How to read from two instruments via GPIB? 
Author Message
 How to read from two instruments via GPIB?

Hi, I am new to labview. Now my job at hand is to read two values
spontaneously from two GPIB instruments. I make use of VISA
(open-...-close) to read from the two respectively. Do I need to close
one visa channel for one instrument in order to read the data from the
other instrument? and it seems very complicated to connect "Visa
Session" and "error" all over my program, is it a pure GPIB read,
write better, since it is simple, just an icon representing different
command?


Tue, 06 Jul 2004 22:26:18 GMT  
 How to read from two instruments via GPIB?
No, you can have multiple sessions open at the same time. What version
of LabVIEW are you using? Some older versions require the open...close
structure for GPIB, but the newer ones do not.

The GPIB read and write, skips all the VISA stuff. When you do a VISA
read (or write), the software sends the information to the VISA
driver, where the name of the instrument is looked up in a table, the
command is changed to a GPIB format and sent to the GPIB driver.
Direct GPIB read and write skip the middle-man. Direct GPIB read and
write are faster, but for most cases, people won't see the difference.

     Rob



Tue, 06 Jul 2004 23:53:30 GMT  
 How to read from two instruments via GPIB?
Hi There,
You will need to set (on the instruments themselves) different GPIB address.
With VISA you can have multiple devices open simultaneously, so you can make
your program parallel.
Use a "sequence" control box to synchronize the read operation of both
instruments (put the request/read commands for both instruments inside the
same (single frame) sequence.

BTW if you are calling the instruments for data more than once, and you open
and close the visa sessions to the instruments outside the For/While loop
then -  don't forget to use "shift-register"s in your loops for  the inst.
handle and error in/out or u run into lots of difficult to trace problems...

 good luck,
Peter


Quote:
> Hi, I am new to Labview. Now my job at hand is to read two values
> spontaneously from two GPIB instruments. I make use of VISA
> (open-...-close) to read from the two respectively. Do I need to close
> one visa channel for one instrument in order to read the data from the
> other instrument? and it seems very complicated to connect "Visa
> Session" and "error" all over my program, is it a pure GPIB read,
> write better, since it is simple, just an icon representing different
> command?



Wed, 07 Jul 2004 00:30:56 GMT  
 
 [ 3 post ] 

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