[newbie] problem with module PyVisa

[Jean Dubois]

I'm trying to control a programmable power supply via USB using
python.
After doing some googling I thought I should use PyVisa for this
purpose, so I installed it as follows:
tar xvfz PyVISA-1.4.tar.gz
cd PyVISA-1.4
python setup.py install

Installation seems to finish without errors.

When I start a python session things go wrong as you can see in the
output below,
can anyone here tell me how to proceed correctly? thanks in advance.
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/local/lib/python2.6/dist-packages/PyVISA-1.4-py2.6.egg/
visa.py", line 1, in <module>
from pyvisa.visa import *
File "/usr/local/lib/python2.6/dist-packages/PyVISA-1.4-py2.6.egg/
pyvisa/visa.py", line 231, in <module>
resource_manager = ResourceManager()
File "/usr/local/lib/python2.6/dist-packages/PyVISA-1.4-py2.6.egg/
pyvisa/vpp43.py", line 105, in __new__
it.init(*args, **kwds)
File "/usr/local/lib/python2.6/dist-packages/PyVISA-1.4-py2.6.egg/
pyvisa/visa.py", line 227, in init
self.session = self.vi = vpp43.open_default_resource_manager()
File "/usr/local/lib/python2.6/dist-packages/PyVISA-1.4-py2.6.egg/
pyvisa/vpp43.py", line 758, in open_default_resource_manager
visa_library().viOpenDefaultRM(byref(session))
File "/usr/local/lib/python2.6/dist-packages/PyVISA-1.4-py2.6.egg/
pyvisa/vpp43.py", line 175, in __call__
self.load_library()
File "/usr/local/lib/python2.6/dist-packages/PyVISA-1.4-py2.6.egg/
pyvisa/vpp43.py", line 146, in load_library
self.__lib = self.__cdecl_lib = cdll.LoadLibrary(path)
File "/usr/lib/python2.6/ctypes/__init__.py", line 431, in
LoadLibrary
return self._dlltype(name)
File "/usr/lib/python2.6/ctypes/__init__.py", line 353, in __init__
self._handle = _dlopen(self._name, mode)
OSError: /usr/local/vxipnp/linux/bin/libvisa.so.7: cannot open shared
object file: No such file or directory

 

[Rodrick Brown]

It seems pretty obvious from the error. Try installing the missing lib packages.

OSError: /usr/local/vxipnp/linux/bin/libvisa.so.7: cannot open shared
object file: No such file or directory


Sent from my iPhone

 

[Jean Dubois]

It seems pretty obvious from the error. Try installing the missing lib packages.

OSError: /usr/local/vxipnp/linux/bin/libvisa.so.7: cannot open shared
object file: No such file or directory

Sent from my iPhone

The error may be obvious but finding this file and how to install it
is not unfortunately.
It seems I have to install it from the National Instruments site but
Debian Linux doesn't seem to be supported...
and I doubt whether just copying this file will be sufficient to make
PyVisa work.
I wonder whether there might be another way to communicate via USB
with a Keithley programmable power supply using Python.

best regards,
Jean

 

[Prasad, Ramit]

The error may be obvious but finding this file and how to install it
is not unfortunately.
It seems I have to install it from the National Instruments site but
Debian Linux doesn't seem to be supported...
and I doubt whether just copying this file will be sufficient to make
PyVisa work.
I wonder whether there might be another way to communicate via USB
with a Keithley programmable power supply using Python.

Here are some reference links that might help.
http://stackoverflow.com/questions/8140248/linux-implementation-of-visa-api
https://decibel.ni.com/content/message/37590


Hope that helps,
Ramit


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[Jean Dubois]

I've been using pyserial quite successfully to control a USB-to-serial converter.

That is, controlling a couple of RS232 serial devices via the USB port through a KeySpan USB-to-Serial converter.

Pyserial seems to make communication through the USB port quite transparent, at least on my OS-X system.

-Bill

Well, in fact I do have some working scripts using pyserial to control
an older (and more expensive) Keithley sourcemeter in combination with
a USB-to-serial converter.
But the trouble started when buying a cheaper and newer Keithley model
which does not have rs232 but only USB. I noticed they have put an
extra layer above USB called USBTMC
which complicates things further. I followed the instructions at
http://www.home.agilent.com/upload/....htm?&cc=BE&lc=dut#3.Copyright Notice|outline
and compiled and loaded the usbtmc-driver but I still can't
communicate with the Keithley, hence I started looking for an
alternative using PyVisa...and now I'm stuck

jean

 

[Jean Dubois]

Well, in fact I do have some working scripts using pyserial to control
an older (and more expensive) Keithley sourcemeter in combination with
a USB-to-serial converter.
But the trouble started when buying a cheaper and newer Keithley model
which does not have rs232 but only USB. I noticed they have put an
extra layer above USB called USBTMC
which complicates things further. I followed the instructions athttp://www.home.agilent.com/upload/cmc_upload/All/usbtmc.htm?&cc=BE&l...outline
and compiled and loaded the usbtmc-driver but I still can't
communicate with the Keithley, hence I started looking for an
alternative using PyVisa...and now I'm stuck

jean

I finally got it working without PyVisa as follows:
#!/usr/bin/python
#sample program for Keithley 2200 USB
#first compile and load module usbtmc
import os
usbkeith = open('/dev/usbtmc1','r+')
#next commando is very important
#without it you can fetch data but not SET data
usbkeith.write("SYST:REM" + "\n")
usbkeith.write("*IDN?\n")
identification=usbkeith.readline()
print 'Found: ',identification
usbkeith.write("SOUR:CURR 0.2A\n")
usbkeith.write("SOUR:OUTP:STAT ON\n")
usbkeith.write("MEAS:VOLT?\n")
measurement=usbkeith.readline()
print 'Measured voltage: ',measurement

regards,
jean