While loop termination...

So I have this long sequence of frames and I have an while loop which runs outside of the sequence. I want to to terminate the while loop after the last frame of the sequence has completed. I tried to wire a logic true constant from the last frame to the while loop but it does not work because the while loop seems to terminate prematurelly. Could someone sugguest a way of dealing with it? I can' figure out a solution for some reason.

Then the answer is, as with the other case, data dependency. If you wire a value out of your sequence frame into the while loop you've established a data dependency for the while loop since the while loop needs to know what the value of that wire is before it can execute, and the value is not set until the sequence frame ends.
Since your while loop houses an event structure, generate an event at the end of your sequence frame to stop this parallel loop. A crude solution: Wire a True value to the "Value (Signaling)" property of the "Stop" control, and change the event case from "Mouse Up" to "Value Change". You should make sure to initialize the "Stop" button to False at the start of your program, and to change the mechanical action to "Switch When Released":
Attachments:
Example_VI_BD6.png ‏6 KB

Similar Messages

Dsc periodic I/O "stop while loop" usage?

I'm using LabView 8.5.1 with DSC. I have created a working periodic I/O server VI and successfully deployed it.
The one glitch I am running into is what happens when the Shared Variable Engine I/O process is terminated. I normally terminate it by using "remove process" from Variable Manager.
The I/O server wizard lets me choose the while loop for termination during the build process, but any code following the while loop is not executed. In fact, the process continues running for 10 seconds until the "abort VI timeout" is reached, at which point the VI stops. The "stop" terminal of the main while loop is wired to a "create control" "STOP" button on the front panel. Publishing or not publishing the "STOP" control during the I/O wizard process has no effect.
I'd like to do cleanup steps after the while loop terminates. Unfortunately the "Heat Exchanger" example has no code after the while loop to illustrate the concept.
What am I missing?
Thanks,
Mike

Hi Van - let me clarify my question...
I don't believe that the termination portion of the DSC "periodic I/O server wizard" actually works properly, or at least an example is needed of how to make it work.
It appears to me that the wizard functionality of "choosing the server termination method" might not work. Within the wizard, the two options are to abort the running server VI, or to choose a "while loop" to be forcefully-terminated with a standby timeout value to force a VI abort anyway, if the while loop does not exit.
I set up a simple server VI with one main while loop that does RS-232 I/O with a "running" beep on a 1 second timer. After the while loop is another small block of code that closes the serial port, and a different "terminating" beeper. When I run the VI interactively, both beeps work fine. When I use the wizard to turn it into a server and it is deployed to the SVE, the beeps begin normally. When I stop the SVE process via "remove process" in Variable Manager, the "running" beeps continue for another 10 seconds until the abort timeout occurs, even though with the wizard I specified the only while loop in the VI to be aborted.
The heat exchanger example works fine. Unfortunately it does not have any code following the while loop, so it doesn't shed any light on this issue. Ideally that example would be updated a little to show how to use the "while loop termination" feature.
Basically my request comes down to this: is there a way to actually make this work, or is it another in the list of bugs in 8.5.1?
Thanks,
Mike

While loop and for loop condition terminal

Hello friends,
I am using labview 8.6. The condition terminal of the while loop and conditional for loop is behaving in just the opposite way.
When i wire a true to the condition terminal of my loop, the while loop continues to run when I click on run. when I wire a FALSE, it stops.
Is there any setting change that I have to make it to get it work properly.
Please suggest on this.
Thanks and regards,
Herok

Please do NOT attach .bmp images with the extension changed to .jpg to circumvent the forum filters!
Herok wrote:
I am sending you the VI. I am not sure if this would help you because only in 2 computers this behaviour is seen. In others, it works as it is supposed to work.
Whatever you are seeing must be due to some corruption or folding error. It all works fine here.
To make sure there are no hidden objects, simply press the cleanup button which would reveal any extra stuff (which is obviously not there). Does it fix itself if you click the termination terminal an even number of times? What if you remove the bad loop and create a new one?
Could it be you have some problems with the graphics card and the icon of the conditional terminal does not update correctly?
Whay happens if you connect a control instead of a diagram constant?
What is different on the computers where it acts incorrectly (different CPU (brand, model), #of cores, etc.)
LabVIEW Champion . Do more with less code and in less time .

