Controlling a while loop

I have 2 parallel while loops. The main will run all the time. The
slave loop I need to turn on and off at will. Can someone present a
simple exampl have how to do this?
Thank You

There are a number of ways to do this. I think two of the simplest are in the attached image. If you want to make your code a little more robust, I'd use queue's instead of local variables, so as to prevent race conditions and have your code a little more deterministic. If you do go the local variable route, make sure the mechanical action of the control itself is one of the switching ones, because if the action is latching, LabVIEW might not catch it (which speaks to the non-determinism of locals).
Hope this helps.
Message Edited by Day on 09-26-2006 01:56 PM
Attachments:
Loops.jpg ‏41 KB

Similar Messages

How to create a time control for while loop?

Hello all,
I would like to control my while loop's execution time. In other words I want to stop while loop's execution after time (in ms) which is set by user. For example user sets 5 seconds to front panel control and a while loop runs and stops after 5 seconds.
I am not sure is it possible with the while loop. I succeed with the timed loop but it suits badly to my application. Is there any other loops for timed control if it is not possible with while loop? There is also a simple while loop with Random Number (0-1).vi as attachment.
Best Regards,
Jick
Solved!
Go to Solution.
Attachments:
execution time loop.vi ‏6 KB

hi,
see this, may be it will help.
Best luck
Gaurav k
Gaurav k
CLD Certified !!!!!
Do not forget to Mark solution and to give Kudo if problem is solved.
Attachments:
execution time loop.vi ‏9 KB

Control a while loop in the sub vi using a button in the main vi?

Dear all,
I want to be able to control ( turn on or off) a while loop in the sub vi from a button control in the main vi. How can I use the Control Reference to achieve it?
Thank you in advance.

Like this
look at attached vi's
Run the main vi
Attachments:
main_boolean.vi ‏12 KB
sub_boolean.vi ‏16 KB

Waveform charts slowed down control system while loop

Hi
In my application, I have control system which i acquire data, process and output the result. I placed some waveform charts in the while loop where i acquire data, process and output. This made while loop to miss data points( late). Is this because waveform charts store data as time passes?

Waveform charts store data in a history buffer of configurable size. You can change it to a smaller number.
What is the size of the history buffer?
How many charts are you updating in your loop?
What else is happening in your loop?
How are you updating them (wire, local variable, value property, etc).
How fast is your loop rate?
Are your plots simple (thin lines) or fancy (e.g. large dots and thick lines)?
Is autoscaling on or off?
Are the charts set to "synchronous display" by accident?
How many traces are on your chart?
What is your LabVIEW version?
What is your OS?
Do you have overlapping elements on the front panel?
Could you attach a simplified version of your code so we have a better idea what you're actually doing?
LabVIEW Champion . Do more with less code and in less time .

Event controll: How to stop a running while loop inside a event structure

Hello,
I have some problems with controlling a while loop inside a event structure (see attached VI).
I habe 3 buttons ("Start Measurement, Stop Measurement, Quit Program"). When a measurement is running, it should be possible to stop the measurement by clicking on "Stop Measurement", but this does not work.
Has anyone an idea?
Thanks a lot and best regards,
Michael
Message Edited by MichaGue_01 on 04-23-2010 04:37 AM
Solved!
Go to Solution.
Attachments:
Event_Controll.vi ‏27 KB

Hello,
Try not to use while loops inside a Event structure.
My approach is using two While loops (one will have only the Event structure).
I had to use to Flag buttons that make it a bit more complicated but i am sure somebody will come up with a better idea, or you might want to have a think about it yourself.
Have a look on the modified version on the attachment.
Once you are happy how it works then you can Hide the 2 flag buttons from the Front Pannel by going to Block diagram right-click the indicators and choose option "Hide Indicators/Controls"
I did it in LV 8.6 so i hope you can open it on your PC if not i can downgrade it.
If you have any problem let us know.
Regards
Dimitrios
Test Systems Computing Engineer
Cummins Turbo-Technologies
Attachments:
Event_Controll[1]_modified.vi ‏18 KB

Re: exit from a while loop in sub vi

I think the mail didn`t get through first time. Repeat posting - Sorry if
this occurs twice
Shane
Hallo,
Can the use of occurrences solve this problem?
The Main program can create an occurrence which can be passed to the
sub-VIs. Upon pressing the button to cancel the loop, the occurrence can be
set, instantly transmitted to all other VIs sharing which were passed the
same occurrence. Of course a small handling routine has to be written (say
a sequence parallel to the executing while loop waiting for the occurrence
and then setting the exit parameter to "true") but this is trivial.
I have checked this with a small program splitting an occurrence to three
seperate VIs and it works.
If you want, I can send a cop
y of it.
It may well be possible with notifiers or something else, but I have far
less experience with them.
Hope this helps
Shane
>pcu schrieb in Nachricht
><[email protected]>...
>>Main vi has several sub-vi's. Each sub vi has a while loop and Boolean
>>button. When program runs, sub-vi front panel appears, and I can
>>stop/continue the while loop. But when I stopped a while loop in a
>>sub-vi, I cannot control other while loops in other sub vi.
>>I need exit function from a while loop, not stop function of entire
>>program.
>>Thanks.
>
>
Using LV 6.1 and 8.2.1 on W2k (SP4) and WXP (SP2)

