While loop takes control of everything, i.e. stop a while loop

Hi everybody,
I have a problem with a while loop, which I don't manage to stop as it
takes control of everything.
So, the problem is the following.
I wrote a vi to control an Optical Spectrum Analyzer and I need it to
scan a trace every Ta seconds. The scan must start when the user
presses the button "Start datalogging!" and must stop when the user
presses the button "Stop datalogging!" (this button is configured as
"swith after pression").
The problem is, anyway, that after starting the datalogging operation,
the user interface becomes kinda inaccessible, the mouse pointer
assumes the "hand format" and you can't push any button (actually you
can't move the scroll bars either, nothing), but the one to abort the
execution, making thus impossible to stop the acquisition or any other
operation.
It seems like the operation of collecting data is so "CPU consuming"
that LABVIEW can't "listen" to any input.
The LABVIEW version I am using is the 8.5.1.
I hope somebody can help me solving this problem.
Thanks a lot,
Gianluca

Hi,
You may want to try the following:
1) create a while loop, leave the conditional terminal open for now
2) inside the while loop, create an event structure (on the same palette as 'while'- and 'for' loops)
3) Add an event by right-cllicking the top textfield of the event structure, choose your startbutton-control in the left menu, and in the right menu scroll down to 'value change'. Before exiting this menu make sure to uncheck the checkbox for 'lock front panel'
4 inside the eventstructure for your start-button, put your start-button control - it needs to be read by the program to work properly (unless you chose another form of mechanical action). Wire it through the wall of the event-structure and to the conditional terminal, insert a boolean 'not' to reverse the polarity.
5) Add a constant to the 'timeout' value on the left upper corner (outside the event structure),give it the value 100 [ms]
6) select the timeout page in the structure (it was there by default as the first page)
7) insert your scanning program in here, it will iterate (start) every 100ms (due to your constant in step 5)
8) add another event, select your stop button control in the left menu, select 'value change' in the right menu
9) Place your stop-button control inside the new page in the event-structure, wire a line through the frame down to the conditional terminal
10) you are done
Brgds
T

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Closed loop velocity control based on load cell force

Hello,
My application is for a drill, that drills into rocks of various densities for the purpose of collecting rock core samples.
My setup has 2 motors which get controlled, one spins the drill bit at a constant velocity, the other moves the drill mechanism along a Z axis.
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1. Your hardware and software look appropriate assuming the motors are compatible with the 9505s. You didn't mention the NI SoftMotion module in your software list which is something you will need.
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If you do need trajectory generation, you would want to keep most of the example code the way that it is, but then program in a 'Force Mode' that utilizes the force and velocity controly as described above. You could think of it as having two different routines programmed side by side.
Regards,
Burt S

Stopping a while loop using the time difference of two tick counts

Hi Guys,
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However, when I tried to run the code, the program just didn't run. Hence I created a similar program which puts the last tick count in new frame sequence. When I ran this code, the program never stopped.
Do you guys have any idea what went wrong with my codes.
Thank you!
Erry
Solved!
Go to Solution.
Attachments:
1. Tick Count.vi ‏27 KB
tickcoun2.vi ‏27 KB

Dataflow!
In both VI's the stop terminal of the while loop is controlled by a boolean whose source is ouside of the while loop. So that loop will either run once, or run forever, depending on the value of the boolean that is calculated before the loop starts and shows up at the tunnel going into the loop.
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14. Once my photos look the way I want, I then export them to JPEG. I have set up a Photoshop droplet for Lightroom that will then do all my sharpening after export.
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Thanks to Tony Long for his suggestion in this thread, which caused me to go on a search for the optimal Lightroom/Capture workflow: http://www.adobeforums.com/cgi-bin/webx?7@@.3bc719df/3
If you are interested in taking a look at the final output of the workflow listed above, please look here: http://photos.unsavory.com/p634883589
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The Seller should have performed these Steps Before you took possion of the Device.
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salm4n wrote:
I have bought a used ipad mini 2
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Stop dependant while loops with 1 button

