Python in Process Control?

[Cameron Laird]

Re: Python in Process Control?

In article <mailman.4176.1 096636511.5135. python-list@python.org >,
Neil Benn <benn@cenix-bioscience.com> wrote:

[Richard Brodie]

Re: Python in Process Control?


"Neil Benn" <benn@cenix-bioscience.com> wrote in message
news:mailman.41 76.1096636511.5 135.python-list@python.org ...
[color=blue]
> IMHO, I think that Python is not a suitable piece of software for
> industrial control as it has poor support for bytes (a string shouldn't
> be used to store bytes!)[/color]

That's largely a matter of attitude I think; many would argue that byte
strings shouldn't be used to store text.

[Cameron Laird]

Re: Python in Process Control?

In article <mailman.4176.1 096636511.5135. python-list@python.org >,
Neil Benn <benn@cenix-bioscience.com> wrote:

[Dennis Lee Bieber]

Re: Python in Process Control?

On Fri, 01 Oct 2004 15:08:11 GMT, claird@lairds.u s (Cameron Laird)
declaimed the following in comp.lang.pytho n:
[color=blue]
> consistency of my observations. EVERY time I do process control,
> there are days (sometimes--hold your hats; this is no
> exaggeration--months (!)) of pleading, "No, I really want the
> documentation where you say what it's supposed to do, and what it
> really does", then the the getting-the-right-cables interval of[/color]

Not process control, but my current assignment fits this
roadblock quite well.

I'm stuck with writing a requirements document, software design
document, and then the software, to read a binary stream from device-X.
The only documentation I have for device-X is that I have a 2400baud
RS-232 connection. There is no documentation as to parity, word-length,
stop bits, or handshaking. I'm guessing 8N1 as it is binary data, but
will have to determine handshaking by trial&error.

Furthermore, I don't know how many bytes are in the data stream
per data item. The people who would know if it is fixed or variable
length, or if it even has a delimiter between data items, stonewall with
a "you have no need to know that information".

Scarier thought, device-X is loaded from device-Y which appears
to be using 5-level (+parity?) paper tape! (I'm sure it isn't a 9-pin
tape -- looked like 4pin, sprocket, 2pin). Maybe I'm expected to receive
5-bit data and convert to 8-bit to write as hex...

Just typical government imposed SNAFU... (and people wonder why
so many projects go over budget?)

--[color=blue]
> =============== =============== =============== =============== == <
> wlfraed@ix.netc om.com | Wulfraed Dennis Lee Bieber KD6MOG <
> wulfraed@dm.net | Bestiaria Support Staff <
> =============== =============== =============== =============== == <
> Home Page: <http://www.dm.net/~wulfraed/> <
> Overflow Page: <http://wlfraed.home.ne tcom.com/> <[/color]

[erik.wilsher@gmail.com]

Re: Python in Process Control?

I work with process automation myself, and I belive that writing an OPC
server is *not* a trivial task, even in python. There are some good
books available on this subject, the OPC-foundations home page contains
some good references.

If you want to get started with client code quickly, you could try the
QuickOPC ($) library from OPC-labs (www.opclabs.com). Setting up a
client in python with that library is three lines of code (really!):
------
import win32com.client
import time
s = win32com.client .Dispatch('OPCL abs.EasyDA')

def test(times=1000 0):
v = s.ReadItem('',' Matrikon.OPC.Si mulation', 'Saw-toothed
Waves.Real8','' ,0)
t0 = time.clock()
for i in range(times):
v = s.ReadItem('',' Matrikon.OPC.Si mulation', 'Saw-toothed
Waves.Real8','' ,0)
print time.clock()-t0

test(1000)

[Armin Steinhoff]

Re: Python in Process Control?

Wolfgang Keller wrote:[color=blue]
> Hello,
>
> is it that my know-how to use Google is insufficient or...
>
> ...does really noone use Python for industrial control applications?
>
> At least I didn't manage to find any publicly available modules for such
> things as OPC/fieldbus communication etc...[/color]

I believe you are talking about the OPC version based 0n COM / DCOM ...
but there is in the meantime a SOAP based version called OPC XML defined.

