Time delay separate to while loop

How would I be able to obtain data (pressure read in by DAQmx) that happened 2 seconds previous?
I need to obtain the pressure difference from 2 seconds ago hence need the previous pressure with a 2 second time delay. When I try and do this the whole program delays by 2 seconds, even when I try separate the time delay through use of another time loop.
Any suggestions?

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Use the LabView time delay in a while loop instead of using the instrument inherent time loop.

I have a zes lmg500 that I use. It has the option of continues measuring data, with a user control cycle loop (still using a while loop but the delay is coming from the instrument). The problem is that the loop time is not constant. Can I use a very short time (100ms) as the instrument cycle time but use a longer time delay in the while loop that collect the data?
I know many instrument offer the same abilities, so the question is relevant to all of them.
Thanks for any help
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Does that measurement VI have built-in wait functionality and a timeout?
If not, then you are simply polling the VI at 1 kHz, but I suspect that this is not the case or your Waveform Chart probably wouldn't look as you expect (getting 0's put in everytime measurement data is not available).
I expect that if you have the instrument set up to send data at a fixed time interval (i.e. 100 ms), all the data that it is sending you will end up residing in your serial buffer (or the instrument driver will have taken it out and put it in another internal buffer), so if you come back to read it 1 sec later, then you will have 10 data points to go through. Whether you can read them all at once with the read VI or have to call it a whole bunch of times until empty I can't say.
What is your objective?

Time not stopping with while loop

Hello,
I've attached my VI. I am having trouble with while loops.
I want to turn on LEDs. The first LED should turn on after 3s. The second LED should turn on after 5s. The third LED will turn on later.
The LEDs turn on based on the following conditions:
Case 0: numeric control > 10 then led_1 off, led_2 off, led_3 off
Case 1: numeric control <= 10 then led_1 on, led_2 on, led_3 on
Case 2: numeric control <=5 then led_3 on
Because of the way I'm delaying time, I have the following problems
Case 1 --> case 2: led_3 doesn't come on right away
Case 2 --> case 1: led_3 doesn't turn off right away
Putting probes in certain areas leads me to believe that these problems are due to the way the time delay is being generated.
Thanks in advance.
EDIT: Looking at it more...it seems to be that when the stop condition is true, the loop runs one more iteration. Is there a way to keep it from running that "one more iteration."
Attachments:
timing.vi ‏15 KB

One of the problems is that your VI is not able to "breathe" because it is sometimes trapped inside inner loops that consume all CPU and step on each others toes. All you need is an single outer loop and a few shift registers.
May of your specifications are still not clear, for example what should happen to LED 1&2 in case #3? Should they remain in the state they are in, or should they turn off, for example.
Here is a simple rewrite that spins the outer loop at a regular rate, has no inner loop, and does not need any local variables or value property nodes. See if it makes sense. Also note that your code can be simplified dramatically by using arrays. Since the stop button is read with each of the regular interations, we don't need to worry about sequencing.
Most likely you need to do a few simple modofications, because your specs are not clear.
LabVIEW Champion . Do more with less code and in less time .
Attachments:
timingMODCA.vi ‏15 KB

Capturing of time taken by a while loop in bpm

Hi ,
I have a busniess process ,and my receive step is defined in a while loop.
so it starts with a while loop.
I want to keep a condition on the while loop that it should receive the messages only for a period of 1 hour ,and if it exceeds this period it should end up the process triggeringa mail.
I mean to say if there are 12 records to be processed through the while loop ...and if I receive only 11 records ..it will be waiting for that final record in an infinite loop ..so I dont want that ...instead if the total no of records are reached then it should move forward ..If it is waiting for the missing records for an hour ..I should stop the process and trigger a mail to the queue monitor saying that record is missing...I have finished the process without this processing time condition successfully..
I am new to XI and I dont have any idea on how to capture this processing time of while loop.
can some one please help me out in this issue...
Thank you in advance...