Hi,
I am developing a utility that allows a user to configure up to 2 devices (both use same driver with a different board number), click initialize, which then brings up a file dialog and displays arrays for the data to be collected and some error messages for each measurement. The user then clicks the Start/Stop button to begin collecting and logging data. Currently i have a Wait(ms) block to allow the user to set often the measurement should be made. Currently the Start/Stop button allows collection to be started, paused, and started again. My problem is trying to have a master stop button that should stop all loops immediately when it is pressed.
I tried using a global variable for the stop button, but the measurement and logging while loop doesnt stop until after the wait(ms) block times out. Can anyone give suggestions. If i need to restructure the VI into different loops, I can do that. I just want to understand the right way to program something like this.
The VIs are attached. I removed the device specific measurement VI so that anyone can open the vis and run them to see how it works.
Attachments:
2Devices_withoutMeasurementVI.vi ‏112 KB
BuildOutput.vi ‏27 KB
stopGlobal.vi ‏5 KB

Ok. I had a chance to take a look at your code and I think you don't quite understand the concept of "dataflow". Let me see if I can help.
First of all...when I refer to your upper structure, I am referring to the first while loop, sequence structure, and subsequent while loops. When I refer to your lower structure, I am referring to the while loop containing the event structure. Just so we get our terminology straight.
I believe that you are under the illusion that your upper structure contains three parallel while loops. It does not. It contains three SERIAL while loops. There is dataflow dependency between the while loops. The sequence structure requires data that is not available until the first while loop has finished executing, so the sequence structure cannot start executing until the first while loop has terminated.
The second while loop requires inputs from the first frame of the sequence structure (which, by the way, you don't need and should get rid of...the sequence structure, I mean), so it cannot start executing until the first frame of the sequence structure has terminated. The third while loop requires inputs from the second while loop...so, again, the third while loop cannot run until the second while loop has finished executing.
Now, for your stop button. You have that global stopping all three loops. So here's what is happening in your program:
Your program starts. The first while loop executes in parallel with the loop which contains the event structure.
At some point you press the "stop" button. Both the first while loop and the loop containing the event structure finish executing.
The first frame of your sequence structure executes.
The second frame of your sequence structure executes. The second while loop reads the "stop" value from the global, so it executes once and then finishes.
The third while loop starts executing. Again, the loop reads the "stop" value from the global, so it executes once and then finishes.
Then your program terminates.
You need to restructure your program, because right now it doesn't make any sense at all. Your block diagram would benefit from some serious tidying up as well, your wiring is a mess. I suggest you look into a state machine architecture for this program.

What would be the simplest way to view and take control over the internet?

Hi All:
Can some one tell me what would be the best and simplest way to connect from my laptop to another laptop through the internet?
I have DYNdns running on the second laptop and have a host name assigned to that system for it to update the IP since the system uses different internet connections. The services that I would like to be able to have are the viewing and controlling of the system. I've read some where in this NG that if I have a copy of ARD admin. installed on that system also, it would be one way to do it... can some one verify this and please let me know if there are any specific settings I need to have on either one of the systems.
I can connect to the second laptop while in my home network with no problem and perform all tasks. when trying to connect through the internet.. the system shows offline .
Both systems are identical in hardware an software, Intel 2.16, 2G's RAM, OS X ver 10.5.2 all up to date and ARD 3.2
Yes, I'm new to ARD and yes I'm searching the NG and the net. but I figure it doesn't hurt to ask since time is limited.
All help greatly appreciated ..
TIA
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To be able to connect to a workstation from outside it's network, the ports that ARD uses must be open on both ends of the connection. ARD uses ports 3283 and 5900 so those must be open.
If your workstations get their addresses from an NAT device rather than being "real", the ports also need to be forwarded in the router to the workstation's internal IP address. ARD uses port 3283 for the reporting and updating function, so if your Macs are getting their IP addresses through NAT, since you can only forward a port to a single workstation, you can only get reports, push package/files to etc. for a single workstation.
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Code golf: stop two while loops with guaranteed iteration ratio

Proposal
In the vein of the Perl tradition, I'd like to see if there's any interest in solving short programming puzzles in LabVIEW. Anyone can post a problem and define the rules for solving it.
Here's a beginning/intermediate question to whet your "palette".
Description
With one user-action, how would you stop two while loops such that the ratio of their iterations is the always the same? One concrete way to visualize this situation is in taking measurements: two instruments use the same timing source to take measurements, but second divides the clock down so that it is an integer factor slower than the first. For example, if the slower instrument is four times slower, then at the end of the VI, if the slower instrument takes 100 measurements, the faster instrument has taken 400.
Rules
You may only use vi.lib
You cannot include any other subVIs
Your solution must pass for loop1 interval as low as 25 ms
Template (attached in LabVIEW 2009)
If folks are interested in this, then let's figure out how to make future problems better. Please post your suggestions and critiques, but only if you also post a submission ;-)
Solved!
Go to Solution.
Attachments:
Multirate Loop Code Golf.vi ‏11 KB

