[triangle-zpug] Linking DAQs to Data Turbine

Lee Nelson lee_nelson at ncsu.edu
Wed Jan 23 23:16:16 UTC 2008


I'm sorry I wasn't more prepared last night but here is the problem I was
trying to present.  For anybody who wasn't there, I am new to Python but I
am trying to create a Python link between two programs.  I have been
investigating, working on this, and trying to learn Python for about six
months.  While the problem seems relatively simple, I'm currently
overwhelmed with all of the options and everything I'm trying to learn.  I'm
hoping this group might provide me with some direction.  

 

All of the files referenced in this email can be accessed by downloading
this file: http://www.cfl.ncsu.edu/temp/Python_Group_Attachements.zip. 

 

As a quick summary, I want use Python to access data from a program called
StrainSmart via a COM interface, do a small amount of string manipulation,
and stream the data in an ASCII format over the network to a program called
Data Turbine.  StrainSmart is a program from Vishay Micromeasurements in
Wendell, NC and it is designed to control their data acquisition hardware.
Data Turbine is an open source java program that synchronizes and archives
data and video from multiple sources.  Once the data and video is in Data
Turbine, there is a very powerful front end called RDV or "Real-Time Data
Viewer" for viewing and plotting live and archived data over the network
(http://it.nees.org/software/rdv/index.php).  The details of each program
and it's interface is below:

 

StrainSmart:

 

.         StrainSmart software is used to control data acquisition hardware
from Vishay Micromeasurements, a company which is located in Wendell, NC. 

 

.         Vishay provides a number of methods for accessing data from
StrainSmart.  The most appealing method to me is their "High Level OLE
Automation Server" which is documented here:
http://www.vishay.com/company/brands/measurements-group/Software/Interfac/hi
_level.htm.  I chose this interface over the lower level interfaces because
it doesn't interfere with the operation of StrainSmart and it outputs fully
reduced data rather than A/D counts.  I have been able to access the
properties and methods of the high level interface with Python (using the
win32com module).

 

.         One of Vishay's Applications Engineers wrote the attached VBA
example of how to access this interface (Reduced Data.zip).  The VBA example
has a graphical interface and streams data from StrainSmart into an excel
worksheet while StrainSmart is recording.  I was able to sit down with the
Applications Engineer who wrote this program and have him explain how it
works.  

 

Data Turbine:

 

.         Data Turbine is an open source java program that is supported by
NEESit: http://it.nees.org/software/dataturbine/index.php.  NEES is the NSF
sponsored "Network for Earthquake Engineering Simulation" and it consists of
about 15 large structural testing facilities.  NEESit is a part of NEES that
develops and supports IT infrastructure and software for these labs.  My lab
at NC State (www.cfl.ncsu.edu) is not a part of NEES but I am very
interested in using the same open source software.  I recently spent a week
at the UCSD Supercomputing Center learning how to use everything.  In order
to implement the software, I first have to develop software links to our
specific hardware.  These data acquisition systems are the first and most
important piece of equipment that I want to link into Data Turbine.  I
already have network cameras which send video streams directly into
DataTurbine.  

 

.         NEESit provides a LabView program called NEESdaq
(http://it.nees.org/software/daq/index.php) which is capable of getting data
from National Instruments hardware and this is what most of the NEES labs
use.  My lab has invested heavily in Vishay hardware and there is no desire
to purchase high channel count National Instruments systems.

 

.         Data Turbine is also known as RBNB or "Ring Buffered Network Bus"
and it was originally written by a company called Creare
(http://outlet.creare.com/rbnb/index.html).  It has a Java API which is
documented on the Creare website:
http://outlet.creare.com/rbnb/WP/V2.0/Documentation/Java/com/rbnb/sapi/packa
ge-summary.html.

 

.         To simplify the interface with Data Turbine, NEESit used the Java
API to create an intermediate program called DaqToRbnb.   DaqToRbnb accepts
simple ASCII commands and data over TCP and it is documented in the attached
file (TR-2004-35.pdf).  

 

.         After several months of unsuccessfully trying to write this
program by myself in Python, I contacted NEESit and they sent me the code
for the attached program called fake_daq (fake_daq.zip).  Fake_daq is
written in C and it basically sends sine-wave data to Data Turbine through
DaqToRbnb.  The idea is that somebody could replace the sine-wave generator
with their DAQ code and use this program.  

 

So with all of this information, these are some of the options I have come
up with for proceeding with this project:

 

.         Interface directly with the Data Turbine Java API.  I know very
little about Java and this seems like a very difficult option compared to
using DaqToRbnb.  It could be possible using something like Jython???  The
data acquisition and the Data Turbine server would always be separate
computers so there would have to be some network programming involved.  To
me it seems much easier to use DaqToRBNB which is already written and
extensively tested.  I initially looked at doing this whole program in Java
but I abandoned the idea when I tried to access the StrainSmart COM
interface using one of the open source Java to COM bridges.  The COM
interface is why I initially switched to Python.

 

.         Try to adapt the LabView code of NEESDaq to my Vishay hardware.  I
think there may even be some VI's for executing python code in LabView.
I've done a lot with LabView in the past but I would have to learn a lot
more to work with NEESDaq.  I enjoy real coding and if I'm going to spend
time learning a programming language, I would rather learn Python because I
probably won't have a license for LabView if I ever leave the University.

 

.         Write my own Python Code from scratch - I have been working on
this but I am currently stuck.  A professor in my department's Computer
Aided Engineering group suggested that I look into some packet sniffing
software to look at the network communication between my program and
DaqToRBNB so that I can compare this to some successful communication
between NEESDaq or fake_daq and DaqToRBNB.  This is what I'm presently
working on with my code.

 

.         Try to convert the fake_daq C code to Python - essentially try to
copy the design of fake_daq.  The code in fake_daq is much more advanced and
robust than what I was trying to write by myself in Python.

 

.         Try to access the COM interface from within C - I've read that
this is possible.

 

.         Try to compile the C program in C++ where I've read it's easier to
access the COM interface.

 

.         Use SWIG generate an interface and use the C functions from
fake_daq in Python.

 

.         Use C-Types ???

 

.         Try to embed my Python function to get data from the COM interface
in fake_daq.

 

 

I'm sure there are also many other options.  Thus far I am very excited
about learning Python and am hoping to use it on several other projects, so
I would like to stay with a Python solution if at all possible.    Please
let me know if you have any suggestions or advice and thanks in advance for
your help.  

 

For what it's worth I attached the code that I am working on.  I basically
just set up two sockets, a control socket and a data socket.  When I start
both programs, I start receiving commands from DaqToRbnb and my Python code
responds to those commands (currently with predetermined arbitrary responses
- I will eventually have to work with the COM interface to extract this
information from StrainSmart and send it to DaqToRBNB - I am currently
working on this in a separate program).  My program works fine until it asks
me to start streaming data on the data socket, then it crashes (I don't
recall the exact message . I will have to get all of the programs up and
running to recreate the error).  In fake_daq this is where they start a
separate thread to stream data.  If I continue with this code, I will
probably try to do the same thing but I will have to learn some more about
threading first (another reason to consider adapting the fake_daq code for
now).  

 

Thanks,

 

Lee

 

__________________________________
Lee Nelson
Research Engineer and Laboratory Manager
North Carolina State University
Constructed Facilities Laboratory
2414 Campus Shore Dr
Campus Box 7533
Raleigh, NC 27695-7533
P: 919-513-4793
F: 919-513-1765
www.cfl.ncsu.edu

 

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