. No facts were offered to support either of these suggestions.

It occured to me that it would be relatively easy to review the fundamental assumptions of both of these premises by reviewing the mail from this list. The following is what I have discovered:

In the mail dating from the beginning of 2003 up to the 2nd of May 2003, there were a total of 6871 messages. By using the "search" function in my e-mail program, I was able to automatically count up how many messages had the names of various networks in the subject lines. The results are tabulated as follows:

Total messages / Originating messages / Replies a) Modbus (584 / 144 / 440), b) Profibus (116 / 24 / 92), c) Foundation Fieldbus (22 / 5 / 17), d) Controlnet (18 / 5 / 13), e) Devicenet (8 / 3 / 5), f) ASI (6 / 2 / 4)

Total messages for 2003 to date on all subjects: 6871. An originating message was one which begun a discussion. A reply was one beginning with "Re:".

It is worth noting that "Profibus" was the subject of 116 messages in total (including 24 originating messages). Profibus was the subject of more than twice as many messages as Foundation Fieldbus, Controlnet, Devicenet, and ASI *combined*. Approximately 1.7% of all the messages so far this year had "Profibus" in the subject line. In comparison, Devicenet was the subject of only 0.1% of the messages, and Controlnet 0.25%. However, Modbus appeared in 584 messages, or 8.5% of total messages.

In other words, the premise that Profibus is seldom discussed relative to other buses is not supported by the facts. Given these facts, the explanations for why "Profibus is seldom discussed" can be dismissed. Profibus is in fact the subject of a significant number of discussions.

Two types of buses, Modbus and Profibus where the subject of the bulk of the discussion (more than 10% of all messages). To look further into this, I decided to try to classify the "originating" messages according to what the major questions were in the body of the message. The classifications are subjective, but still useful.

Review of Profibus (24) and Modbus (144) originating messages:

a) Search for a product: Profibus - 5, Modbus - 12. These were questions about where to find a compatible device or software. b) Search for gateway or signal converter: Profibus - 6, Modbus - 16. These were questions specifically about where to find communications gateways, modems, infra-red links, etc. c) How to install/apply: Profibus - 10, Modbus - 40. These were general questions on wiring, installation, configuration, and troubleshooting. d) General technology: Profibus - 3, Modbus - 11. These were general questions on how the bus worked, which one was better, etc.

The following apply to Modbus messages only : e) Protocol, command, or register mapping: Modbus - 36. These were questions on proper register mapping, commands, and protocol details. Some of these questions may have been asked by people who were writing their own drivers, but did not state the reason why they were asking for information.

f) How to write own driver: Modbus - 29. These were questions specifically from people who stated they were attempting to write their own drivers.

--

************************
Michael Griffin
London, Ont. Canada
************************
 
D

Donald Pittendrigh

Bravo Michael

Someone who loves to get at the truth whatever!!!

Please revise your assessment for the Profibus figures, taking into account the GSD keyword, as I know the writing and modification of GSD files has been discussed and would not necessarily include reference to Profibus in the subject line. I did a quick search and there were 62 references with only 32 containing Profibus in subject.

As far as Siemens goes, there are also many references to Sinec L2-DP which are about Profibus but won't necessarily contain the Profi keyword.

If you have your study results in sortable form, perhaps you could also tell us how many of the queries on each bus were replied to and how many were left out in the cold.

One fact did impress itself upon me when I got to the end of your report, and that is that Profibus users don’t seem to need to write their own drivers, that I think is an extremely convincing motivation to avoid the competitors.

Do also take note that the initial observation as to Profibus not being heard of due to its trouble free nature was probably made by me, it was intended to be a lighthearted statement, not scientific analysis.

Thanks for the interesting info.

Donald P
 
M

Michael Griffin

On May 4, 2003 15:32, Donald Pittendrigh wrote:
<clip>
> Bravo Michael
> Someone who loves to get at the truth whatever!!!
>
> Please revise your assessment for the Profibus figures, taking into
> account the GSD keyword, as I know the writing and modification of GSD
> files has been discussed and would not necessarily include reference to
> Profibus in the subject line. I did a quick search and there were 62
> references with only 32 containing Profibus in subject.
>
> As far as Siemens goes, there are also many references to Sinec L2-DP
> which are about Profibus but won't necessarily contain the Profi
> keyword.

I used as a sample only the Automation messages from the beginning of this year until now. I wanted to keep the amount of data I was examining to a managable amount. This was not an exhaustive survey. If I look at the data for all of 2002, I find a total of 353 matches out of 20092 messages. This is 1.8%, which is approximately the same proportion as in the sample period I
originally selected. In other words, there is approximately one Profibus message for each active day of the automation list. Therefore, it is not reasonable to say that Profibus is seldom discussed here (this is the point I wanted to make).

Refining the search to find additional matches adds little to this. If I search the original sample period, using "GSD" adds another 7, and "Sinec L2" adds 6 (I searched the entire message for these references, not just the subject line). In other words, most people seem to use the phrase "Profibus". There are doubtless other phrases I could search for, such as references to specific communications cards. However, this would have made it difficult to
compare to other buses, as I would have had to come up with similar references for them. I think that at this point there is little to be gained
by searching out a few more matches.

If I search for "Profibus" anywhere within the message, I find at total of 296 messages which match. However, a brief examination of them shows that many of the additional messages mention Profibus, but are not really about it. I
originally decided to just look for messages which had "Profibus" in the subject line, as the message would likely to be quite clearly about
"Profibus".

