How to start/stop 2 parallel while loops

My question might be simple to answer for experts, but as a Labview beginner would be great to receive your help:
I hav a VI with two parallel while loops. The first loop runs in a tact of 100 ms to aquire voltage, speed and to output a speed setpoint for a motor in the same tact, read from a table.
Finally all values are written to a log-file.
The question: As soon as I run my VI, data logging starts too and my motor runs. How can I implement a button to start all loops parallel, and how can they be parallel be stopped too if I want to stop measurement? Tryed to set a local variable for both stop buttons but it didn´t work.
Thanx to all, Markus
Attachments:
screenshot.JPG ‏74 KB
Measure and log data.vi ‏147 KB

SnowMule wrote:
Starting the two is easy; use the error cluster to enforce dataflow.
Stopping them is a little trickier; the code you have now isn't very expandable so I'd recommend finding a different architecture. A notifier functions like a queue with a size of 1, a queue works well for sending commands/data between loops.
There is one other significant difference between queues and notifiers. A queue can only have one reader. If you have multiple readers of a queue who reads it will be random. A notifier can have multiple listeners. It fact, that is it's purpose.
Mark Yedinak
"Does anyone know where the love of God goes when the waves turn the minutes to hours?"
Wreck of the Edmund Fitzgerald - Gordon Lightfoot

Similar Messages

How do i stop a while loop

I'm new to labview and I'm having a problem stopping a while loop (running windows XP/2000 with the student edition of labview express 7).
I'm doing a data acquisition program where I'm constantly reading in voltage and comparing it to a set point value, when the input voltage goes above the set point, i want the while loop to stop. How do I do this? I already have an LED going on when the criteria is met, but I'm not sure how to actually stop the loop (i.e. change the iteration value from true to false-i guess). If anyone can please assist me with this I would very much appreciate it.
I've included my program too.
Attachments:
CO_Detection_Monitoring_System_Modified.vi ‏60 KB

Hello Everyone-
I've just posted a message about stopping a while loop and it was answered accurately and quickly- thanks to LV_Pro and PauloM- thanks much- its nice too see that there are many helpful people out there! Unfortunately, I have 2 more questions to ask of the forum.
My application is almost completed- I just need to add an elapsed time counter that will tell me how long it took for my LED to trigger (from my set point-i.e. when from 0:00:00 until when my loop stopped).
Now I've found a perfect elapsed time counter on the NI web site contributed from Mike Hall from Ohmeda Medical- the page is here.... http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=D37E2493DC333076E034080020E74861&p_node=DZ52032&p_source=external
So my first question is, it looks like I can just extend the while loop box in my 'CO detector... .vi' and paste just the code from the 'elapsed time.vi' while loop into my loop and I will be set- but do I need to change my wait until next multiple to be a 1000 too in my program? Probably, but I'm not sure hence the question- or other ideas would appreciated.
My second question is now that my application is complete (after I add the elapsed time above), I need to exactly duplicate this process for 7 other DAQ inputs (i.e. right now I'm using only 1 of 8 analog inputs on the FP-AI110). So should I make my 'CO detector.. .vi' a separate program (I remember reading something about this in one of the posts earlier).
Any help is very appreciated.
Thank you again,
Daniel
Attachments:
CO_Detection_Monitoring_System_Modified.vi ‏60 KB

Starting stopping multiple while loops

I have a rather large VI that runs multiple while loops with case strutures inside.
I would like to be able to shut off and on the while loops programmatically depending on events.(cycle complete or cycle started)
I need to store my measured data in a table but everytime I shut off the while loop the data I gathered is lost.
So it goes like this- measure analog voltage-put it in a numeric indicator...now I want to put in a table only once per cycle of my machine.
If the opeator pushes the reset button the table is available for a report generation acquisition.
Any help would be appreciated.
Thanks
Solved!
Go to Solution.

