Metronomes, while-loops and flat sequences

I'm making a loop that is supposed to write a poll message to the serial port once every minute and read a message from the same port once every 256 ms. It is supposed to proceed untill a stop button is hit. It is based upon a while loop that contains two different flat sequence structures that each contains a metronome ("wait until next ms").
The intention of thisis that the program goes through the loop and every 256 ms it reads the serial port and every 60 000 ms it sends a polling message. However, the indicators I've connected to the metronomes doesn't seem so show a linear increase in the ms timer. The poll timer occasionally increases a little (in two minutes it might increase 20 ms). The read timer does not increase at all. Poll count increases very irregularly.
Does the flat sequences interfer with each other? Can this loop be changed in any manner in order to work properly?
Attachments:
poll_loop2.GIF ‏13 KB

The loop is dominated by the "minute" timer, what will happen is that it will wait the minute, write, go to the 1/4 minute timer do it's read, the back to the minute timer. This is because LabVIEW is a data-flow language. There are a number of different ways to do this, one being having two loops, one writing, one reading, but with out some synchronization between the two they might drift. Another method would be to have an event structure, with the timeout value set to 250 mS, putting the read and write into a case structure in that timeout event. Having a time check, or even a resetable counter (use a shift register on the loop) to determine whether to write or read, with an event for the operator to stop the whole thing. I do a diagram, but have a meeting in a couple of minutes :-)
Putnam
Certified LabVIEW Developer
Senior Test Engineer
Currently using LV 6.1-LabVIEW 2012, RT8.5
LabVIEW Champion

Similar Messages

Timed loop inside a flat sequence not terminating

Inside a while loop there is an event structure. Inside that there is a flat sequence. On one of the frames there is a timed loop that quits after so many iterations. The timed loop finishes but the flat sequence doesn't execute the next sequence. What am I not doing right?

First, you have too many local variables. This could be leading to race conditions.
I think you have a couple problems in the use of event structures. It is a bad idea to put any long running code inside an event case. It will prevent the Event Structure from handling any other events in the mean time. You have several timed loops running that in that one sequence frame.
But the bigger problem is the next sequence frame. You have a while loop that only ends once all the queues are empty. Can you guarantee that all the queues get emptied?
You have laid out the code very neatly, but you have used a lot of odd things in there. (Number to boolean array, to cluster, to unbundle the cluster to individual indicators.) Why not just go from Boolean array to and index array function. No need for the intermediate cluster conversion. Why not set up the indicators as an indicator array and just write to them directly.
The code is so much intertwined between when queues are created, filled, emptied, destroyed, events happen... And this is all multiplied by at least 4 times for each camera. And there are 4 major event structures going on. This is a very ambitious project for an inexperience LabVIEW user. You need to step back, get one thing working right, and design so that you can scale the architecture upward. Many of the structures you have essentially duplicated and belong in subVI's.

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

Execution time of a flat-sequence

Hello there -
Is there any way to get a measurement of how long each part of
the flat sequence takes to execute? Anything like matlab's "tic" and "toc"
commands in labview? I have been playing with it for a while now and
have yet to discover if Labview has this functionality. Anyone know of
anything like this?
I currently have a VI that controls the realtime acquisition of a CCD camera via Firewire and a USB spectrometer. The VI collects data from each of these devices (triggered by an external source at 10Hz), and dumps them into a Matlab script which does analysis on the CCD image and spectrum. The bulk of the VI sits inside a while loop, which continues to run until the user presses the stop button. Inside this main loop is a flat-sequence. The sequence goes: ACQUIRE DATA ---> PROCESSING DATA ----> MATLAB SCRIPT ----> PLOTTING GRAPHS -----> OUTPUT DATA TO FILE.
The problem here is that the VI runs at 5Hz, while we are triggering it at 10Hz. Originally, it was my thought thought that the matlab algorithm was to blame, but I used the matlab commands "tic" and "toc" to determine that the matlab algorithm runs in 15-20ms. I did this by putting a "tic" command at the top of the matlab algorithm and a "toc" command at the bottom. The problem, as I have now discovered is that the rest of the labview code takes ~180ms to execute. (This was discovered by putting the "tic" at the bottom of the program, and the "toc" at the top of the program, thereby measuring the execution time of everything except the matlab algorithm). Each time a trigger signal from the external source comes in, it starts the flat-sequence structure (which takes ~190ms), and then waits for another trigger signal, always missing every second signal. My eventual goal is to reduce the bloat, and get the algorithm down to less than 100ms, so that I can run the VI and acquire data at 10Hz rather than 5Hz. If anyone can offer some help with this, it would be much appreciated!
Eric
P.S. - I have attached a copy of the VI that I am working on, but unfortunately, it most likely will not run on your computer....the VI will not run unless it is connected to a triggered spectrometer and CCD camera....but I have attached it anyways incase anyone who can help might want to take a look.
Attachments:
RTSpider.vi ‏376 KB

can we divide the program into 2 parts and use background process for acquisition and front end process for analysis?
I mean, create 2 VIs from the present VI and then launch the acquisition program dynamically as a background process and fire events in Main VI from acquisition VI and process it. not sure how much it is going to reduce. lets give a try....
Anil Punnam
CLD
LV 2012, TestStand 4.2..........