> If you have your study results in sortable form, perhaps you could also
> tell us how many of the queries on each bus were replied to and how many
> were left out in the cold.

All I did was to use my e-mail client program's search function. It tells me how many messages were processed, and how many matches were found. This takes only a few seconds and is what I used to come up with the basic statistics. The classification of "Modbus" and "Profibus" message contents required actually reading them and applying some judgement.

However, you raised an interesting question from the point of view of how many replies are generated. For Profibus, the following is a list of originating message subjects, together with the number of replies for each in brackets
following. There were also 3 replies for which there was no original message (possibly either a reply to a message outside of my sample period, or I didn't receive the original message).

APPS: HART/PROFIBUS gate (2)
COMM: 1771 Adapter with PROFIBUS interface (2)
COMM: Connect S5-95U plc to a profibus network (4)
COMM: material/type of profibus-DP (3)
COMM: Modbus / Profibus FMS (1)
COMM: PLC as Profibus Master or Slave? (6)
COMM: profibus-DP (7)
COMM: Profibus DP Connection (1)
COMM: Profibus/MPI addressing (9)
COMM: Profibus Protocol vs. others? (9)
COMM: Profibus Radio Bridges (0)
COMM: Program for Profibus DP (3)
COMM: Quantum / Profibus FMS (2)
INFO: Intrinsically Safe Profibus Barcode Scanners (0)
NET: Profibus-PA VME Interface (5)
NET: profibus to fiber converter (6)
NET: Profibus Wireless link (5)
PC: Intouch DDE server to profibus FDL? (2)
PC: suppliers for PCI based profibus cards (5)
PLCS: Choosing a network (MPI,PROFIBUS,ethernet) (5)
PLCS: COMM: S7 Profibus Comms (0)
PLCS: Profibus network with a Siemens 315-2DP and C7. (2)
PLCS: PROFIBUS REPEATERS (4)
PROC: Profibus DP intelligent motor starter (4)

Some additional interesting statistics. Number of Profibus replies from one individual:
Donald Pittendrigh: 14
Daniel Chartier: 6
All others - 3 or less replies each.

> One fact did impress itself upon me when I got to the end of your
> report, and that is that Profibus users don't seem to need to write
> their own drivers, that I think is an extremely convincing motivation to
> avoid the competitors.

I believe you are referring to Modbus. I didn't perform any detailed examination of the messages for anything other than Modbus and Profibus. I
would look at the matter slightly differently than you. Many people *can* write their own Modbus ASCII or RTU drivers. Very few are in a position to do so for Profibus. The amount of hardware required is also quite different. Modbus ASCII or RTU cannot be directly compared to Profibus.


> Do also take note that the initial observation as to Profibus not being
> heard of due to its trouble free nature was probably made by me, it was
> intended to be a lighthearted statement, not scientific analysis.
<clip>

I noticed that a conversation was taking place which seemed to take as its premise that Profibus was seldom discussed. This "fact" was simply tossed into the discussion (by someone else) and accepted without question by everyone who then tried to find reasons why this "fact" proved their position. A few seconds of elementary checking showed there was no basis for it. Some rather pointless discussions here follow a similar course.

P.S. - Question - Which subject was more commonly discussed on this list this year - "Profibus" or "Linux"?

Answer - "Profibus" is the subject of 119 messages, and "Linux" only 73. "Profibus" appears in the body of 296 messages, while "Linux" appears in the body of 276. In other words, Profibus was more commonly discussed on this
list than Linux. Would you have guessed this? The amount of heat generated is not necessarily proportional to the frequency of discussion.

************************
Michael Griffin
London, Ont. Canada
************************
 
F

Frank Iwanitz (Softing AG)

Hello,

I would like to answer on some of the statements
made in this message.
see below.

> It
> might be more accurate to say that networks now branded as "Profibus" have
> been installed in a lot of places over the last twenty years.

I totaly aggree.

> It might be that we don't hear about Profibus on this list for the same
> reason we don't hear about Seriplex or SDS or Data Highway II--- no one on
> this list is using it.

Maybe lot of people are using, but do not have
problems? ;-(


> And you'll have to forgive me if I yawn when told that Germany at some
> point adopted a German company's product as a standard.

This is wrong. PROFIBUS FMS has been a result
of a joint research project in Germany at the
end of the 80 ies. Yes, Siemens has played an
important role, but there have been a lot more
companies.

PROFIBUS DP (V0,V1,V2)is based on a proposal(s) from Siemens, but again the spec has been defined by a number of companies.

At least PROFIBUS PA, this would not exist if the
ISP had not been terminated by some well known
companies ...

> In fact, Profibus is a minor factor in the North American market, according
> to ARC, and Modbus has to be acknowledged as a major factor with a huge
> installed base and an interesting fan base ranging from hobby to SCADA.

To be honest I do not believe much in the
"research" studies of any "analysts" either
in the automation market nor in the stock market.

There are a number of companies (US based) which
sell PROFIBUS and obviously make some money.

> I compete against Modbus, too, but I tend to do that with technical and
> support arguments. In my market, Modbus has some decent support, but
> Profibus problems have no help, according to my integrators and machine
> builders.

Sorry, which problems do not have help?

Thanks.

Regards,

Frank Iwanitz
 
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