VISA: how many usb resources can be opened simultaneously?

[AlexanderKhodarev]

I can not open more than 30 usb VISA resources (LV 7.0 WinXP). Is it a fundamental limit of some sort? And if it's not, how can i overcome it?
(I've already posted the same question some time before)

[sergesl]

Hi Alexander Khodarev

What happens when you try to open more than 30 USB VISA resources?

Serges Lemo
Application Engineer
National Instruments

[AlexanderKhodarev]

Hello Serges Lemo.
Following thing happens: after 30 VISA's are opened i can't open no more usb visas. It means that no new VISA resource appears when new usb device is connected to computer. After that i have to quit labview (that sometimes leads to the system error). Unfortunately it means that i can not open >30 devices at a time. Do you know anything that can help?

[sergesl]

Hello Alexander,

I am not quite sure what the maximum number of VISA USB sessions you can open simultaneously. However, I believe it should not be as low as 30. I suspect that you may be using GPIB resources instead of USB resources.
If you are using USB resources, which device are you using? In addition, I would like to know if you are opening these sessions to different physical USB devices.

Serges Lemo
Application Engineer
National Instruments

[AlexanderKhodarev]

Hello Serges.

I definitely do not use GPIB interface. I'm so sure because this device is homemade and simply do not have GPIB:) By the way it's step motor controller.
And i do open sessions to different physical devices, and when 30-th device is connected no VISA resource is generated for it.
You know, i've recieved another answer that hint's, that device can use more than one slot of the usb bus. Do you think this is the case?
Thank you in advance.

Alexander Khodarev

[JoshuaP]

Does Windows detect that an additional device has been inserted and does it show up in the Windows device manager as a VISA device?

I don't know how you have all of these devices connected, but I am assuming they are all connected to one hub. Try adding the 31 device to a different USB port on the computer. The USB port you are using might have a limitation.

-Josh