Iterative calculation - retaining and using values

[bunnykins]

It may have been my mistake in the file that I previously sent in to the discussion board, I did reconfigure the parameters to 1 second intervals to ensure that the simulation time clocked through in exactly 1 second steps.

May I ask your advice about the attached vi file that currently doesn't compile/run.  I assume that this has something to do with the way that I have recently introduced a Feedback Node into the very bottom part of the Simulation Frame.  I am trying to get the program to initialise with a 100 tonnes value (Preset hopper with 100 tonnes) and to then subsequently calculate updated values.  I just cannot seem to get this working properly.  Any help would be greatly appreciated.

[Todd_Lesher]

I was about to break this VI into smaller pieces for debug, but there is an issue with the Simulation license on this PC. Copy-save and strip stuff out until it makes sense - then add things back in.

[0utlaw]

Hello Bunnykins,

I saw the same values as Todd in the initial VI you posted, the newer version does have all of the step size parameters set to "1".

With regards to the new VI, it appears to compile and run normally on my side (except for the missing data file.) Could you elaborate on the problems/errors you're seeing when attempting to run the VI?

Regards,

[bunnykins]

The error that I am receiving is as follows:

Error list

VI errors

Control & Simulation Loop 'Control & Simulation Loop': VI failed to compile

Details

An error occurred in compiling this VI

Not much to go on? I do not know what the problem is.

[bunnykins]

The problem that I'm having must be with respect to the Feedback Node.  If I take the Feedback Node out and wire a simple constant to the Selection Function (False) input then the program compiles and runs ok.  When I then put the Feedback Node in (as per my previously attached VI), then the program fails to compile/run with the same error message that I reported above.

Any ideas about this problem?

[0utlaw]

Hello Bunnykins,

I double-checked the source version of the VI you provided and realized that it was built in LabVIEW/CD&Sim 2010 - with that information, I found that the problem you are seeing was reported in the 2010 known issues document located here:

LabVIEW 2010 Control Design and Simulation Module Known Issues

http://www.ni.com/white-paper/11878/en

Under Corrective Action Request (CAR) #201449.  It appears that this issue was fixed in the 2012 release, which is why your code compiles and runs successfully on my end.  It also appears that the fix included a significant change in how the node itself works- in 2012+ the node will only "fire" on accepted time steps, meaning that the garbage data mentioned in the 2010 known issues list won't be a problem.

If you are unable to upgrade to a newer release of the development environment, the workaround described in the linked document (using the CD&Sim memory block) should give you the same functionality.

Regards,