SOAP and XML support are available for Python ... who will implement
OPC XML for Python ??

Best Regards

Armin Steinhoff

http://www.steinhoff-automation.com

[color=blue]
>
> TIA,
>
> best regards,
>
> Wolfgang Keller[/color]

[Carlos Ribeiro]

Re: Python in Process Control?

On Fri, 01 Oct 2004 09:14:40 -0400, Peter L Hansen <peter@engcorp. com> wrote:[color=blue]
> Wolfgang Keller wrote:[color=green]
> > There seem to be some Python bits out there, for example MatPLC and
> > Lintouch use Python and some commercial products as well (PyDACHS), but
> > unfortunately there doesn't seem to be a more or less consistent library
> > for industrial automation or a coordinated effort to build up one.[/color]
>
> What, in your opinion, would it take to start one? I'm able to
> offer the use of a server to host a web site, and would be happy
> to register a domain name or something, but those are the easy
> bits. Some kind of core group to get it off the group is likely
> more important than a name, though sometimes threads in this
> group might lead one to suspect otherwise. ;-)[/color]

I did work on software development for remote monitoring devices in
the mid 90's, using C and ASM. I worked with serial communication, and
in *all* cases, I had to implement some "brad-new" proprietary
protocol, or emulate a twenty-year-old one that was poorly documented,
if documented at all. I sincerely don't understand why is this market
so reluctant to progress. All parties involved are *so* reluctant to
share information as to make real progress impossible. It may be
because of their business model, where they expect to make some money
out of "services" -- customization, selling drivers and development
kits -- but even so, the industry as a whole seems to be stuck in the
past.

I now have a related interest that would probably benefit HUGELY from
this effort, and in fact, could help to "bootstrap" it: residential
automation. Yes, I know that the protocols are different, and the
needs are different, but the situation is pretty much the same as for
both fields: too much closed solutions, bad documentation, and people
still stuck at ten-years old technology. A good forum could bolster
the discussion, and the development, of new technology for residential
automation, which has the kind of mass appeal that can make things
scale up better.


--
Carlos Ribeiro
Consultoria em Projetos
blog: http://rascunhosrotos.blogspot.com
blog: http://pythonnotes.blogspot.com
mail: carribeiro@gmai l.com
mail: carribeiro@yaho o.com

[Phil Schmidt]

Re: Python in Process Control?

Wolfgang Keller <wolfgang.kelle r.nospam@gmx.de > wrote in message

<snip>
[color=blue]
> ...does really noone use Python for industrial control applications?[/color]



This isn't quite industrial control, but the principle is similar:

I used Python, along with Mark Hammond's win32 extensions and
pyserial, plus a Dearborn Group VSIC2 interface to create a GM (as in
General Motors) Class 2 bus tool. It was (for me) a general-purpose
tool, allowing me to get real-time bus traces, as well as simulate
portions of vehicle communications for testing, extract diagnostic
codes, log bus traces to disk, and etc. The program used an event loop
on a virtual internal bus, which allowed me to quickly and easily
create new tool applets (Tkinter gui's) and just plug them into that
virtual bus. I had a couple dozen applets that I created and used.

I started the project unsure if Python was up to the task, but I was
pleasantly surprised in the end. I polled the serial port to look for
messages from the VSIC2 box, and I was able to poll it at about 9000
scans per second in trace mode, and about 5000 scans per second with
all of my tools running, all on a circa-2002 Dell laptop. On a
10.4Kbaud vehicle bus, this was more than adequate performance.

Bottom line: Depending on the specific needs I think Python could
handle some process control tasks.

[Andrea Griffini]

Re: Python in Process Control?