While Loop - Iteration Terminal

Why the iteration terminal in my upper while loop counts only to 1? (err_while.vi)
Petr Bilovsky
Attachments:
err_while.rar ‏289 KB

Hi PetrB
I tested your vi. Results are unexpected.
Upper loop runs to 10 and stops.Down loop keeps running and it should not, because the inputs to AND gate are TRUE.
I deleted down loop and copied upper loop ant Now they stop at 10.
I don´t know your DLL, so try to make it reentrant to avoid side efects.
Hope this helps.
Alipio
"Qod natura non dat, Salmantica non praestat"

Problem with DAQ in while loop and Graphs

Hello,
I'm new here so I apologize if I posted this on the wrong board
This is my "situation":
I need to make a simple PID controller which takes information (process variable) from an outside source (a NI's DAC connected through the USB port ) which is accomplished using NI-DAQ as an input, and the PID's output goes to the second NI-DAQ which is also connected using DAC to an actuator which in my case regulates the air pressure. (VI attached)
My problem is the following.
Both of the NI-DAQ I placed using DAQ Assist, require to be in a while loop.
-If I place them in separate loops, I have the problem of passing information between the Input NI-DAQ and the PID, and also between the PID and the Output NI-DAQ.
-If I place them both in one big loop, an error occurs saying that the selected buffer size is too small (Error -200609).
The timing settings for the DAQ's N samples, 100 samples to read at the rate of 1k (I also tried with Continuous samples and many different combinations of Samples to Read an Rate but without success).
Should I wire them with the same dt(s)?
The other thing I need to do (I'm also writing it here in order not to open new topics) is show the following 3 signals on a Graph (process variable (dynamic data type)(range 4mA - 20mA), PID output (double)(range 4mA - 20mA), and the Set Point (double)(range 0 to inf))
Firstly, is it possible to show the first two on a scale from 0 to 100 without changing the PID's output which needs to be 4-20?
Secondly, which graph should I use if I have different data types? (I tried the Waveform Chart, and succeeded in showing the first two; the third just messes everything up)
I would also have to make a legend explaining which signal is which (I see that this is possible with the Mixed Signal Graph).
I know this is probably too much to ask, but I'd be grateful for any help
Thank you in advance
Attachments:
PID while.vi ‏100 KB

My problem is the following. Both of the NI-DAQ I placed using DAQ Assist, require to be in a while loop.
-If
I place them in separate loops, I have the problem of passing
information between the Input NI-DAQ and the PID, and also between the
PID and the Output NI-DAQ.
This is the best option---Use QUEUE or Functional global or something else to tranfer the data to and fro
How do I make that QUEUE or Functional global?
-If I place them both in one big loop, an error occurs saying that the selected buffer size is too small (Error -200609).
Have
you tried increasing the buffer? Is the acquisition happening
parallelly (means to say the first DAQ not wired (error terminal) to
second DAQ)
Well the buffer is, at least how I understood it, the option Number of Samples when in Continuous Samples mode. Concerning the parallel acquisition, do you mean I should wire the error ports of both of the DAQs?

How to run a do-while loop on the 2nd execution after a stop on failure occurs?

I am trying to use the Stop on Failure process model callback from the TestStand Examples.
If a step fails within a Do-While loop and the test is terminated, the second time the test is run (continuing to the Next UUT in the process model), the condition for the do-while loop is checked first before it ever enters the loop. This is incorrect because the Do-While loop should execute once and then check the "while" condition.
Also, If I was to stop the execution altogether and then restart the test (instead of continuing with the Next UUT), it runs the loop once, then checks the "while" condition.
I'm not sure if I am describing this clearly enough. The execution seems to flow like this:
Start test
Do
NumericTest step FAILS -> terminate
Next UUT starts
While (condition is false and skips over Numeric Test step).
So it seems that TestStand thinks it's still within that Do-While loop on the second execution and whatever runtime variables are not reset correctly.
Is this a TestStand bug? It happens in both TestStand 3.1 and 3.5.
Is there any way around this?
Thanks for any help.

If it is what I think it is, it is a bug. Try unchecking Sequence Properties>>Optimize Non-Reentrant Calls to This Sequence and please tell me if that fixes it.

How do we save three 1D arrays in while loop as an excel file? I used build array, waveform. I could not make it work.

