VISA issues with Keithley 236

[Baaz]

I'm using the Keithley 236 in LabVIEW 8.5 and am having some VISA issues.  I cannot find a write buffer command that works with the 236.  Does anyone know any?  If you need more details ask, but I can't provide you with the vi because its ITAR restricted.

[Sammy Z]

Hi Baaz,

Where have you seen that vi?  I don't see that vi being included with the instrument driver for Keithley 236. 
What ae you trying to accomplish?

Thanks,
Sammy Z.

[Baaz]

Hi Sammy, I am trying to adapt the Keithley to some existing VI, but maybe its just not the best way to do it.  Basically I am trying to do a computer controlled voltage sweep to test the operation of a device.  I'm only using the Keithley as a voltage source because it does not have enough resolution to properly measure the signals we are after.   For the measurements I am using two Agilent (HP) 34401A Digital Multimeters, both connected to the computer with GPIB.  So basically, I want to set a voltage, take a four wire resistance measurement off of those two DVM's, plot a point on a graph and then repeat until I hit my top level voltage.  I have some existing code but if Keithley 236 isn't set up to jive with VISA perhaps I should just create a whole new VI.  Let me know what you think.

[Dennis_Knutson]

I don't think you have explained what the exact problem is. What happens when you try to do a VISA Read or Write? Do you get an error returned or something else? Have you tested the commands in MAX with both the VISA test panel and GPIB communicator? Do any of the commands work there? Does the instrument require any other termination besides EOI? Have you tried adding other termination characters. What does the instrument manual say about this?

VISA is just an API that sits above the low level GPIB functions so if you can use the GPIB functions, there's no reason that you should not be able to use VISA.

[Baaz]

Dennis, I have not tried some of the things you listed.   When I VISA write to the device it returns the error message 'IDDC'.  I have been searching the manual for it but its written for using BASIC, so I'm not getting very far.  If you haven't noticed I'm a noob to LabVIEW, so if you could further explain some of your suggestions (IE how to use the test functions) I would much appreciate it.

[Dennis_Knutson · Accepted solution]

What is 'it' that returns IDDC? That's not an error code from VISA.

What I am suggesting is that you forget about LabVIEW for the time being and concentrate on debugging some basic GPIB communication. In MAX, under Device and Interfaces your GPIB card should be listed and under that should be listed the instrument if you followed the installation instructions. If the instrument is not listed, right click on the controller and select 'Scan for Instruments'. When and if the isntrument is listed, you can right click and select 'Communicate with instrument'. You have the option of doing a write, read, or query. This is where you should start debug of the commands.

[Baaz]

The 'IDDC' message comes up on the instrument and in my error out window in LabVIEW. 

Thank you for your advice, as previously stated, I was unsure of what you were telling me to do, but will now follow your advice.  I am just starting the transition from Undergrad to Graduate Studies so my experience with practical applications is limited, thank you for being patient and forthcoming with me.

[Dennis_Knutson]

Hopefully, the instrument manual has an explanation of what IDDC is supposed to mean. Understanding that may be key to getting your progam working.

[Baaz]

Dennis, your help was invaluable, I believe I am on my way to figuring this out.  Sadly I was sort of thrown to the wolves for this project (I didnt even know what MAX was) but at least I am being shocked into learning LabVIEW because of it. 

IDDC just meant that I was sending an improper write command to the instrument.   My predecesor took/lost the manual to the instrument but Keithley was kind enough to provide me with an electronic replacement so I am on my way to solving my problem.  Again, thank you very much for your assistance, you truly are an NI Knight.

[Baaz]

As an update, I was able to resolve my issue and get my VI working.  Once again, thank you Dennis.