VISA Resource

[BlueShift]

I have written a VI to communicate with an RTD calibration bath that is linked to the computer with an RS-232 cable.  Generally, it is working just fine, but after running for a while, communication ceases.  After investigating, I have discovered that the VISA session that I am giving to a couple of Instrument I/O assistants has been cleared.  Despite my best efforts, I have been unable to eliminate this problem.  

I have attached the VI that I am using to communicate with the bath for reference purposes.  The global variable "New Setpoint" is used only when a new temperature setpoint for the bath has been input.  The "Read Channel" VI reads from a data array that is storing data, and is constructed in such a way that it can easily be linked with a Keithley sampling device and used with configuration files.  

The variable and data wire for "Bath Session" is what I am having an issue with.  Again, when I first run the VI it has no troubles finding the bath and communicating with it, but after a while (the time is inconsistent on when it stops working), the data wire seems to clear itself and thus cannot communicate with the calibration bath.

Any insight into this issue would be greatly appreciated. 

[BlueShift]

One more thing, I am not getting an error messages.  I have checked numerous times and there appear to be no errors.  The VISA session just stops reading without any indication as to why.

[RTSLVU]

Right off the top of my head I would say dump the Instrument I/O assistants and just use VISA reads and writes to comunicate with your instrument.

Personaly I have not had good luck using any of the "express" VI's.

[Swathi B]

Hi BlueShift,

Have you had a chance to replicate this behavior with lower-level VISA commands? The Basic Serial Write and Read.vi, accessible from NI Example Finder, has the associated code you may be interested in. 

You could post an NI Spy Capture file that identifies driver calls and results, and the following KnowledgeBase article details the necessary steps.

Performing a Good NI Spy Capture for Debugging/Troubleshooting

[BlueShift]

Thanks for the suggestions.  After some work, I was able to fix the behavior entirely by controlling the calibration bath using VISA reads/writes.  The Instrument I/O assistant didn't seem to allow enough time between writes/reads for the temperature bath to process the command and then return the requested value.  This was easily accounted for by a wait placed in a sequence.