Hi Latika,
Yeah I understand we can go with fork but why I am going with this is ,I have already designed a Payload dependent loop ,by using while loop.so it makes my job simple ...
Now I am converting it to time dependent loop,so only the final question I have is...In the time dependent loop documentation ..they have taken it as infinite loop and only kept the time limit in the deadline branch...so when the deadline reaches they trigger something.
If you go to the documentation of time dependent loop(http://help.sap.com/saphelp_erp2005vp/helpdata/en/08/16163ff8519a06e10000000a114084/content.htm) ..they took the infinite loop...in this loop if I mention the counter ..and if this record count triggers before the time limit...it should come out of the block...would it work this way ?
Thanks a lot...

Time Measurement in a While-Loop

Greetings gentleman;
I am a little bit new at Labview, and though i searched for an answer without posting, i was not able to find one.
So here is my question, i would like to know how can i measure time of a loop sequence, in other words, how much time does my VI take to execute the whole main loop ?.
A little explanation, the attached VI tries to be a Markov Chain, it takes some values in the first case structure depending of the previus loop, then, if the values are correct, it goes to the next step and so on. It is quite simple, yet, my issue lies with the time measurement. Since this is a probability "distribution" it could take infinite time to execute one single loop if it does not meet the requierements, but is programmed to meet them so an average timing should work.
So, if you look at the While loop, the big one, that i would like to measure how much time does it take to do one round.
Thanks for the help, i would be glad to read some ideas on how to measure that.
Kind regards,
Stgo.
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Attachments:
Markov Chain.vi ‏30 KB

You can find a few examples in the NI Example Finder by searching for 'speed test' or 'benchmark'.
Essentially, you create a flat sequence structure inside your while loop. In the first frame, you measure the current tick count. In the middle frame, you run your code. In the final frame, you measure the tick count again, and subtract the first count from this. This gives you the execution time to run the code.
You can see a community page on it here.
There's a high resolution tick/time count VI hanging around somewhere which is excellent for benchmarking and improving efficiency, used in place of the Tick Count (ms) primitive.
Edit - remembered where it was
https://decibel.ni.com/content/blogs/EvanP/2010/10/04/tick-count-us--microsecond-timing-granularity-...
CLD

Why the execution time increases with a while loop, but not with "Run continuously" ?

Hi all,
I have a serious time problem that I don't know how to solve because I don't know exactly where it comes from.
I command two RF switches via a DAQ card (NI USB-6008). Only one position at the same time can be selected on each switch. Basically, the VI created for this functionnality (by a co-worker) resets all the DAQ outputs, and then activates the desired ones. It has three inputs, two simp0le string controls, and an array of cluster, which contains the list of all the outputs and some informations to know what is connected (specific to my application).
I use this VI in a complex application, and I get some problems with the execution time, which increased each time I callled the VI, so I made a test VI (TimeTesting.vi) to figure out where the problem came from. In this special VI I record the execution time in a csv file to analyse then with excel.
After several tests, I found that if I run this test VI with the while loop, the execution time increases at each cycle, but if I remove the while loop and use the "Run continuously" funtionnality, the execution time remains the same. In my top level application I have while loops and events, and so the execution time increases too.
Could someone explain me why the execution time increases, and how can I avoid that? I attached my test VI and the necessary subVIs, as well as a picture of a graph which shows the execution time with a while loop and with the "run continuously".
Thanks a lot for your help!
Solved!
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Attachments:
TimeTesting.zip ‏70 KB
Graph.PNG ‏20 KB

jul7290 wrote:
Thank you very much for your help! I added the "Clear task" vi and now it works properly.
If you are still using the RUn Continuously you should stop. That is meant strictly for debugging. In fact, I can't even tell you the last time I ever used it. If you want your code to repeat you should use loops and control the behavior of the code.
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

Real time waveform graph in while loop

Hi
I have a VI which includes a subVI that reads data from an oscilloscope and presents the output in the form of a cluster made up of the initial time t(0), a time interval delta t and an array of voltage readings.
This cluster can then be wired to a waveform graph in the usual way. All of this is situated within a while loop in my VI and on each iteration of the loop I obtain a waveform graph of the voltage readings starting at the same time t(0) and ending at the same time t. However I want my graph to begin at a time t(0) when I set my VI running and then continuously acquire and build up the data on each iteration of the while loop so after my VI has finished executing I have a complete graph of all the voltage readings acquired after the set number of iterations of the loop. I know on the Express X-Y Graph VI you can double-click the node and deselect the box that says 'clear data on each call' - if I could do this in my case that would be great but I can't use an x-y graph because I have an array of y-values to plot on each iteration.
If anyone can help me out it would be much appreciated - I'm sure there must be an easy solution to this but I'm going out of my mind trying to find out what it is!
Many thanks,
Bex.