The notifier is probably better than occurence at this case - than it is not neccessry to write a parallel sequence.
The use of notifier is very simple, just follow an example in Help/Search example -> Advances -> Execution control -- Synchronization -> SubVI notification.
Good luck
Ferda

Exit from a while loop in sub vi

Main vi has several sub-vi's. Each sub vi has a while loop and Boolean button. When program runs, sub-vi front panel appears, and I can stop/continue the while loop. But when I stopped a while loop in a sub-vi, I cannot control other while loops in other sub vi.
I need exit function from a while loop, not stop function of entire program.
Thanks.

Hallo,
Can the use of occurrences solve this problem?
The Main program can create an occurrence which can be passed to the
sub-VIs. Upon pressing the button to cancel the loop, the occurrence can be
set, instantly transmitted to all other VIs sharing which were passed the
same occurrence. Of course a small handling routine has to be written (say
a sequence parallel to the executing while loop waiting for the occurrence
and then setting the exit parameter to "true") but this is trivial.
I have checked this with a small program splitting an occurrence to three
seperate VIs and it works.
If you want, I can send a copy of it.
It may well be possible with notifiers or something else, but I have far
less experience with them.
Hope this helps
Shane
pcu schrieb in Nachr
icht
<[email protected]>...
>Main vi has several sub-vi's. Each sub vi has a while loop and Boolean
>button. When program runs, sub-vi front panel appears, and I can
>stop/continue the while loop. But when I stopped a while loop in a
>sub-vi, I cannot control other while loops in other sub vi.
>I need exit function from a while loop, not stop function of entire
>program.
>Thanks.
Using LV 6.1 and 8.2.1 on W2k (SP4) and WXP (SP2)

How should I set up my VI so that I can use the linear fit coefficient data analysis program, when my values are coming from while loops within a sequence structure?

I'm attempting to create a calibration program, using the printer port, and a Vernier Serial Box by modifying a calibration program designed for the serial box.
There are six calibration points, and to collect them, I have it controlled by while loops so that the numbers are taken when a button is pushed, and this is inside a sequence structure so that I can get the six different points. I feed these numbers into two different arrays (for x and y values) and then try to use the linear coefficient analysis on these points, but the values for the slope and intercepts it returns are not correc
t.
If I cut out the array and coefficient analysis, and feed the same numbers in directly without the while loop and sequence structures, it produces the proper values... I don't know why the numbers it is producing are different, and I'd really like to know.
Thanks,
Karinne.

I would use a data manager sub-vi that would be called by each from of the sequence structure that produced a data point. The data manager sub-vi could auto append new items or could place items in a specific entry of an array. Later on when you want to calculate the linear fit, call the sub-vi to return the array of values.
Stu

Stop and start while loop on order

Hallo everyone,
I have this small IV, it means nothing but I want to know if it's possible to control each while loop. what I wish to do is to press the boolean button, then the while loop starts running and when i press it again the loop stops but when I press it again it works again, not that the program stops running at all. not only that but I need it for both loops. so i run one and stop the other then stop one and run the other and so on...
I dont know if this is possible and its not necessary to be done with loops, I just wrote loops because this is what I can do and understand, if there are any other possibilities then please feel free to share it with me.
Attachments:
Unbenannt 3.vi ‏178 KB

pcardinale wrote:
Perhaps something like this.
I don't think we need to involve such a huge amount of code and new concepts (timed loop, notifiers, subVIs, clusters, arrays, event structures, etc.), to solve such a simple problem. (This might turn off a beginner!).
Here's what I would do.
LabVIEW Champion . Do more with less code and in less time .
Attachments:
TwoCharts.png ‏14 KB
Unbenannt 3Mod.vi ‏17 KB

How to use while loops to implement a simple climate control.

Hi,
I am currently a 4’th year computer systems engineering student in South Africa doing a primitive climate control project in LabVIEW 8.0. Although my knowledge and skill level of LabVIEW is far from that of an expert, I really enjoy working with it. The project consists of a motor driving some fan blades, a resistor heater and an analog temperature sensor. The basic functionality entails that a user specifies a desired temperature and then the program will heat if the current temperature is lower than desired or cool if the current temperature is above the desired temperature.
What I want to add is an acceptable temperature difference so that the fan and heater do not switch constantly as the threshold temperature is reached. Rather leave the current temperature to linger between the maximum (current + acceptable difference) or minimum (current – acceptable difference) allowed temperature before heating or cooling it to the desired temperature once again.
I have attached 2 VI’s:
Final Assignment: I tried to achieve the sensible climate control by making use of a formula node. As soon as I substituted the if statements in the formula node with while statements, the VI did not respond. It did not give any errors, it just didn’t respond.
Final Assignment2: I tried the same but by making use of while loop structures. The while where my Input DAQ is works fine, but none of the other while loops work.
Please advise me on possible solutions for my problem/project.
Thank you in advance.
D. Weppenaar
Attachments:
Final Assignment1.vi ‏254 KB
Final Assignment21.vi ‏256 KB

