PyVisa Query Command fails

[dazz]

Hi
I am restoring an Electro-Metrics EMC-30 receiver. This is a Mil-Spec EMC test receiver that includes a GPIB bus. This is an old piece of kit.
I have built versions of the usbGpib adapter by Xyphro UsbGpib Adapter.
I have been writing and testing very simple test scripts in python with pyVisa.

Write commands sent over the GPIB interface work. When I send a command the receiver responds correctly.

Query commands (write/read) fail for reasons I don't understand.

The following is the code for my test program:
[inline]

# EMC30 simple test
# ver 0.2 date 29 Apr 25
# The purpose of this script is to test manually entered query commands

import pyvisa
import time

print("###### Simple GPIB test for emc30")
print("# Manually enter query commands")
print("# Show the list of Resources")
rm = pyvisa.ResourceManager()
print(rm.list_resources())
rs = rm.list_resources()

print("# Opening the usb:gpib adapter")
emc30 = rm.open_resource(rs[0], send_end=True,)
time.sleep(1)

# get the user input
qy = input("Enter the query command:")
print(emc30.query_ascii_values(qy) )

emc30.clear()
rm.close()

[/inline]

This is a generic test program. It accepts any query command and returns the response.
I always get an error response as follows:

Output:
###### Simple GPIB test for emc30
# Manually enter query commands

# Show the list of Resources
('USB0::0x03EB::0x2065::GPIB_01_34230313836351610051::INSTR',)
# Opening the usb:gpib adapter

Enter the query command:FR
Query the command:  FR

Error:
Traceback (most recent call last):
  File "C:\Users\Darren\Documents\Electronics\emc30_cmd_qry.py", line 26, in <module>
    print(emc30.read())
          ~~~~~~~~~~^^
  File "C:\Users\Darren\AppData\Local\Programs\Python\Python313\Lib\site-packages\pyvisa\resources\messagebased.py", line 485, in read
    message = self._read_raw().decode(enco)
              ~~~~~~~~~~~~~~^^
  File "C:\Users\Darren\AppData\Local\Programs\Python\Python313\Lib\site-packages\pyvisa\resources\messagebased.py", line 441, in _read_raw
    chunk, status = self.visalib.read(self.session, size)
                    ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Darren\AppData\Local\Programs\Python\Python313\Lib\site-packages\pyvisa\ctwrapper\functions.py", line 2336, in read
    ret = library.viRead(session, buffer, count, byref(return_count))
  File "C:\Users\Darren\AppData\Local\Programs\Python\Python313\Lib\site-packages\pyvisa\ctwrapper\highlevel.py", line 226, in _return_handler
    return self.handle_return_value(session, ret_value)  # type: ignore
           ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Darren\AppData\Local\Programs\Python\Python313\Lib\site-packages\pyvisa\highlevel.py", line 251, in handle_return_value
    raise errors.VisaIOError(rv)
pyvisa.errors.VisaIOError: VI_ERROR_TMO (-1073807339): Timeout expired before operation completed.

I think this error is telling me the reply is not being received (timing out).
I have had these query commands working before, so I don't think this is a problem with the EMC-30.

How should I go about troubleshooting this issue? My Python knowledge is poor.

buran write Apr-30-2025, 10:24 AM:
Please, use proper tags when post code, traceback, output, etc. This time I have added tags for you.
See BBcode help for more info.

[deanhystad]

What does the receiver use for read and write termination? You may need to set these for emc30. The pyvisa manual says this is a common cause for the timeout error you see.

https://pyvisa.readthedocs.io/en/latest/...ation.html