I am running a system with GigE camera with NI framegrabber in continuous acquisition mode - in which I change some attributes every now and then.
So far I have been using following scheme to assert I am getting correct image after attribute change:
change attribute read "Last buffer number" property -> n run IMAQdx get image.vi set to "buffer' and parameter n+2 (+2 being due to the fact that i assumed attribute change arrives to camere during running exposure that will be unaffected by attribute change - hence i needed to discard "next" buffer) Unfortunately I still every now and then acquired image that obviously was aquired with previous attributes (e.g. I've dramatically increased.decreased exposure rate, while acquired image was very similar to previously acquired one). Guessing that it may have something to do with buffers I have increased "magic number" from +2 to +3. It indeed helped, but after longer usage I have discovered, that it only reduced the frequency of the error.
Hence I needed to design more "bulletproof" solution that will satisfy my timing requirements (stoping and starting acquisition is out of question as it takes more than 100ms what is unacceptable for me)
I would like to:
change attribute acquire information from camera that will allow me to fetch image acquired with changed attribute For such purpose I have discovered IMAQdx events - especially "Attribute updated" and "frameDone". Unfortunately, I could not find any detailed documentation about those functions. Therefore I would like to ask you for help to determine when 'Attribute updated" is triggered. Is it when:
driver receives the command and pushes it to camera? (pretty useless for me as I cannot relate it to any particular exposure) camera confirms getting it (then assuming it arrives during an ongoing exposure, I'll discard "next' image and expect second next to be correct camera confirms applying it (then I assume that next image should be obtained with correct settings) camera confirms it managed to acquire a frame with new parameter (pretty unlikely scenario - but the i'd expect correct image to reside in "last" buffer) Could you help me determine which case is true? Also should I be concerned about the fact that there may be a frame "in transition" between camera and IMAQdx driver which will desynchronize my efforts here?
I searched within this site and via Google for any related queries. Couldn't find any. Hence this post...
Example of Situation:
I configured an I8 Numeric with non-default limits in its 'Properties >> Data Entry' window...
Minimum of -2 (coerced); Maximum of 2 (coerced). I set up a simple event that looks for 'Value Change' of this Numeric.
No matter what the 'Increment' value and 'Response to value outside limits' are set to, the 'Value Change' must NOT trigger if the numeric is already at the limit and cannot be changed further. To explain, If current value of Numeric is 2 and I try to increment it, its value must remain at 2 and no event should be triggered. Similarly, with current value of Numeric at -2, if I try to decrement it, its value must remain at -2 and no event should be triggered.
What I found was that the value does remain at the limit, but an event is still triggered when the 'Increment' setting is non-zero. Is this normal behavior?
Test Numeric Event Triggering.vi coded in LV2014
I have been trying to understand what's going on with my tree control and I'd like to share this with the community to see if somebody has seen this behavior before. Maybe there is something obvious that I am not seeing...
I attached the VI (LV2011) with instructions inside (will take you 20s to perform the experiment, I dismantled the VI to its bare minimum). Please don't comment on the overall architecture (state machine...) since I modified the VI just for the sake of posting it here and removed all advanced features.
Long story short, after programmatically modifying the value of the tree, I modify its value a second time by clicking directly on one of the tree items. I then expect the NewVal value given through the left node of the value change event case to match the value of the tree terminal. Depending on the code that first modified the value programmatically, sometimes this expectation is met and sometimes it isn't. Run the code, it's easier to understand that way...
Thanks for your feedback!
Tree value issue.vi
new to Lava, so (kindly) let me know if I screwed up my post
I have a multi-user web application controlled by a LV web service. I keep track of all the users through the web service > sessions VI's. This is pretty cool and works really great. I can give each user different levels of authentication, force them to use SSL, track where they go and when throughout the website, etc.
Now what I'd like to do is keep track of when their session expires. Obviously I can provide a "Logout" link on the client-side which ultimately calls the "Destroy Session" VI, but I can't ensure that all clients will click the link to log out (e.g. how many times do you really sign out of gmail verse just close the browser?!)
What's the best way to catch the session timeout event that is specified during "Create Session" VI? It appears as if I need a "LV Web Service Request" object to even call the Destroy Session VI, which makes matters much more difficult it seems. Is this even possible?
Thanks for the help
Any thoughts on the simplest way to trigger a LabVIEW event using an external script in Windows? I want to be able to poke my LabVIEW application and kick off a predefined code block. No need to pass any information/message.
I'm looking for something very passive, unlike, for example, a listening TCP socket.