How can I opearate indicator outside while loop?

I do small program, I have many while loops and I want to connect wire (in my application) from each loop to AND gate then to another while loop, but how can I operate these wires to agree with the change of my application inside while loops.
If not clear :
In another words, suppose I want to operate indicator ouside the while loop. How can I operate indicator outside while loop, so when my application become TRUE (inside while loop) the indicator will be ON (outside while loop) and when my application become FALSE(inside while loop) the indicator will be OFF (outside while loop).
Help me if you have any idea please..........................

Hi Rammo,
For the wire to carry the boolean condition from the while loop to an 'and' gate outside, the while loop must stop running
If you want the while loop to keep on running and still pass a boolean value to a destination outside the while loop, use any one of these: property nodes, global or local variables.
i am still not clear as to what you intend to say by this sentence
" I want the wire that comes out from the while loop will become TRUE if it in my application is TRUE inside while loop and the opposite is true. Because I want to connect the wire that comes out from while loop to AND gate than to another application"
plz tell me if the first part of this mail of mine answers your doubt or do you need more information?
regards
Dev

Start stop while loop with tab control

I want to be able to start and stop a while loop by entering and leaving a tab. I am using an event structure to do so but it doesn't seem elegant or the right way to do this. The only way I was able to get it to kind of work is by unchecking the lock front panel box in the event structure. I have attached a sample vi of what I have so far.
Solved!
Go to Solution.
Attachments:
Loop test.vi ‏16 KB

The problem is that you can't even stop the program by hitting the stop button until you leave the tab, which is not a friendly user interface.
Event structures should just handle basic user events. Any given event case should not take a long time to run. While you are in the diagnostics tab, your code is stuck in that while loop. Although fixing the lock front panel allows you to do other things, the LabVIEW is just queuing up all of those other UI events (like Stop button value change) and can't handle them until the inner while loop stops and allows the outer while loop to iterate again.
You should have a parallel while loop to handle the waveform graph. You can use notifiers or queues or an action engine FGV (see Ben's Action Engine Nugget) to pass the starting or stopping of the waveform graph update to the parallel while loop.

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

Re-start producer while loop

Hi,
I'm trying to figure out the best way to implement a producer/consumer architecture. I'm hoping there is something simple that I don't understand.
I have a state machine executing in it's while loop, doing things like saving and processing data. The data is being passed through a queue from a separate while loop. I'm currently starting that producer loop using occurrences, and I can stop it with a local variable.
What I can't figure out is how to restart that loop from within the state machine? In essence, I'd like to have a switch that says "Collect Data" and it will turn the producer while loop on and off but leave the main program running in the meantime.
Thanks for any suggestions.
mike

Basically, i find producer/consumer architectures where the consumer creates "commands" (Edit: which do more than simple notification tasks) for the producer quite absurd.
I would switch to a three loop architecture:
Producer A is responsible for UI display/control. It feeds Consumer A which is infact Producer B.
Producer B (aka Consumer A) is the DAQ consumer. It will acquire data due to the settings passed by Producer A. The DAQ data will be passed to Consumer B.
Consumer B handles the data passed by Producer B. If necessary, it can create custom user events in order to notify Producer A about certain situations in the software.
An approach with an Action Engine can be similar in regard to functionality, has its own advantages and disadantages.
hope this helps,
Norbert
Message Edited by Norbert B on 01-14-2010 12:13 PM
CEO: What exactly is stopping us from doing this?
Expert: Geometry
Marketing Manager: Just ignore it.

