title: pyvisa unable to connect to GPIB instrument using GPIB-USB-HS interface
body: <p>I'm trying to communicate with an instrument (Agilent 33220A arbitrary waveform generator) using GPIB and I use the GPIB-USB-HS interface plugged into a USB port on my computer.</p>
  
  <p>The instrument is correctly listed when I use NIMAX explorer (there is also a Thorlabs PM100D connected by USB):</p>
  
  <p><a href="https://i.stack.imgur.com/Y6ZNP.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Y6ZNP.png" alt="NIMAX explorer instrument listing"></a></p>
  
  <p>However, I cannot connect to it using PyVISA.
  Here is the code:</p>
  
  <pre><code>import visa
  rm=visa.ResourceManager()
  rm.list_resources()
  </code></pre>
  
  <p>The output is:</p>
  
  <pre><code>('USB0::0x1313::0x8078::P0003982::INSTR', 'ASRL1::INSTR', 'ASRL3::INSTR', 'ASRL6::INSTR')
  </code></pre>
  
  <p>As you can see, the PM100D connected by USB is correctly listed, but not the Agilent connected on GPIB 10.</p>
  
  <p>I tried to connect directly:</p>
  
  <pre><code>rm.open_resource('GPIB0::10::INSTR')
  </code></pre>
  
  <p>But I got an IO error:</p>
  
  <pre><code>Traceback (most recent call last):
    File "&lt;stdin&gt;", line 1, in &lt;module&gt;
    File "c:\users\nanotube\appdata\local\programs\python\python36\lib\site-packages\pyvisa\highlevel.py", line 1623, in open_resource
  info = self.resource_info(resource_name, extended=True)
    File "c:\users\nanotube\appdata\local\programs\python\python36\lib\site-packages\pyvisa\highlevel.py", line 1583, in resource_info
  ret, err = self.visalib.parse_resource_extended(self.session, resource_name)
    File "c:\users\nanotube\appdata\local\programs\python\python36\lib\site-packages\pyvisa\ctwrapper\functions.py", line 1381, in parse_resource_extended
  alias_if_exists)
    File "c:\users\nanotube\appdata\local\programs\python\python36\lib\site-packages\pyvisa\ctwrapper\highlevel.py", line 188, in _return_handler
  raise errors.VisaIOError(ret_value)
  pyvisa.errors.VisaIOError: VI_ERROR_RSRC_NFOUND (-1073807343): Insufficient location information or the requested device or resource is not present in the system.
  </code></pre>
  
  <p>I use Python 3.6.0 on Windows 7 Pro 64 bits OS. PyVisa version is 1.8.</p>
  
  <p>I don't understand what I'm missing here. Does anyone have an idea ?</p>
  
  <p>Many thanks !</p>