Do you want something like this?
Attachments:
Loop_Control_Multi.vi ‏109 KB
Loop_Control_Multi_Demo.vi ‏177 KB

Stop multiple while loops in Vision Aquisition

Hi, I want to close multiple while loops with one stop button. I'm using the Vision Acquisition software for recording from multiple cameras and I want to close this recording from all cameras simultaneously. Since I'm knew to LABView I don't know how to do this. I'll include my VI here and maybe someone can help me. Thanks!
Solved!
Go to Solution.
Attachments:
Aquire Images 2 with Cameras.vi ‏410 KB

A local variable should be enough for your implementation. Look at the following article:
Stopping Parallel While Loops in LabVIEW With One Stop Button
Adnan Zafar
Certified LabVIEW Architect
Coleman Technologies

How do i exit a while loop using event handler

Hello,
I have an event handler structure within which i run a while loop for a particular event. I would like to interrupt the execution of this while loop as soon as another event occurs, even if the while loop has not finished execution. I have tried so many ways, the best i could get is exiting one itteration after the new event occurs which is no good for me.
Any suggestions???
Thanks
Me

Instead of having a task while loop in an event case, put your task while loop in parallel with the loop surrounding the event structure. When the event which should start the task occurs, you can signal the start of the task while loop. You could use local variables of references to start/stop the loop when an event occurs. You could also use notifiers instead of variables to pass signals to start/stop the while loop. In general you should have a while loop for the event structure, and a parallel while loop to do the tasks. The parallel loop is controlled by variables or notifiers which are set in the event cases.
- tbob
Inventor of the WORM Global

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 :-)

How to code a parallel 'for loop' and 'while loop' where the while loop cannot terminate until the for loop has finished?? (queues also present)

I've attached a sample VI that I just cannot figure out how to get working the way that I want. I've labeled the some sections with black-on-yellow text boxes for clarity during the description that follows in the next few sentences. Here's what I want:
1) overall -- i'm intend for this to be a subVI that will do data acquisition and write the data to a file. I want it to use a producer/consumer approach. The producer construct is the 'parallel for loop' that runs an exact number of times depending on user input (which will come from the mainVI that is not included). For now I've wired a 1-D array w/ 2 elements as a test case. During the producer loop, the data is acquired and put into a queue to be delt with in the consumer loop (for now, i just add a random number to the queue).
2) the consumer construct is the 'parallel while loop'. It will dequeue elements and write them to a file. I want this to keep running continuously and parallel until two conditions are met.
      i. the for loop has finished execution
      ii. the queue is empty.
   when the conditions are met, the while loop will exit, close the queue, and the subVI will finish. (and return stuff to mainVI that i can deal with on my own)
Here's the problems.
1) in the "parallel for loop" I have a flat sequence structure.. I haven't had time to incorporate some data dependency into these two sequential sections, but basically, I just care that the "inner while loop" condition is met before the data is collected and queued. I think I can do this on my own, but if you have suggestions, I'm interested.
2) I can easily get the outer for and while loops to run sequentially, but I want them to run in parallel. My reasoning for this is that that I anticipate the two tasks taking very different amounts of time. .. basically, I want the while loop to just keep polling the queue to get everything out of it (or I suppose I could somehow use notifiers - suggestions welcome)... the thing is, this loop will probably run faster than the for loop, so just checking to see that the queue is empty will not work... I need to meet the additional condition that nothing else will be placed in the queue - and this condition is met when the for loop is complete. basically, I just can't figure out how to do this.
3) for now, I've placed a simple stop button in the 'parallel while loop', but I must be missing something fundamental here, because the stop button is totally unresponsive. i.e. - when I press it, it stays depressed, and nothing happens.
suggestions are totally welcome!
thanks,
-Z
Attachments:
daq01v1.vi ‏59 KB

I'd actually like to add a little more, since I thought about it a bit and I'm still not quite certain I understand the sequence of events...
altenbach wrote:
zskillz wrote:
So i read a bit more about the 'dequeue element' function, and as I understand it, since there is no timeout wired to the dequeue element function, it will wait forever, thus the race condition I suggested above can never happen!
Yes, you got it!
As I've thought about it a bit more, there's a few things that surprise me... first, the reason the 'dequeue element while loop' errors is not because there's nothing in the queue, it's becaues the queue has been released and it's trying to access that released queue... However the problem I have is this --- Even though there's no timeout wired to the dequeue element, I still would think that the while loop that contains it would continue to run at whatever pace it wanted -- and as i said before.. most of the time, it would find that there is nothing to dequeue, but once in a while, something is there. however, it seems that this loop only runs when something has been enqueued. the reason I say this is illustrated in the next code sample MODv2 that's attached below. I've added a stop button to the "queue size while loop" so the program runs until that is pressed. I've also added a simple conditional in the "dequeue while loop" that generates a random number if it a button is pressed... but this button is totally non-responsive... which means to me that the "dequeue while loop" isn't actually continuously running, but only when an element is added to the queue. this still seems almost like the 'dequeue while loop" waits for a notifier from the queue telling it to run. can you explain this to me? because it is different from what I expect to be happening.
rasputin wrote:
I tried to open your VIs but it doesn't work. LV
is launched, the dialog box (new, open, configure...) opens and then...
nothing. Not even an error message. I guess it isn't a problem of LV
version or a dialog box would appear saying this. Could you, please,
send a image of the code?
Thanks,
Hi Rasputin, I'm using LV8. I assume that was your problem, but who knows. I've attached a pic of of altenbach's solution since it's what I needed.
thanks
-Z
Message Edited by zskillz on 10-20-2006 11:49 AM
Attachments:
daq01v1MODv2.vi ‏63 KB
daq01v1MODpic.JPG ‏116 KB

