LabVIEW RT Remote Panel Problem on FP-20XX

[tbutterfieldeng]

String indicators do not hold their value on a remote LabVIEW RT panel. A value that is written to a string indicator will only be displayed once in the indicator and will be empty from that point on.

[JeffBoettcher]

Front panel indicators, on remote panels or not, update when a value is written to the front panel terminal in the code. They can also change when a different value is written to a property node or local variable in the code, though there are issues with this under RT due to the fundamental separation of front panel from code. Likely somewhere in your code is writing an empty string to the indicator on a subsequent loop iteration after writing your actual data. You would need to either write the desired data every loop iteration, or better yet, put a case around the front panel terminal so that it only gets written to when you explicitly change the string.

[beatz]

This seems to be related to my problem.

In my application (running on a RT-target) different measurement task are split up in SubVIs. The SubVIs are called if the respective measurement mode is activated by the user and run as long as it takes to complete the task. The result of these measurement task are datafiles and graphs on the front panels of these SubVIs.

The Problem is that on some of these SubVIs the graphs and other elements contain old data if the respective VI was not displayed during runtime and viewed afterwards trough the remote panel browser plugin. On other SubVIs this problem did not occur...

There seems to be a difference if the indicator is gets its data trough a local variable or its terminal... If data is only written to the terminal the indicator is only updated if it is displayed somwhere. If the data is written to the local variable the indicator displays the right value even after the subvi has already finished.

Is this somwhere explained? it still looks strange to me

Regards, Beat ZAHND

[Russell_G.]

Hi Beat

I have a few questions that may help narrow down what may be causing this issue.

Are these subvi's in your application set to "Show front panel when called"? Is this problem only exhibited with the subvi's? Or is it with other indicators in your program?
Is this behavior exhibited when you target your RT controller? Or is it just when you have an executable on the RT controller and are viewing the front panel through a web browser?
What version of LabVIEW are you using?

[beatz]

It seems I was wrong. Not the data was old but the graph axes where wrong. I set the scale offsets and multipliers programmatically using property nodes. If the subVI frontpanel is displayed in the browser while the property nodes are called the scales ar set as expected. If the panel is oppened at a later time or the reload button of the web browser is pressed the scales jump back to what has been set as default in the properties of the graph.

- "Show front panel when called" has no effect on this

- Our application has indicators only in subvis. The main VI is controlled by commands from a TCP/IP socket and has no controls or indicators on its frontpanel

- this behaveiour is with compiled executables and when launched from host laview

- labview is 7.1.1


Regards, Beat

[Russell_G.]

Hi Beat

In general, LabVIEW Real-Time does not support property nodes for deployed applications. But if you can post some simplified example code along with explicit instructions on how to duplicate the issue, I'll take a look at it.

[beatz]

Yes, I have seen this in the 6.1 RT release notes. But in the 7.1 release notes it was no more mentioned.

Here a standalone example of our VI. It is part of a main application which runs this subVI on user demand. The results are viewed with the remote panel during or after runtime of this VI.

Regards, Beat

[Russell_G.]

Hi Beat

Even though the LabVIEW 7.1 release notes fail to mention that property nodes are not generally supported in LabVIEW Real Time, this is still the case. Basically, you're remote front panel will ONLY be updated with your property node when the front panel is being viewed through the remote front panel or through the default communication. This KnowledgeBase explains in greater detail what is going on.

One thing you may want to consider implementing in your program is something like a "refresh" button on your front panel, which will then run your property node code to set the scale correctly on your graph while it is being viewed.