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Using VISA/TCPIP under LabVIEW6.0

I need to control an instrument with a LAN connection. I am able
detect the device (TCPIP : : : :20022 : :SOCKET), write to
and read data from the instrument through the MAX 2.0 VISA session.
When I try to send the same kind of command (e.g. *IDN?\n) using
LabVIEW 6.0 VIs I obtain a timeout error when trying to read from the
instrument. I used Visa open, Visa Write, Visa Read, Visa Close VIs.

What is the difference between these two methods and what should I
change to get the LabVIEW VIs to work?


Florent Goldberg
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Hello Florent:

You need to increase the timeout time interval in GPIB read/write vi's since communication is slow over a network. There are example VI's in LabVIEW that do GPIB communication. If you go to the Help menu >> Examples.. >> I/O Interfaces >> GPIB >> "LabVIEW<->GPIB" you will get it. Try tweaking this example.

Hope this helps. If you have any questions, please let us know.

-NI support.
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In general, if it works from MAX (Open VISA Session) then it will work from LabVIEW. As the other post suggested, increasing the timeout usually helps, since the default is 2 seconds. Another thing to try is to right-click on the VISA Read node and change it from asynchronous to synchronous. Sometimes this helps.

If that still doesn't work, I suggest sending our support folks 2 log files from NI Spy: 1 from the Open VISA Session, which works; and 1 from LabVIEW, which doesn't. That might help our tech support see what is going on.

Dan Mondrik
Senior Software Engineer, NI-VISA
National Instruments
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