open session failure

[wwwwwww]

Hi I am issuing some commands to my device via NI-VISA through TCP/IP.

Here is what i do:

1.open session

2.some application specific commands

3.close session

These three steps are done multiple times and it seems most of the time the communication is fine. Once in blue moon i get an error from ni visa : 

Failed to open session - Check TcpipSocket connection at address x.y.z.a(Failed command: OpenSession)

I check the device and it is running on the ip  x.y.z.a, i close ni visa and reconnect to the same ip and issue *idn? i get a valid response back. I dont understand what is causing the open session to fail intermittently

thanks

[nyc_(is_out_of_here)]

open session ONCE at start of program

close session at end of program

[wwwwwww]

Hi nyc,  thanks for the quick reply

heres what i do..

I do open session once. do the application code and close the session on that unit

but sometimes i have two or more devices connected. So i  close session on the existing unit and open new session on another unit do application code and so on.

after some time when i get back to the old unit (for which i previously closed session) to open session, it fails sometime

[crossrulz]

You can leave the session open, even when you are talking to multiple instruments.  Imagine a test system with 10 ethernet instruments.  Are you telling me you would open and close the sessions each time you change which instrument you are talking to?  No.  Open a VISA session for all of your instruments and then close them when your software shuts down and your life is a lot simpler.

[wwwwwww]

Hi crossrulz,

But technically I should be able to open and close session multiple times, which i am able to do most of the times.

I will try your suggestion but if it works, i am not sure what the root cause of this intermittent open session exception was.

I saw a similar post where ni-visa read hangs for driver V5.0.3 and above, i am using ni visa version v5.4, I dont know if these are related

http://forums.ni.com/t5/Instrument-Control-GPIB-Serial/VISA-Read-hangs-Get-Resetting-VI-dialog-on-ab...

thanks

[DangerDave]

Hi wwwwww,

I did a quick search for your error, but didn't find anything that seemed related.  It's obviously not the a perfect explanation, but nyc is right.  Opening and closing sessions once will very likely fix your error, since that's the way those VIs were designed to be used.