FUNCTION Cursor / WHILE LOOP vs LOOP / Logic help (RESOLVED)

(I HAVE RESOLVED - making it more efficient, I hope - see FUNCTION) if anyone has a different =, more efficient way to write this, please share...
I need help with a Function:
I am trying to get a handle on a rate. This table has and employee column this is usually populated with 'ALL'. On the off chance that it has an actual employee number, I want that rate; otherwise, the rate with ALL. Everything in both records will be the same except the employee field. (if there happens to be an ALL rate and an individual employee rate. Usually there will only be one record).
As I started to write this, I tested the WHILE loop logic and did not get a value back, but when I test a simple loop, I do. I have not finished the entire logic only getting a handle on a record that has the employee.
I would like help:
Understanding why WHILE loop isn't working
How to go about testing if CURSOR c_job_payroll_rate_emp FOUND - get this value and EXIT otherwise IF NOT FOUND then get value from c_job_payroll_rate_all
Start to my function is below w/ testing comments(** THIS IS THE RESOLVED FUNCTION.
FUNCTION job_pay_rate(in_comp_code IN jobpayrate.jpr_comp_code%TYPE,
                    in_job_code IN jobpayrate.jpr_job_code%TYPE,
                         in_phs_code IN jobpayrate.jpr_phs_code%TYPE,
                              in_cat_code IN jobpayrate.jpr_cat_code%TYPE,
                              in_trd_code IN jobpayrate.jpr_trd_code%TYPE,
                              in_emp_code IN jobpayrate.jpr_emp_no%TYPE)
RETURN jobpayrate.jpr_billing_rate%TYPE
IS
v_val jobpayrate.jpr_billing_rate%TYPE;
CURSOR c_job_payroll_rate_all IS
     SELECT max(jpr_billing_rate) rate
     FROM jobpayrate
WHERE jpr_comp_code = in_comp_code
     AND jpr_job_code = in_job_code
     AND jpr_trd_code = in_trd_code
     AND jpr_phs_code = in_phs_code
     AND jpr_cat_code = in_cat_code
     AND jpr_emp_no <> in_emp_code;
CURSOR c_job_payroll_rate_emp IS
     SELECT max(jpr_billing_rate) rate
     FROM jobpayrate
WHERE jpr_comp_code = in_comp_code
     AND jpr_job_code = in_job_code
     AND jpr_trd_code = in_trd_code
     AND jpr_phs_code = in_phs_code
     AND jpr_cat_code = in_cat_code
     AND jpr_emp_no = in_emp_code;
BEGIN
FOR rec_e IN c_job_payroll_rate_emp LOOP
v_val := rec_e.rate;
IF rec_e.rate IS NULL THEN
FOR rec_a IN c_job_payroll_rate_all LOOP
v_val := rec_a.rate;
END LOOP;
END IF;
END LOOP;
RETURN v_val;
END job_pay_rate;
Message was edited by:
KB

Rather than using cursors for zero or 1 row queries, use SELECT ... INTO
Untested
FUNCTION job_pay_rate(in_comp_code IN jobpayrate.jpr_comp_code%TYPE,
in_job_code IN jobpayrate.jpr_job_code%TYPE,
in_phs_code IN jobpayrate.jpr_phs_code%TYPE,
in_cat_code IN jobpayrate.jpr_cat_code%TYPE,
in_trd_code IN jobpayrate.jpr_trd_code%TYPE,
in_emp_code IN jobpayrate.jpr_emp_no%TYPE)
RETURN jobpayrate.jpr_billing_rate%TYPE
IS
v_val jobpayrate.jpr_billing_rate%TYPE;
BEGIN
SELECT max(jpr_billing_rate) rate INTO v_val
FROM jobpayrate
WHERE jpr_comp_code = in_comp_code
AND jpr_job_code = in_job_code
AND jpr_trd_code = in_trd_code
AND jpr_phs_code = in_phs_code
AND jpr_cat_code = in_cat_code
AND jpr_emp_no = in_emp_code;
RETURN v_val;
EXCEPTION
WHEN NO_DATA_FOUND THEN
    SELECT max(jpr_billing_rate) rate INTO v_val
    FROM jobpayrate
    WHERE jpr_comp_code = in_comp_code
    AND jpr_job_code = in_job_code
    AND jpr_trd_code = in_trd_code
    AND jpr_phs_code = in_phs_code
    AND jpr_cat_code = in_cat_code
    AND jpr_emp_no <> in_emp_code;
    RETURN v_val;
--OTHER EXCEPTION HANDLING
END;

How to call sub VI and close the main VI in while loop and sequence condition

Hiya,
I have a problem with the while loop and the sequential condition in placed together i.e while loop as Global and sequential condition as local (i.e inside the Global loop). For example,when calling the sub vi from the main vi (main vi as main menu and sub vi as sub menu.)My problem is I can't run my sub menu when the particular icon is pressed through the main menu and only the front panel appears. My concerned was if possible the sub menu is activated in few second then jump back to the main menu again (analyze through the diagram).So, I don't know what should I need to do. If possible, please advice me how to encountered that particular problem.
Thanks!