I have a for loop inside of while loop.when i press stop for while loop, i also would like to stop for loop.how can i solve this problem?thanks

i have a for loop inside of while loop.when i press stop for while loop, i also would like to stop for loop.how can i solve this problem?thanks

Hi fais,
Following through with what JB suggested. The steps involved in replacing the inner for loop with a while loop are outlined below.
You can replace the inner for loop with a while by doing the following.
1) Right-click of the for loop and select "Repalce" then navigate to the "while loop".
2) Make sure the tunnels you where indexing on with the for loop are still indexing.
3) Drop an "array size" node on your diagram. Wire the array that determines the number of iterations your for loop executes into this "array size".
4) Wire the output of the array size into the new while loop.
5) Set the condition terminal to "stop if true".
6)Drop an "OR" gate inside the while loop and wire its output to the while loops condition terminal.
7) C
reate a local of the boolean "stop" button, and wire it into one of the inputs of your OR gate. This will allow you to stop the inner loop.
8) Drop a "less than" node inside the inner while loop.
9) Wire your iteration count into the bottom input of the "less than".
10) Wire the count (see step 4 above) into the top input of the less than. This will stop the inner loop when ever the inner loop has processed the last element of your array.
Provided I have not mixed up my tops and bottoms this should accomplish the replacement.
I will let others explain how to takle this task using the "case solution".
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

How to stop a while loop of event structure from a main vi

Hello;
sorry for my english
I have to stop a subvi from my main vi, the subvi contains a while loop and an event structure so I need to stop this loop while directly from my main vi I have tried global variable but it did not work
any help please or example !!!
Solved!
Go to Solution.
Attachments:
stop a while loop and event structure from main vi.png ‏16 KB

IYED wrote:
Hello;
sorry for my english
I have to stop a subvi from my main vi, the subvi contains a while loop and an event structure so I need to stop this loop while directly from my main vi I have tried global variable but it did not work
any help please or example !!!
If this is an example of how your code looks, I'd clean it up before the developer who has to work on it next hits you over the head with his LabVIEW Style Book.
Bill
(Mid-Level minion.)
My support system ensures that I don't look totally incompetent.
Proud to say that I've progressed beyond knowing just enough to be dangerous. I now know enough to know that I have no clue about anything at all.

How to stop a while loop in LabVIEW from a C program

How to stop a while loop in LabVIEW from a C code

hi
I think by creating dll you can stop the while loop from your C program.For that you just create dll (Dynamic Link Library) for the VI which has that while loop.
Anyway can u please explain ur requirement clearly.

How to stop a while loop after certain time using Elapsed time vi

how to stop a while loop after certain time using Elapsed time vi.

Hi Frankie,
Just place the Elapsed Time VI inside the WHILE loop, and wire the 'Time Has Elapsed' output to the conditional terminal in the lower right corner (which should be set to 'stop if true' by default).
In the future, please post your LabVIEW questions to the LabVIEW Forum. You have a much better chance of getting your questions answered sooner, and those answers can then help others who are searching the LabVIEW forums. Thanks!
Justin M
National Instruments

How to stop a while loop which contains a timed loop

Hi,
I'm a new hand to labview, and I'm using labviw 7.1, NOT 8.x. I'm trying to do a measurement, in which the flow would look like the attached file (I have stipped all hardware related components to make it easy to read). My questions are:
1. In Loop 3, when the comparison (x>20.85) is true, Loop1, Loop2 and Loop3 are stopped, why it won't quit the while loop (I have wired it to while loop stop)?
2. When it is running, I click on stop button, why it won't stop?
Thanks!
Attachments:
SyncTimedLoop32.vi ‏228 KB