1. Your VI does not respond because your formula node is trapped in an infinite loop and cannot exit if you're out of the deadband. Replace the words "while" with "if" (or similar) and you might be getting somewhere. Sorry, I don't have DAQ installed, but what determines the loop rate?
2. You have a dataflow issue. Only the inner loop on the left will run. All other loops must wait because they depend on data from the first loop. data is only available at an output tunnel of a loop once the loop finishes and a loop cannot start until all input tunnels contain data. Also the first loop can never stop, because the stop button is outside the loop and will never get read once the inner loop starts. The stop button needs to be in the innermost loop.
Most likely, all code segments should run synchronized, so delete all the inner loops. They serve no purpose. All yon need is the big outer loop as in the first code.
There are many ways to directly observe what is going on. For example you could run the VI in execution highlighting mode while watching the diagram.
Clearly, you need to become more familiar with LabVIEW basics. Maybe do a tutorial? Right now you might think that dataflow is a hindrance while in fact it is one of the most powerful advantages of dataflow programming. You simply need to be familiar with its logic.
LabVIEW Champion . Do more with less code and in less time .

How to stop a while loop when using tab control

How do you use a tab contol to stop what is happening on one tab when you switch to another tab? In the test example I attached, I have a while loop nested inside a case structure controlled by the tab control. When I tab to page two the elapsed timer starts but when I switch to another tab it does not stop. I can't come up with an easy way to stop or exit the while loop when I change tabs.
Thank you
Danny
Attachments:
tab control.vi ‏24 KB

I played with it a little more and came up with this fix. This fixes it but is not tied to the changing tabs as I was looking for. Is this just too many nested loops and a bad idea?
Danny
Attachments:
tab control fix maybe.vi ‏26 KB

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.

How do I break a for loop (inside) and a while loop (outside) at the same time by a control button

I have a while loop (outside) and a for loop (inside) and a control button within the for loop. I want to stop the program by click the botton without finishing the for loop. How can I do that?
Thank you in advance.

HI Please find attached snapshot Regards, Santosh
Message Edited by SanRac on 12-17-2009 05:12 AM
Message Edited by SanRac on 12-17-2009 05:13 AM
Attachments:
Snap1.png ‏4 KB

How to structure a control and its display in the same while loop and same display panel (instead of display panel and a seperate parameter-setting panel )

As you can see, I need to adjust the Target position to certain value (like 1068.88), the actual position is showing 1066.99. What kind of flow control structure will achive this goal?
Notice the Labview example "Vibration analysis" may shed some light on this issue. Will someone give out a simpler code to show how it works?
Attachments:
Spectrometer Control V3.0.vi ‏113 KB

lightblue,
Just to make sure we are on the same page, you would like to set the position, then monitor it. Is that correct? In that case, you might have a few options. You could have a sequence that would set the position, and then a while loop that would monitor the position, however this wouldn't allow you to update anything else. The other option would be to use parallel while loops, which would be similar to the parallel sequence structure you have below. The only issue with this would be that if you are calling the driver from both loops, you could run into errors. The Vibration Analysis.vi takes the setpoint, then calculates the actual available position, so it won't serve as a very good example, code-wise.
Hope this helps!
Andy F.
National Instruments

Why does Labview VI pause intermittently during motor control while loop?

I'm performing some biomechanical testing using Labview to control stepper motor actuators. I have a PCI-7334 controller card and a MID-7604 driver. The testing is run in load control using a while loop that sends a number of steps to the stepper motor that is proportional to the difference between the actual and desired load. The VI intermittently pauses though and sits in active for several seconds (~5 sec to 20 sec). What could cause this problem?
Thank you in advance for your assistance.

Without the subVIs it is hard to see what is going on.
Some general comments:
1. Block diagrams should be limited to the size of one screen. Yours is over 4 times as wide as my 27" screen.
2. Sequence structures should be avoided. LabVIEW is a datflow language and only rarely are sequence structures required. There is almost certainly a way to write your program without them.
3. The use of local variables should be avoided. Again, they have a place but most likely they are not needed in your program. They are prone to race conditions, make extra data copies, and force execution in the UI thread.
4. Floating point data types are not recommended as case selectors. They will be rounded and coerced to integers.
5. Learn about the Producer/Consumer Design Pattern and state machines.
One possible cause of your slowdown is having the Write to Spreadsheet File.vi inside the while loop. This VI is convenient to use but it opens, writes, and closes the file each time it is called. I have no way to tell how much data you write on each iteration but as the file grows the OS may need to re-allocate space for the file or fragment the file. These operations can be slow.
Do you really want to Abort the program in the False case? This will leave any outputs in the last state they had been set. This could have your motor(s) running, clutch engaged, ... In programs which control physical hardware an orderly shutdown procedure is usually better: set all outputs to a safe condition, close files, close DAQ tasks, and indicate the status to the user. Calling Stop allows none of this to happen.
Lynn

Controlling a while loop

Similar Messages

Maybe you are looking for