I can't get multiple instruments running with GPIB-USB cables

[Ace02]

I am trying to control two seperate function generators.  I can only get one machine to work at a time.  Under the Measurement and Automation Explorer it finds one instrument under GPIB0, and the other under GPIB1.  Only the machine controlled by GPIB0 works.  The program I have written is in the block diagram format of Labview.  How do I get this program to run both GPIB connections?

[Dennis_Knutson]

Do you actually have two GPIB controllers? If you do, why? If you don't, then something is corrupt in the installation. Even with two separate controllers, you should not have a problem controlling either. If you really do have two GPIB-USB controllers, can you post your code? Make sure you have the front panel controls set. Select the VISA Resource Names and then go to the Edit menu and select 'Make Current Values Default'. Save the VI and then attach it.

[Ace02]

I have two separate controllers because I have a GPIB-USB cable that connects each function generator to the computer, and to me it appears that with those kinds of cables that is how it is automatically setup.   As far as my code goes, I set it up using the block diagram method, and so I'm not sure how to post it.  Is there an option from the window diagram that I can use that will display a script version of the code?  I am just barely learning to use Labview, so I am not sure exactly how to do that.

[Dennis_Knutson]

I'll bet you made the people from NI happy by buying two controllers but it is usually a waste of maoney when all you need is a simple cable to connect instrument 1 to instrument 2. Save the extra controller for another project and just connect with a cable. Just make sure that each instrument has a unique address I'll bet all of your problems go away. Look for a GPIB tutorial to learn the basics.

A VI is just a file and there is no such thing as a script version so I have no idea what you mean. Just click the 'Add Attachment' that you should see right below the message body. Browse to the file. Select it. Easy.

[LeifKing]

I would also agree that for 2 instruments using 2 GPIB-USB adaptors is a bit of a waste, but the addressing by using 2 may also be part of your problem.  Part of the solution may be dependent upon what portions of LabVIEW you are using with these devices as the methods vary, but I would recommend checking in Measurement and Automation eXplorer for the details of both the configurations of the GPIB0 and GPIB1 and see if both are set as system controllers and the primary address settings (as sometimes even though one is GPIB0 and the other is GPIB1 they both are fighting over the "0" primary address which is independent of the controller name (referring to the GPIB0 and GPIB1 designations)) as well as the address settings of the 2 instruments.  Even though you are using 2 different controllers, the address can still be limited to the same range for certain functions and as you are using 2 of the same type of instruments I'm guessing they are 2 of the same manufacturer and model and so probably both have the same default address.  The solution may be as simple as changing the address of 1 of the units.  The reason why is in for instance using some of the more advanced VISA functions in a VI the instrument addresses may be differentiated (I haven't tried it and I avoid having any 2 instruments on the same address regardless so I don't know for sure) by the controller by one being GPIB0::10::INSTR with the other being GPIB1::10:INSTR, but for the basic VI functions of GPIB read and GPIB write these functions only take the 10 part of the address and so both instruments therefore have the same address and there is then a conflict.  Depending on which controller is the primary (usually GPIB0) the instrument connected to it usually takes precedence if either works at all.  In MAX you can sometimes simply re-assign the address ranges of the instruments connected to each controller, but I've never found experimenting with this necessary.

[Dennis_Knutson]

There is a bit of information in your post that needs clarification. If the controllers are connected to separate instrument busses, there is no need at all to be concerned with making one primary or secondary and instruments on the separate busses can have identical addresses. This situation is not uncommon when there are more than 15 instruments that need to be controlled or when you need parallel communication.

[LeifKing]

Again as I said provided you use the full addressing or Visa addressing that includes the bus address.  It is easily possible, but only if you remember to do that each time.  I often find the standard GPIB functions easier and faster to process especially for older instruments than the VISA equivalents.  If an instrument is set for address 22 most people just would use a GPIB read or write function sending the address of just a string of 22 rather than using the 0+22 sting for instrument of address 22 on bus GPIB0 and 2+22 for an instrument with address of 22, but on the bus GPIB2. So you do have to be careful as just sending 22 will ONLY read from the instrument on the bus designated as the primary or the system controller which sounds like could be the case here.  For VISA addresses it is rather obvious and easy, but I only found out that you can use the bus+address for the regular GPIB addresses a few weeks ago while I've been messing with LabVIEW to some extent here and there for over 5 years now.  Like some things in LabVIEW it is well explained in the help files, but often not at the immediate first place you would think to look such as the help on the GPIB pallet such as the GPIB read/writes functions.  I found out while researching a problem I was having that was completely unrelated.

[Dennis_Knutson]

Still you mistake the facts. With two controllers, you do not designate one as the primary or system controller. Each is the system controller for it's own bus.