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How much VISA resources can be opened simultaneously?

How much VISA resources can be opened simultaneously?

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Message 1 of 10
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Hi Alexander,
I've never had any problem when opening VISA resources.
I'm developping a software that involves GPIB instruments and I've tested it with up to 15 different instruments connected on two different buses and I didn't have any problem so far. (Each GPIB address needs its proper VISA resource).

Hope this helps !
Julien
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Message 2 of 10
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Are you having a problem, or is this a theoretical question?

There is a limit but it is adjustable. By default you should be able to open up to about 250 sessions, but your mileage may vary greatly depending on the type of resources you are opening. If you are having problems well below this limit, then there may be some other type of problem than the one I am thinking of.

But if you are getting around 250 sessions and need more, there are some INI tokens that you can change. While we don't typically document them, I can make an exception. Just let me know if that's the case.

Dan Mondrik
National Instruments
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I have a problem in following: when i'm using VISA usb devices i cannot open more then 32 sessions. After they are opened no new VISA can be created. And after i quit Labview (to close all sessions automatically) there is a chance of computer reboot. Is 32 a strict limit, or i can change something somewhere to increase it?

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Hello!

 

I have similar problem, I can open and communicate over 8 serial VISA sessions, but if I open and use one more, then my programm is running more slowly. It seems to block other sessions in reading state.

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Although you can have many sesison open only one can be active on the GPIB bus at a time.

 

If you are using serial, then a shared VI between your threads may introduce delays. Check for re-entrancy on common sub-VIs.

 

Of course repeatedly opneing and closing ports will get in the way of each other.

 

Ben

Retired Senior Automation Systems Architect with Data Science Automation LabVIEW Champion Knight of NI and Prepper LinkedIn Profile YouTube Channel
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Thank you, Ben!

 

I use RS232, no GPIB

I don't use any VI, which reads the interface and is not reentrant

I open and close interfaces once, not before each reading

 

Do you have more ideas, what I can check to solve the problem?

 

Regards, Eugen

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POst a set of images showing the code that seems to be interfearing with each other.

 

Ben

Retired Senior Automation Systems Architect with Data Science Automation LabVIEW Champion Knight of NI and Prepper LinkedIn Profile YouTube Channel
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Message 8 of 10
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It's not possible, the project is too big (about 6000 VIs), and all the VISA functions are in many SubVIs.

But, one more information.

I use 3 interfaces with 6 sessions (for each read and write session simultaneously) and 2 interfaces only for write, and 1 interface with one session for reading and writing none simultaneously.

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The problem disappers if I close one of read sessions, independantly of the number or function.

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