I have three separate 1 dimensional arrays in a while loop. I need to combine these arrays and save as a excel file outside the loop.
My second question is that is there any emergency STOP button in Labview so that when I press that button, it cuts all the power going to the system. Thanks...

Just a comment on the Stop button.
It's not really a good idea to rely solely on a software emergency shutdown. Especially if the shutdown is to prevent some type of hazardous condition to the people running the test. The problem is that if your application or PC in general is having some type of problem, it may not be able to shut everything down as needed.
You should always have a mechanical �Big Red Stop Button� that you can hit to cut power to everything. In addition to the button, I usually do have LabVIEW monitor things and if conditions are not looking good, have it automatically shut things down. This has always worked good, and I can�t remember any time I�ve actually had to use the big button, but it�s nice to know it�s there.
VERY IMPORT
ANT:
Using the �Abort� button on the LabVIEW toolbar is NOT the thing to do. This stops your application where ever it is in its execution and does not allow it to finish or execute any shutdown code you might have put in. A �Kill� button on the front panel works well. I�ve put a single Boolean terminal in its own little While loop to monitor it. It usually writes to a digital line that�s holding a relay on that will cut the power.
Ed
Ed Dickens - Certified LabVIEW Architect - DISTek Integration, Inc. - NI Certified Alliance Partner
Using the Abort button to stop your VI is like using a tree to stop your car. It works, but there may be consequences.

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 do I run two while loops independent of each other?

I have a simple VI. I have loop 1 with and LED and a stop button and I have loop 2 with an LED and stop button. They are both in while loops. When I run the VI,if I stop loop 1, I can not turn it back on. If I stop loop 2, it will not stop. I've attached a file with my VI.
Attachments:
2 Loops.vi ‏9 KB

bebesbabe,
This looks like a learning exercise, so I will not present a complete solution.
1. It is not polite to post to the Forum a VI which will not stop except by pressing the Abort button. The Abort button should only be used to stop a VI if something is wrong with the program during development. Add a stop button to the outer loop.
2. A loop with no delay will try to run as fast as possible, consuming all the CPU resources it can get. Since these loops are for user interfaces, delays of 100 to 200 ms are appropriate. Use the Wait (ms) function.
3. Your main problem is understanding dataflow. In LabVIEW any node may execute only when all of its inputs have been given data and it will not complete its execution until all nodes inside it have completed. Your VI does not have external inputs so waiting for data is not a factor. Each loop is considered a node. So the outer loop will iterate only after BOTH of the inner loops have stopped. On the next iteration both inner loops will be started again. Of course if the stop buttons are still pressed, the will stop after one iteration, which will seem almost instantaneous. But because of dataflow as I have described, your program cannot really work the way you want. You cannot restart one loop until both have stopped. Put an indicator on the "i" terminal of the outer loop.
4. You may wish to consider changing the mechanical action on your stop buttons to Latch when Released. Read the help to learn about mechanical actions.
The way the instructions on the front panel read, it is not clear what the intended solution is. What control or user action or program action is required to turn the loops back on? Changing the stop button? Automatically after a delay? A separate On switch? How is the entire program supposed to stop?
Lynn

How to get the loop sequence time (i) out of the while loop in the sub-vi to the main vi?

I tried to search for the answer but no much luck. My situation is that I used a sub-vi containing a while loop in my main vi. Now I need to see the while loop sequence number (i) from that sub-vi in my main vi. In the sub-vi I have the indicator to show this loop sequence flawlessly, but that's inside the loop itself. If I use this indicator as a terminal in the sub-vi, I can only see the last sequence number in the main vi after the loop finished its execution.
Is there a way to accomplish this? Thanks.

Hi nobody,
well easiest (but error prone) way is to use globals to move data from subvi to main vi. You can also give the reference of the main vi indicator to the subvi to write to a "value" property node. You can also use queues, and there are other techniques too
Best regards,
GerdW
CLAD, using 2009SP1 + LV2011SP1 + LV2014SP1 on WinXP+Win7+cRIO
Kudos are welcome

Skipping a step in while loop when boolean is switched

Hey guys,
I have a program that controls a ventilator which pumps in gas at a certain rate. This whole process is executed in a while loop. When we switch gases by a toggle that's on the front panel, we'd like to skip one ventilating cycle immediately and then goes back to pumping gases at the previous rate, but we don't know how to realize this. Can you guys give any advices? Thank you!
Sincerely,
Le Z.
Solved!
Go to Solution.