Norbert_B wrote:
a) You work with an integer factor of speed. While this matches many application areas, there are still cases where the factor has to be floating point (e.g. 2.5). Additionally, the factor might "invert", so the master loop runs slower than the slave (factor 0.5 for instance).
It sounds like you're about to post another code golf question. If you think the problem scope is too small, you're welcome to fashion one to your taste. Thanks for volunteering :-D
Norbert_B wrote:
b) This example does not take into account that the hardware has to be synchronized with more accuracy than the software supplies (PXI?). If hardware synchronization is required, there are two possible ways:
- The factor can be included in the synchronization (using PLL for instance)
- The factor has to be software implemented by data reduction for the task running at the lower pace.
Hrm, maybe puzzles aren't really your thing after all. You are correct: I did not define every constraint that can lead to a provable best closed-form solution, but that does not prevent people from stating their assumptions and forming creative, well-reasoned, and still correct designs. I overlooked this reading of the description and neglected to add a statement that said solvers were free to add their own conditions. I will do so in the fugure :-)
If we choose the first of your suggestions, the VI must still retrieve the data at different rates. You can dedicate a loop for each instrument to decouple any jitter and latency introduced by their connectivity or internal operation; this adds some margin of safety when there is thread and driver contention. You can also implement a single counting loop like altenbach and forego the multiloop complexity.
Norbert_B wrote:
c) You don't state anything about "what happens with the data". Is this time consuming? Does it introduce additional delay in loop iterations? Is it OK to have data loss?
I don't know -- you decide, you disclose, and you solve :-)
In my specific situation, the measurements are time consuming and do add delay (each data "sample" is 5-20 megabytes), none can be lost, and the data must be available for others to analyze later. In addition, the amount of data is saturating the hard disk throughput. If a particular write takes too long, the instrument driver may overwrite a yet unfetched sample, which is unacceptable. I did not add these details to the problem discripton becuase they don't impact the puzzle.
I don't want to burden people with my situation and ask them to solve my problem: I want to encourage them to bring their intuition and experience to a discussion. This is the design process at its heart: understanding why and how constraints affect your decisions. If a person states the additional conditions they've assumed, readers can learn why, and more importantly, when a Notifier might be more desirable than an Occurance or a Queue more robust than a Data Value Reference.
The best NI-published advice for stopping multiple while loops (https://www.google.com/search?q=labview+stop+multiple+while+loops) is laughable (and is the "solution" in my template).
Would you care to re-approach and contribute to this puzzle? I suspect you have a lot to offer :-)

Stopping a while loop inside a while loop

Hello,
I have a while loop which is inside a while loop which houses my enetire application, When stopping the inner while loop portions of my outer loop stop working, How do I setup the inner while stop that it will not interfeer with the outer while loop?
Thanks,
Gil,

It sounds like he is using a simple archetecture. But switching to a different archetecture may not be necessary. Simply because it doesn't work, doesn't mean scrap the whole thing and start over. He's got a bug and needs to fix it. Is it the best archetecture to use, absolutely not, but simple or general archetectures can be effective based on the application.
Post your VI so we can take a look and give you some pointers and suggestions for improvement.
Reese, (former CLAD, future CLD)
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The first method takes frame grabbing control of your player which you have already created from the datasource of the camera and it grabs a frame, returns it as a buffer, then calls the second methos which converts the buffer to an image.
It is very straight forward and I was kicking myself when I figured you could do it this way - I had been weeks playing around with the player and processor from one datasource.
hope this helps!

