Alias in NI Max Resets to Default

[ljark]

I have Visa Alias setup for COM3 to "UUT".  From time to time the system will stop communicating and what we are finding is that the Alias is no longer set to "UUT", but COM3.  There was no hardware change.  This seems to happen randomly and typically after a system is powered down for a period of time or even a weekend.  I have multiple setups and it does not seem to happen on them all.  I also have seen it happen on different revisions of NImax.  Any suggestions are appreciated.

[bahannah]

ljark,

NI MAX stores the alias information in the visaconf.ini file. I do not know what operating system you have, but on Windows 7 it can be found in the following directory: C:\ProgramData\National Instruments\NIvisa

Do you know if visaconf.ini is being recreated each time that your system is powered down? Does your IT department or your computer change files around in the directory or create a new file each time?

Regards,

Hannah 

Applications Engineering 

National Instruments 

www.ni.com/support 

[ljark]

I have seen it happen on WIN7 and WIN2K.  The files should not be moving around or changing.  Everything is local.  Possibly there is some script running from IT that causes the file to be stalled or possibly the virus software is seeing is and deleting it.   Not sure what would be deleting the ini file. It doesn't happen everytime and not on every system.  Sometimes it can weeks/months without an issue.

[Kyle97330]

Assuming you don't change anything else about your setup on a regular basis, could you set the visaconf.ini file to "Read-only" and see if that stops it?

[David-n-MO]

I have exactly the same problem on a windows10 pxie chassis running LabVIEW 2018 sp1 that has never been on THE network. It happens enough that an engineer wrote a quick program to refresh the file when it occurs, but I'd really like to know what is happening. 

[ljark]

Unfortunately, I have never been able to figure this one out, so we have just been living with it.  I trained all the techs and put snips on the desktops to show what it should be so we can quickly reset.

[JÞB]

COM3 is never a really cool serial enumeration.  BT, WIFI, mice and other HID devices like to fight over it when the plug n pray (sic) routines get involved. That makes your expected serial device grab another available COM enumeration and the VISA Alias becomes unbound from the responsible serial enumerator for your Virtual COM Port driver.

A few things you can try to make it more robust;

• Use the device manager to select something like COM13 that is less likely to create a contention. Your device will then want to plug in at COM13 again and the VISA Alias becomes stabler.
• Use the System Configuration API to programmaticly reassign the resource Alias as seen here.  The filters will find your device no matter what serial enumeration plug n pray assigns as long as it exists. Then forces it to use your Alias.  Very handy when the VCP is actually part of the UUT.

[JB]

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@ljark wrote:

Unfortunately, I have never been able to figure this one out, so we have just been living with it.  I trained all the techs and put snips on the desktops to show what it should be so we can quickly reset.

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The same goes for us. With many applications in use, we also regularly encounter this problem. A common case is the alias for a USB connected printer. Having never been able to identify the cause of these disappearances (without having spent much time investigating) we have either deleted these aliases or explained to the people concerned how to restore them.