Is it possible to read SMU voltage/current after closing the original session?

[bholsinger]

What is the method, or is it even possible, to read the live voltage and current measurements from a PXIe-4138 SMU after the original configuration session has been Closed?  I have a (relatively) long-running Teststand sequence that configures the SMU to deliver power to the DUT, then performs tests and along the way I need to take the SMU readings.  I've always been under the impression it's best practice to open, configure, and close the SMU quickly, but the 3-state programming model doesn't seem to allow a way to jump back into the Running state from Init with Channels VI, except by going through Uncommitted and Committed states, and thereby shutting everything down in the process. The Power Measure VI only works if you're in the Running state. Seems like a no brainer, so what am I missing?

[crossrulz · Accepted solution]

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@bholsinger wrote:

I've always been under the impression it's best practice to open, configure, and close the SMU quickly

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That is BAD advice.  You open at the start of your program, you do whatever you need to with it inside of your test program (configure, read, etc) and you do not close the session until you are shutting down your program.

[bholsinger]

Is the best practice to open the SMU at the beginning of the test sequence, and store the reference into a file global?  We have multiple different VI's that need to access the SMU (sometimes just to read the measurements, without changing any running parameters), and all those VI's will now have to be re-written to reference a global teststand variable, which won't exist when the VI is run stand-alone.  Now it becomes more difficult when developing VI's that access the SMU: we can't just run the VI by itself to test the functionality, now we have to run it inside a TestStand sequence that opens and closes the instrument.  

Advice is very welcome. Thanks!

[crossrulz · Accepted solution]

I store my instrument reference in an Action Engine, so it stays independent of TestStand.