On Sat, 02 Oct 2004 11:50:25 +0200, Armin Steinhoff
<a-steinhoff@web.d e> wrote:
[color=blue][color=green]
>> ...does really noone use Python for industrial control applications?[/color][/color]

I implemented the control software for an automated
tangential sewing machine in python (it's a 4 axis
control). The low-level part for axis control runs
on custom hardware, but all the high-level part
including path computation with dynamics constraint
has been coded for a PC in pure python that happened
to be fast enough. The program uses a serial port
and a parallel port to communicate with the low-level
part of the NC, and the user interface has been
coded to work fullscreen using pygame.

It was just a prototype I coded that way basically to
test python, but I was surprised with the results
that seem to me more than adequate. In my case I had
just soft realtime constraint (the low-level part is
able to stop and restart gracefully in the event of
buffering underflow in the axis control data feed)
but I didn't observe any real problem (the axis are
controlled with dt = 1ms).

Andrea

[Wolfgang Keller]

Re: Python in Process Control?

Hello,
[color=blue]
> I believe you are talking about the OPC version based 0n COM / DCOM ...
> but there is in the meantime a SOAP based version called OPC XML defined.[/color]

You mean XML-DA, I guess?

Indeed, the standardisation of SOAP as a protocol for process control makes
Python an even more interesting candidate for such applications. Because
with Python, implementing SOAP clients and server should be ridiculously
more efficient concerning development effort compared to most lower-level
languages and ridiculously more efficient concerning runtime resource
requirements compared to Java.

Regards,

Wolfgang Keller

[Armin Steinhoff]

Re: Python in Process Control?

Wolfgang Keller wrote:[color=blue]
> Am Fri, 01 Oct 2004 09:14:40 -0400 schrieb Peter L Hansen:
>
>[color=green]
>>Wolfgang Keller wrote:
>>[color=darkred]
>>>There seem to be some Python bits out there, for example MatPLC and
>>>Lintouch use Python and some commercial products as well (PyDACHS), but
>>>unfortunatel y there doesn't seem to be a more or less consistent library
>>>for industrial automation or a coordinated effort to build up one.[/color]
>>
>>What, in your opinion, would it take to start one?[/color]
>
>
> Work? >:->
>
> A SIG would already be more than nothing, then start to set up a site with
> a few links to things that are already available (whether free or
> commercial), then start to collect things which are open-source and/or
> free, then start to improve them and complete what's missing andsoon...
>
> I have a dream :-): A Python library for industrial automation that is as
> complete and well-documented as, for example, twisted for TCP/IP
> communication.
>
> You need an OPC server/client? - Import a module, instantiate a class and
> there you go.
>
> You need to talk <insert_your_fa vorite_fieldbus _here>? Same procedure...[/color]

What do you need ?

Profibus-DP ? a GSD based Configurator for Profibus-DP?
Interbus G4 ?
plain CAN ?
CANopen ?
EtherCAT (in development) ?

It's available for QNX6 !
[color=blue]
> Ah yes, and obviously have Python ported to all those RTOSes and embedded
> controllers (PowerPC, StrongArm/XScale, MIPS, SH)...[/color]

QNX6 works with these processors :)

Regards

Armin Steinhoff

http://www.steinhoff-automation.com

[Wolfgang Keller]

Re: Python in Process Control?

Hello,
[color=blue]
> What do you need ?[/color]
[color=blue]
> plain CAN ?
> CANopen ?[/color]

That's already useful.

MVB and WTB are THE standards in the world were I live. :-)

FIP and LON are commonly used as well. Modbus sometimes.
[color=blue]
> It's available for QNX6 ![/color]
[color=blue][color=green]
>> Ah yes, and obviously have Python ported to all those RTOSes and embedded
>> controllers (PowerPC, StrongArm/XScale, MIPS, SH)...[/color]
>
> QNX6 works with these processors :)[/color]

Ah, while you're at it, how about making PyQNX stackless? Could be quite
usefull for communication and statemachines, I guess. :-)

*duck*

Regards,

Wolfgang Keller