hwm wrote:
2. When it is running, I click on stop button, why it won't stop?
The stop button is read outside of the inner while loops. So the inner while loops will continue to run until their stop conditions are met.
hwm wrote:
1. In Loop 3, when the comparison (x>20.85) is true, Loop1, Loop2 and Loop3 are stopped, why it won't quit the while loop (I have wired it to while loop stop)?
It seemed to me like it would, but sometimes it seemed like I had to set change the numeric value one more time before it would. You have a very odd structure there by placing the event structre inside the while loop with the other loops. I think you may be running into issues where events are getting queued up in the event structure, or race conditions between when the event structure might execute relative to the other loops. It is all very odd and difficult to predict all the ways these structures might interact and relative timing. Usually event structures would belong in their own parallel while loop. I think you need to rethink exactly what you are trying to do here. It probably isn't event necessary to use the stop timed structure functions. A local variable or a notified to pass the "Stop status" from loop 3 to the other loops (or the separate event structure loop to the other 3) would probably be better.

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.

Problem with two parallel While loops

I have a serious problem with controlling two parallel While Loop. Here is the deal:
I have written a VI to send a series of commands called Cycle through Serial Port to a custom hardware. One of these commands is setting motor pressure by sending it's command and changing it's voltage. After setting desired pressure I have to read and control motor pressure, again through serial port in a parallel loop. There is a Pressure Sensor in system and I can obtain current's motor pressure by sending a command and receiving pressure value. In the first While loop I send some commands to hardware including Pressure Setting Command trough a state machine. In the second While Loop I read pressure value and then decide to increase motor voltage or decrease it. Now the problem is in communicating these two loops. In cycle after "Init" state when state reaches "Pressure 2 Bar" motor voltage will increase. Meanwhile I have to control this voltage in parallel While Loop. As you can see I used Local Variable to communicate between these two loops. The problem is that loops are not synchronized. Specially when I switch to "Pressure 3.8 Bar" state during cycle running control loop (second while) is still working based on "Pressure 2 Bar" state not 3.8 bar. Because of this motor pressure goes to 3.8 bar for a sec (becuase of "Pressure 3.8 Bar" state) and comes back to 2 bar (because the second while still has not gotten that new state,most probably cause of all the delays in the loop) and after couple seconds it goes back to 3.8 bar.
I really don’t know what to do. Is there a way to fix this? Or I should consider a better way to do this?
I went through Occurrence Palette but couldnt figure out how to embed that in the VI.
Sorry for my poor English. I attached VI and it's subVIs as a LLB file. I can explain more details if somebody wants.
Attachments:
QuickStartCycle.llb ‏197 KB

I make it a point to NEVER have a WAIT function inside a state machine.
It sort of defeats the purpose, which I define as "Examine current state; decide whether you've met the conditions to advance to another state, then get out".
For example, I have a single state machine VI controlling four identical instruments, via TCP connections.
For some functions, that means issuing a command, waiting 60 seconds, then reading results.
If I waited INSIDE the state machine, then it's tied up waiting on one device and cannot handle any others.
Not a good plan.
To handle this, I have a loop which calls the state machine. After issuing the command, the state goes to "Waiting on Response", and there is a target time of 60 seconds from now.
It's called over and over in that state, and each time merely compares NOW to the target time. If NOW is past the target, then we read the results.
the state machine can tell the caller when to call back; that's how I distinguish between an urgent need and nothing-to-do.
By having the CALLER do the waiting, instead of the state machine itself, the state machine is free to handle another device, or do something else on the same device.
You should be calling the state machine over and over and over anyway. So, have the state machine "control the pressure" on every call, and THEN examine whatever state it's in.
Steve Bird
Culverson Software - Elegant software that is a pleasure to use.
Culverson.com
Blog for (mostly LabVIEW) programmers: Tips And Tricks

How to out from infinite while loop in sub VI

Dear Sir,
how to out from infinite while loop in sub VI from main VI
attached photo for solution but I can't understand it and i can't find the function in photo
please help
Attachments:
stop_subVI_frm_main.JPG ‏36 KB

Asking how to get out of an infinite loop is like asking how to find the end of a circle. I'm not trying to be sarcastic but by definition, if there is a way out of the loop, then it is not infinite. I think what you are asking is how to avoid creating an infinite loop. Is there something about the suggestions you have been given that you do not like? My favorite suggestion is the notifier but maybe you just need an example. Turn on context help and read about the notifier functions in the code below.
This is your top level VI
And this is your subVI
If this seems too complex then a global variable will work too. But what seems simpler can cause much more complex bugs. You can code fast and spend lots of time debugging or you can code slow and spend less time debugging. Personally I perfer writing productive code than looking for bugs any time.
=====================
LabVIEW 2012

How to start/stop 2 parallel while loops

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