GPIB receive query

[AndreaD]

I am using the solar array simulator, E4350B and I am controling it with LabVIEW through GPIB. When I do a query/sense voltage/current on one solar array simulator, I was able to obtain a query/sense value to display. This was through using a GPIB receive. But when I try to connect two SAS together, then the message displayed through the receive were random output characters. In my configuration, I have two GPIBs connected together with another GPIB cable connected to a chassis. I believe that this would connect the power supplies in parallel, if I am not mistaken. If it is connected in parallel, then one value should be displayed. Would I be able to display a correct value from the output rather than alot of noise? I believe the problem is with the GPIB connection and perhaps I am using the GPIB incorrectly. 

Thanks, 

Andrea 

[Dennis_Knutson]

What exactly do you mean by 'two GPIBs connected toegether'? If you mean you have a GPIB cable between instrument A and instrument B and another cable going to the GPIB controller, that has nothing at all to do with placing the power supplies in parallel. They are still separate supplies that can be addressed separately and must have different addresses. To actually connect the supplies in parallel, you have to wire the voltage outputs together. Again, parallel supplies have nothing to do with the GPIB connection.

[AndreaD]

Okay, thanks for the clarification ... so  I did not connect them in parallel.

I connected a GPIB cable between instrument A and instrument B. I have a discrepency with what you said about the different address as well -- so if I addressed them with the same address, then they both changed at the same time, hence I thought they were in parallel. Why when I query/sense them, they provide random characters at the output? Is it with the nature of GPIB connection, or is there a way I can bypass the problem? 

Thanks, 

Andrea 

[Dennis_Knutson]

They HAVE to be set to different addresses. You HAVE to query them individually. That is a basic requirement of GPIB.

[AndreaD]

I have another problem with the GPIB ... 

I have two SAS, A and B, where A is the first power supply to be attached to the chassis and B is not directly connected to the chassis. When I address A and B with different addresses -- where A is addressed correctly by labview with the correct address and B is not addressed correctlly by labview with the incorrect address setting on the SAS -- it does not give an incorrect message. But when switched -- so A is addressed incorrectly by labVIEW with respect to the SAS and B is addressed correctly by labVIEW with the correct address -- then I receive an error message. This does not make sense to me at all ... am I doing anything wrong?

Thanks, 

Andrea 

[Dennis_Knutson]

I don't understand what you mean by chassis, why you are not using the correct addresses, or the error message. What is the exact error message? Is it generated by LabVIEW or the instrument?

Why don't you go ahead and post your program?

[AndreaD]

Here is my program ... it's a pretty simple control.

What I mean is this: Given SAS A and SAS B, implemented at addressA and addressB respectively on the power supply level, addyA and addyB on the LabVIEW level respectively, 

I run the labVIEW program, intentionally setting so addressA != addyA and addressB = addyB (for the purpose of testing the program, this gave an error. 

Unforrtunately, when addressA = addyA and addressB != addyB, then this did not give an error. 

The error I received is out of the receive, error (6).  This does not make sense to me --I would think both scenarios would give problems.

Thanks, 

Andrea

[Dennis_Knutson]

What is with the MakeAddr function? I thought you have two distinct instruments. Save the MakeAddr for the weird single instruments that need primary and secondary addresses.

You might want to search the web for some basic GPIB tutorial. I would also recomend you use the VISA functions instead of the lower level gPIB ones. Your code will be more portable.