As usual, you have several options.
You can use an XY Graph by generating the X values yourself. This will ensure that you place the data exactly where you want it on the X axis. This is fast, but does involve a memory cost.
You can use a Waveform Graph with a waveform input instead of the cluster you are using. Use the Build Waveform primitive instead of the bundler to make your waveform. Set the t0 values to the appropriate values (negatives do work, as do small numbers - time is in seconds, use the To Time Stamp primitive to convert from DBL to timestamp). Finally, you need to set the Waveform Graph to use the t0 values. Pop up on the Waveform Graph and make sure Ignore Time Stamp is not checked. Depending on your version of LabVIEW, you may have to pop up on the graph or the axis. When you unselect Ignore Time Stamp, you will probably want to reformat the X-axis again. The Waveform Graph clears data at each iteration, so you will need to replot all your data each time. Just create an array of waveforms and keep adding to it. The t0s will put the waveforms in the right places. Yes, this may cause memory problems.
Finally, you can use the Waveform Chart, which does have memory. Create the waveforms like you did for the Waveform Graph and send them to the chart. It will remember what was sent to it from run to run. Make sure you set the Chart History Length (pop up on chart and select Chart History Length...) to long enough to hold your entire data. You can use a property node to get the data back at the end, if you need to.
Good luck!
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How to stop execution in while loop without stopping execution of other loops in the same vi

HI
I am quite a novice in Labview.
I have a problem in my project. I used a while loop inside my vi to build an array of ten values along with other loops. Then I used a stop button to stop manually the while loop. But it seems like the loop doesn't stop in the middle of the array building and so other loops in the vi doesn't work until the while loop finishes building the array and as soon as while loop execution is over, the complete vi stops. But all that I wanted was to build the array using the shift register along with the control to stop building array anytime. And not to stop execution of other structures when the while loop finishes.
Can anyone help me?
Rahul

Hi Rahul,
Modified ur Vi to work with single button.
But the subtract case is not in any loop.
So, once both the loops stop, the subtract case will execute only once. Depending on state of subtaract boolean at that time, corresponding case will be executed and the Vi will stop.
so think of a logic where u can put this also in a new loop.
Or you can also incorporate it in one of the two loops and pass the other loop's data to it.
Let us know how you will proceed in this regard
I am posting your VI as well a VI with my modifications VI in Labview 7.0 so that Thomas can give his suggestions too
Plus, always keep a time delay in your while loops.
Oh sorry, the "arrayinouttestnewfinal.vi" is the modified vi
Regards
Dev
Message Edited by devchander on 01-10-2006 06:15 AM
Message Edited by devchander on 01-10-2006 06:19 AM
Attachments:
arrayinouttestnewfinalnew4.vi ‏59 KB
arrayinouttestnewfinal.vi ‏63 KB

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

DAQ AO to AI time delay

Hallo,
I'm working on an academic control project, where I need to read (ni9215) 3 or 4 channels very fast,
process the data and write them back (ni 9263) via usb-chassis 9172. To check the accuracy and time
delays I tried a loop from AO to AI (only one channel) and generated a step, saved the timestamp of the
step and checked, when the step was readed in the written measurement log. I doesn't see andy difference
in using two VI's to read and to write or combining them in one VI, so I added images of two VI's.
While comparing the timestamps of the sampled step and the log file, i noticed time delays of about 200ms
from output to input. So my VI's are times too slow for my control purpose... anybody knows, what to try?
In this VI I read data with 500hz, 10 samples to read and 10 samples/channel. The read timeout is set to
default, but if I set it to zero, strange (negative) times are written to the measurement log... I tried
to change from N samples acquisition to single sample acq, but it didn't speed up the VI.
Thanks for answering!