Take control of VPN Client

Dear All,
someone can tell me if is possible take control of the remote client connected by VPN, through application like Remote Desktop or NetSupport?
We use a VPN Concentrator and one of our customer need to take control of the client-desktop that connected by VPN.
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Control does not stay in case structure while using motion VIs

Hi,
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Regards,
Giridhar Rajan
Automation Engineer,
Cruiser Controls,
Mumbai, India

Hi,
Our motion controllers allow you to preemptively start a move in the middle of a current move. For example if you are moving from point A to B and based on some logic, you determine you need to immediately start moving to point C. A preemptive move allows you to just load the new target position and call start. You do NOT have to first stop the current move and then start the new move.
In your case, you want the first move to complete before the second move starts. There are two ways to handle this. First, wait for the move to complete via a Wait For Move Complete function/VI call, or use the Check For Move Complete function/VI in a loop. Second, use Blend Start instead of the regular start. A Blend Start (if blend factor is set to 0) waits for the first move to complete before the second move starts.
Check out the help topics for Start Motion and Blend Motion to learn more.
Thanks,
Rodger S.

Failing to take control of navigation

Hi,
Im trying to take control of the navigation. Im using MyFaces.
let me explain:
I wish to have my own piece of code to parse the request URI and control the navigation to the next JSF page.
This functionality is desired for accomplishing a permalinks scheme of some sort.
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The link root/yuval/yuvals_stuff should cause the following to happen:
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- I use a ViewHandler to load the data (it delegates the call to some service that gets the data from the database)
- I now forward the user to a known jsf page that is bounded with the viehandler and presents yuval's stuff .
Actually, the first time i try to use the code, the navigation goes well. But right after refresh or calling the same url again I get an exception. The code and the exception are provided here:
Here is what i do inside a servlet filter (I also tried to put this code inside the faces servlet, just for testing):
<code>
FacesContext fc = FacesUtils.getFacesContext(req, res);
String action = "#{viewPollViewHandler.go2}";
javax.faces.application.Application application = fc.getApplication();
MethodBinding mb = application.createMethodBinding("#{viewPollViewHandler.go2}",null);
String outcome = (String)mb.invoke(fc, null);
String fromAction = mb.getExpressionString();
NavigationHandler navigationHandler = application.getNavigationHandler();
navigationHandler.handleNavigation(fc, fromAction, outcome);
String viewId = fc.getViewRoot().getViewId();
UIViewRoot view = fc.getApplication().getViewHandler().createView(fc, viewId);
view.setViewId(viewId);
fc.setViewRoot(view);
fc.getExternalContext().dispatch(viewId);
fc.responseComplete();
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Explanation:
First we try to get the FacesContext, using the current request and response objects. Now we know what action we want to invoke on what ViewHandler, so we go ahead and make a method binding for this method through the JSF Application context. Now we invoke the method and get the outcome String from it. Till now everything seems to work ok � we get the ViewHandler's method invoked correctly and we get the proper outcome String from it.
This means the ViewHandler is now populated with our needed data, so all we have left to do is go to the presentation page that uses this ViewHandler.
We use JSF's NavigationHandler to navigate as usual, giving it a "fromAction" and an outcome. Now we want the name of the page for this navigation, so we get the view id from the FacesContext. The view id is correct and points to the next page as states in the faces-navigation.xml, so we set it as the new view root and try to "dispatch()" (which is the same as "forward()") to it.
The result seems sufficient, as we get to the next page and all the data is presented correctly (sometimes, in IE only we experienced some javascript errors that were unknown). The big problem occurs when trying to hit "REFRESH" or clicking back and then trying the original href link again. We suddenly get a NullPointerException that occurred in the "getValue()" method of JSF's getValueBinding()".
Can anyone contribute?
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Yuval.

Hey all,
The following link shows how to solve the problem:
http://wiki.apache.org/myfaces/InvokingJsfPagesWithStandardUrls#head-6c1aaf488d48f938896da962aaa4361ec3ffaf70

Labview Loop Takes 100% cpu

Hello,
I'm wondering the best way to send a serial command when a button is pressed. Right now I have a while loop that checks if the button is pressed each time. If is is, it sends the serial command and adds the response to a text box via a shift register. If not, the original text box info is passed to the shift register. However, this loop takes 100% cpu (ok, only one core at 100% so technically %50), and I think its because the text box is getting overwriten every cycle. However, I'm not sure how else to do it. Attached is a print screen, let me know if you would like the file.
Thanks,
Eric
Solved!
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An event structure is the best way. The next best way is to simply put in a wait in the loop.
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While loop takes control of everything​, i.e. stop a while loop

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While loop takes control of everything, i.e. stop a while loop