Python in Process Control?
benn at cenix-bioscience.com
Fri Oct 1 15:15:51 CEST 2004
Just out of interest - which tecan robot were you interfacing
to - every Tecan robot that I've ever programmed comes with a high level
API (Toolbox, Gemini, Logic, WinWash, Magellen). I would think however
that controlling a tecan robot in the environment that it is typically
being used in (life sciences R+D) is not industrial control (its my job
BTW!). It's not like making milk....
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!) and also bit twiddling is difficult (people who
ask about his on the Python newsgroup are usually shouted at). The
other thing that is a problem for python in this is that it is very
difficult in python to make your your client is aware of all the errors
that you can throw and as you know, when controlling equipment there is
a lot of things that are out of your control (an exception that is
rarely thrown will often not be caught if the programmer never sees it
running and gets lazy).
This is why checked exceptions (as they said in Fantastic Four -
flame on!) in this area are very handy because you are forcing the
non-expert to actively think about these use cases. One thing that
python is good for in this area is comms and threading, the GIL which is
usually a pain in the arse makes multi-threaded IO heavy apps a little
easier to write - although I still spent about 2 days trying to work out
how to make a variable volatile (culminating in understanding the
threading module!). The serial module is good but I think that a model
of input and output streams with listeners/observers would make far more
sense, currently I have to make a polling loop to receive the data, the
reason for this is that a machine may send serial data with being
prompted and this obviously needs to be lexed seperatly than a <I've
done your command here is the response> communication.
Good to see that you didn't use ActiveX (if one more company
_boasts_ that their equipment comes with 'industry standard' ActiveX I
think I'm going to cry)!! Believe it or not I still have to interact
with some equipment using DDE!!!!
This is probably off topic but it's Friday afternoon!!
Senior Automation Engineer
Tel : +49 (0)351 4173 154
e-mail : benn at cenix-bioscience.com
Cenix Website : http://www.cenix-bioscience.com
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