Hi IoInNBlack,
first of all thank you for posting in this forum.
I think you should synchronize your input/output operation, otherwise I don´t understand how you can take the timestamps and consider them
reliable for your evaluation. I suggest you to modify the LV example here attached with timestamps and file I/O to build up your test and see what results you get then. Consider also that 20 ms are necessary for the acquisition of the samples and then you have add the time necessary to manage the file I/O.
Best regards.
Andrea P.
Message Edited by pxchellone on 07-06-2009 09:23 AM
Attachments:
Multi-Function-Synch AI-AO.vi ‏35 KB

Other choise to while loop polling?

Hi!
I have worked with USB-bus oscilloscope and trying to build labview software using dll-librarys. Almost everything works BUT... how i can poll dll-library (*.vi) which is external "counter"? I know that dll is returning number of samples from scope hardware and i know number of those samples are 3072 blocks. Now when I polling that dll in while loop it returns just something (2999 or 3001 or 2989 or something like that). I think that dll returns that value which is exactly time in dll when while loop poll it? Hardwares speed is 50Msps 8-bit. How else i can poll that dll? Or other choises to while loop, where i have to poll something and when it returns something then do something...
Thx again

Here are two choices (could be more out there): Active Polling or Event Registration
Active polling = use of while loop with your DLL calls. This makes sense if you know there is always data available to retrieve. Caveats include processor usage, which can affect UI response and processing.
Event Registration = use of Event Structure with Callback (e.g. Active X callback), such that your hardware notifies the OS when data is ready. This makes sense if you are not always capturing data in your top level code and if your hardware driver includes callbacks. Caveats include more complex programming (understanding of Active X, dynamic event registration, event structure, etc.)
If you're having trouble understanding how you might integrate these into your main application, in addition to these forums, there are also NI Certified Alliance Partners (like us) that can help you get going.
Message Edited by LabBEAN on 08-17-2009 12:33 PM
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Separate Views from Implementation for Strict Type Defs

Multiple DAQ Cards, Multiple While Loops

I'm writing a code to support 3 small test stands that each have the same outputs and inputs as the others. I'm running them all off of an 8-slot DAQ. Each test stand has its own dedicated RTD Card and Analog Out card, but they all share a 32-channel Analog Input card.
I'd like to decouple the 3 test stands as much as possible - if I have to take out an RTD card or Analog Output card, I don't want the entire LabVIEW program to stop running. I want to be able to keep running and logging data on the other two test stands if I were working on the other test stand. Is there a way to do this with only 1 cDAQ? Is it simply a matter of creating separate, independent while loops for each test stand? If so, would LabVIEW have issues with each while loop writing its own measurement file in parallel with the others?
Thank You.

Is it safe to assume you've been running the three tests? Some of your post makes it sound like you've run them coupled while other parts make it sound like you haven't successfully had all three tests running simultaneously.
If you aren't running them, are you using hardware timing (counters) for your tasks? If you're looking to use counters, you're only using one per task, correct? The cDAQ will only have four counters total to be shared between your loops.
I can't remember off the top of my head if it is the task or the computer that reserves a cDAQ chassis. I want to say it's the computer so you can run multiple tasks from the same cDAQ. But, you'd still need to choose ctr0, ctr1, ctr2, etc in each task so that you don't share these resources between tasks.
Are you looking to pull the shared module out frequently? If not, are you gaining enough functionality to justify buying two redundant modules to gain decoupling?

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

Contradiction between time delay and fetch bmp file

Hi All,
I need to fetch BMP file by confirm.vi(pic2), but when I run the program, the BMP file won't come out correctly. the last picture always come out. (for example, the first time picture A come out, but when picture B should come out, it still show Picture A.)
the correct picture will come out correctly when i put time delay 100ms in the loop. but it will cost lost of time,two arraies have 300 elements and 20 elements separately. how can I make it faster to fetch the correct picture? thanks!
Solved!
Go to Solution.

So you are using a file in order to pass data between loops? That a major race condition. Try using a User Event, Queue, or Notifier to send the picture to your other loop.
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How can I put a time delay between specific events in a while loop?

How can I put a time delay between specific events within the same while loop? I'm already using the "wait" command to control the overall loop iteration speed. But I want to time the individual events as well.

Hi Jesse,
You can use a flat sequence. In each box you can put your individual events and attached wait.
Don't forget to reduce your total loop time of the time you added in the individual sequences.
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Time delay separate to while loop

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