Instrument Control (GPIB, Serial, VISA, IVI)
PyVISA cannot communicate with Keithley2400 using Prologix GPIB-USB
There is no actual error in pyvisa-info to be seen. Yes it says that gpib_ctypes could not find the NI GPIB library. But that's normal, that library only will work with the NI hardware.
The Prologix interface is simply a serial device that implements a GPIB interface on the remote side. But in order for this to work there needs to be an intermediate driver that sits between your pymeasure module implementing the Keithley driver and the actual pyvisa library accessing the serial port. Unless pyvisa or pymeasure itself supports such a GPIB to VISA_COM translation shim specifically for Prologix, there won't be anything the pymeasure module can do with your serial port resource you open. If you pass a serial port resource to pymeasure it will attempt to send the instrument commands to it but somehow it also should control the GPIB function of the Prologix device.
One option would be if Prologix itself provides a NI-GPIB compatible DLL. In that case you could as recommended in the pyvisa-info log issue something like this before trying to importing pyvisa:
import gpib_ctypes
gpib_ctypes.gpib.gpib._load_lib(PROLOGIX_GPIB_DLL_PATH)
import pyvisa as visa
But that driver would have to be provided by Prologix.
But from the Prologix site:
Is Prologix GPIB-USB controller a drop-in replacement for controllers from other vendors?
No. Prologix GPIB-USB controller provides a virtual serial interface to communicate with instruments, while handling all GPIB protocol details for you. Programs that expect a different interface (such as NI 488.2 interface) have to be modified to use the serial interface to be compatible with Prologix GPIB-USB controller.
Basically this means that PyVISA or PyMeasure (but I would think that it is more logical to add this to PyVISA) would need to be modified to support the Prologix interface by providing the necessary translation. While a normal PyMeasure driver simply tries to send instrument commands through the provided VISA connection resource this won't work since the Prologix device needs additional commands to setup at least the mode, auto and device address, before the actual device commands can be sent to be passed to the device.
And that PyVISA modification would get quite a bit more complicated if you wanted to support multiple GPIB devices at the same time.
Basically, using a Prologix device may seem very cheap in comparison to an NI device, until you start to count in the many hours you need to make it work.
No, pyVISA does not need a GPIB driver if you use a Prologix interface. Prologix is as far as pyVISA is concerned simply an RS-232 device.
But if pyMeasure provides some Prologix compatibility shim as you say, there must be a method or property in the pyMeasure driver to enable that and program the GPIB address of your device. I didn’t see a GPIB address to the Prologix class constructor in your example as is documented to be required in the pyMeasure documentation. Instead you try to set it later on through some other means but that looks much more complicated. Why don’t you try to do it as mentioned in the documentation?
Of course there is actually a real chance that with all your attempts to install and deinstall all kinds of NI driver software, you messed up NI-VISA itself that something doesn’t work right and that can be a hassle to untangle if the MSI database got somehow corrupted.
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