Make sure the mechanical action for the HP button is set to Latch When Released. The button will automatcially reset when the terminal is read that way.
There are only two ways to tell somebody thanks: Kudos and Marked Solutions
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Is there a way to cycle a while loop on its own and only controlled by the number of cycles?

Hello everyone,
Newcomer here, recenlty just took core 1 and 2 the past couple of months
is there a way to cycle my while loop so that the daq assist receives the same outputs from the list box table? So pretty much I need the VI to be able to read the voltages and time values from the list box and then execute them, I've manage to do this, but then I need it to stop for a given time and then execute again the same voltages. This would be controlled by a control for "number of cycles" input.
Can someone tell me why my "Emergency Stop" button doesn't stop the VI?
Why is my data logging only outputing one result if I have it to read ever min?
My wave form graph isnt plotting the temperature results, does it have somthing to do with the while loop?
I know this is a lot of questions, I'm just trying to solve this and learn from it.
Attachments:
TEST RIG 11 10-28-13.vi ‏298 KB

You took core 1 and 2!!! Please tell me NI didn't teach it. I'm not trying to harp on you too bad because I think the instructor is more to blame. You have many wires going the wrong direction, multple loops doing nothing, and one loop that will never stop so even if all the others did there would be no way to stop your program, a Stop button that is read only once at the start of the application and then is never read again (so stop will never work). You have the inner loop running forever, but even if it did stop it would run the outer loop forever, your enums should be typedefed, uninitialized shift registers when not needed, dynamic data types, far too many express VIs...ouch.
To answer your question. If you have a while loop that needs to run 5 times, why not use a for loop? Then wire a 5 to the N terminal. If you do have to use a while loop for what ever reason, use the i terminal as a condition to stop. It will start at 0 and count up so a value of 4 means it will be executing the 5 time. If the value equals 5 then stop. Get the Array size of the Listbox and set your for loop to run for each item.
Unofficial Forum Rules and Guidelines - Hooovahh - LabVIEW Overlord
If 10 out of 10 experts in any field say something is bad, you should probably take their opinion seriously.

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

Hi Guys,
I'm currently writing a code which test how long does it take for a formula node to perform its operation. The program uses a while loop to perform the calculation, and the program stops after calculating when tick count has reached 10 seconds. The program then displays the number of iterations it does in 10 seconds.
So initially I created 2 frames of sequence structure. In my first frame I have my initial tick count, and in my second frame I have my final tick count and the while loop. I used the subtract function and divide the output by 1000 to get the time difference. Then using the comparison function, I set if output > 10 then the program should stop, to do this I linked the output of the comparison function to the stop button inside the while loop.
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.
I would recommend looking at the online LabVIEW tutorials
LabVIEW Introduction Course - Three Hours
LabVIEW Introduction Course - Six Hours

If statement on a while loop condition

Hello,
I was just wondering whether it was possible to have an if statement on a while loop. Basically, I have a while loop that has the following terminating condition
do{
//...loop code here
while (netError > acceptableError && learningCycle < 100000 && alive);I'm looking to introduce a boolean "ignoreMaxCycles" that basically stops the loop from taking notice of the learningCycle clause of the condition.
do{
//...loop code here
while (netError > acceptableError && alive);I know it can be done repeating the two loops with an if statement governing which one is executed, but I was wondering whether there was a shorter/cleaner way of doing this?
Thanks,
Nick

nickd_101 wrote:
Hello,
I was just wondering whether it was possible to have an if statement on a while loop. Basically, I have a while loop that has the following terminating condition
do{
//...loop code here
while (netError > acceptableError && learningCycle < 100000 && alive);I'm looking to introduce a boolean "ignoreMaxCycles" that basically stops the loop from taking notice of the learningCycle clause of the condition.
do{
//...loop code here
while (netError > acceptableError && alive);I know it can be done repeating the two loops with an if statement governing which one is executed, but I was wondering whether there was a shorter/cleaner way of doing this?
Thanks,
Nick
do {
while(netError > acceptableError && (ignoreMaxCycles || learningCycle < 100000) && alive)wtf ? i took 2 minutes for that ?
Edited by: darth_code_r on Aug 29, 2008 9:21 AM

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

While loop termination...

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