Go to your block diagram of your main menu, then click on the "Hightlight Execution" it is something like a bulb. then you execute your vi. then LV will show you all your data flow.
When you feel sad, laugh

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

Why does a sequence structure execute if a while loop is to the left of it?

I have a while loop in a case structure whose boolean is wired to a sub vi. To the right of this structure I have a sequence that executes regardless of the while loops condition. I assumed that the program would not continue to the case structure until the while loop stopped. Then it would proceed to the case structure.
Thank You

jemengineering wrote:
I have a while loop in a case structure whose boolean is wired to a sub vi. To the right of this structure I have a sequence that executes regardless of the while loops condition. I assumed that the program would not continue to the case structure until the while loop stopped. Then it would proceed to the case structure.
As others have mentioned, you have to familiarize yourself with the core idea of dataflow programming. One of the great powers of LabVIEW is the fact that things can occur in paralell unless there is data dependency.
A good start would be the LabVIEW beginners online tutorial:
http://www.ni.com/swf/presentation/us/labview/aap/default.htm
The quiz #1 on slide 11 deals with the above issues. Try to answer it.
In your particular case, you need to force execution order. This can be done by creating a data dependency (preferred) or by the use of a sequence structure. You could e.g. create a 2-frame flat sequence and place the loop in the first frame and the case structure in the second frame.
The picture shows a few scenarios for comparison. Can you spot the differences? Understanding dataflow is crucial for writing any LabVIEW program.
Message Edited by altenbach on 07-31-2006 06:49 AM
LabVIEW Champion . Do more with less code and in less time .
Attachments:
ExecutionOrder.png ‏19 KB

Continuous loop for flat sequence

Hi, I currently using LabVIEW 8.2 and still learning about LabVIEW. I’m doing a project on a FMS model using USB 6501 to run the program and I’m required to run the program continuously. I was given a program from a previous student and I’m supposed to modify the current program. The purpose of the program is to gather stock from the warehouse and place it in a different slot.
I have a sample of the program and layout of the model where the lift is to move to the left and back to the right. I’m currently stuck as I can’t figure out how to run the flat sequence continuously.
Firstly, it would just run once and stop at the right even when I’m using while loop.
Secondly, when pressing the stop button it wouldn’t stop the program midway, it would continue to run until the frame ends. Is there a way to stop the frame when an error occurs?
Please advice. Thanks.
Attachments:
LIFT LOOP.vi ‏288 KB

You definetly have to switch to a reliable architecture!
I think that your application must have several security features to prevent damage of hardware or even humans. So you must not use a program which just moves the lift from startpoint to endpoint without any chance to break the movement!
That being said, i see two approaches:
a) Statemachine
b) Producer/Consumer
The backdraft of Statemachine is its polling character. So you can only react to "worst cases" only within your given timeframe. The timeframe is the polling time plus all latencies including signal delays and similar. This can easily add up to about 1s and more.
Producer/Consumer can possibly react a little faster if it is event based. The backdraft is that you need a rather good knowledge of LV in order to implement this properly.
Another thing for applications like this are latencies created by the OS. Maybe it is necessary (not only recommended) to switch to a RT system or even FPGA in order to keep proper reaction times.....
Maybe it is a good idea to talk about this application with an NI Alliance Member .
hope this helps,
Norbert
CEO: What exactly is stopping us from doing this?
Expert: Geometry
Marketing Manager: Just ignore it.

While loop and data acquisition timing worries

Hello everyone,
I apologize in advance if this is a silly question, but I could not find the answer around here.
I have made a VI to record continuously from 64 analog channels at a 5kHz sampling rate. I then stream this data to a tdms file. The data acquisition and write functions are in a while loop.
I the same loop, I have a bunch of other loops, that each run on their own wait timers to help limit the amount of memory they take up. I am now worried that this may somehow affect my data acquisition timing.
If I put a bunch of timed loops within another loop, does the outer loop run at the same pace as the slowest of the inner loops? And could that mess up my sampling rate?
I have attached my VI, in case what I just wrote makes no sense at all.
Thanks for any tips...
Attachments:
Record_M8viaDAQv3.vi ‏237 KB

Well, looking at your code you will only write to your TDMS file one time. You have multiple infinite loops within the main/outer loop. That means that the main loop will only run a single iteration because it cannot complete an iteration until all code within it completes. With at least two infinite loops inside the loop it will never complete. Not too mention the only way to stop your code is to hit the stop/abort button. NOt a very good way to stop your code. As someone once said using the abort to stop your code is like using a tree to stop your car. It will work but not advised.
As Ben mentioned try to understand data flow better. You have unnecessary sequence frames in your code where normal data flow will control the execution sequence.
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

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

Metronomes​, while-loop​s and flat sequences

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Metronomes, while-loops and flat sequences