Group Execute Trigger on 2 DMMs

[GeoffF]

Hi there,

I'm trying to use Software Triggering to trigger two Agilent 34401A DMMs "simultaneously".  I've found this article from 2007:

http://forums.ni.com/t5/LabVIEW/How-do-I-use-VISA-to-perform-GET-Group-Execute-Trigger-to-three/m-p/...

However, the answer is less than useful, since it does not address the question.

What I'm trying to use is the GPIB 488.2 Trigger List function (as recommended by NI).  However, generating a list programmatically is proving a touch ... interesting.

Given that the device selection is done using VISA aliases, I am trying to use a property node to extract the GPIB address.  As a temporary trial, I'm using a VI with the code in the attached snippet included.  With DMMs configured at GPIB0::6::INSTR and GPIB0::22::INSTR (but trying this from home with no actual hardware attached), my probe is showing all the property values as 0.

Have I tried the wrong approach?  Would trying this at the office with the DMMs attached produce a different result?  (I'll try again tomorrow anyway.)

Any and all comments would be appreciated.

Regards,

Geoff

[GeoffF · Accepted solution]

Trying from work with the DMMs connected (and turned on), the Primary Address property returns exactly what I expect and the code snippet works - apparently - perfectly.

I had been struggling with getting the DMMs to trigger and with retrieving the measurements from the DMMs.  I was trying to use the "Trigger" function, but it didn't seem to work without extra steps to ensure the right listeners are selected - hence the "Trigger List" function.  I also had issues retrieving the data - partially because it (probably) hadn't trigger, but mostly because I wasn't waiting long enough for all the samples to be retrieved.

For information, this system has (by default, but configurable) 10 samples being read at 0.1s intervals, so it needs to wait for a second.  I could just have increased the timeout, but that's a bit messy.  Alternatively, I suppose I could loop waiting for the signals to be ready, but the driver set for this DMM doesn't seem to include a query function.

The VIs with a timer symbol on them simply contain a Wait (ms) call.  It's cleaner (in my view) than putting it in a frame.  Now that I have the function working, I've also replaced the timestamp and trigger function frame with a sub-VI.

Regards,

Geoff