Event Structure need to reset?

Refer mini vi I made attached. I click on the x button at top right, a message box pops up for confirmation. But if I click second time on x, no more message box pops up.
Now do i need to reset some properties or do some extra wiring at the vi? I have been refering to the examples but cant figure it out.
Thanks.
Solved!
Go to Solution.
Attachments:
test.vi ‏8 KB

Hi,
You must put the event structure into the while loop. Otherwise, it runs just once.

Similar Messages

Event structure inside a case structure

Hi,
I've got a problem w/ my porgram, and managed to boil it down to this
simple example. The program basically hangs if you change the
Numeric value when the boolean is false. I don't understand
why. I suspect it has to do with the way event structures are
treated, but if someone cou please explain this I'd be greatful.
Also, now imagine I have 7 numeric controls, handled by 7 cases in that
event structure, and I actually want to do things in response to the
value change for each. Can someone suggest an elegant way to do
that? I thought what I had here was a good design, but apparently
not.
Bjorn
(I'm using labview 7.1)
Attachments:
EventInCase.vi ‏24 KB

It is generally a bad idea to place event structures into cases. Events structures need to be able to breathe.
Maybe you can redesign your program and place the case structure inside the event structure, for example? (Also have a look at the online help for the event structure, especially the link "caveats and recommendations for using events ".)
Detailed analysis:
Your event case for the numeric is set to "lock front panel until event completes". If you change the numeric while the case is false, the evet structure cannot execute, so the front panel locks forever. The observed behavior is as expected. All clear?
In addition, if the case is false, the main loop spins at nearly infinite rate, consuming all available CPU. Place a small wait to be more cosiderate to everything else running on your rig.
LabVIEW Champion . Do more with less code and in less time .

Using an event structure to reset a boolean control with ring menu value change

I am trying to get two boolean buttons to reset when the value of a ring menu changes. For this I am using an event structure set to execute with a ring value change. However I have other code that needs to be executing while the event structure waits for the value change. I place my event structure inside the while loop the buttons reset as expected but my other code does not run (except at the moment of value change). If I place it outside the loop the rest of the code functions as expected but the buttons do not reset. Any help you can offer is much appreciated.
Solved!
Go to Solution.
Attachments:
event structure reset.vi ‏11 KB

try this
Attachments:
event structure reset_edit.vi ‏14 KB

Resetting a variable in an event structure (dynamic event)

I'm working on moving an event structure into a sub VI. This means I have to register dynamic events.
The event structure is handling some button clicks. The state of the button (mechanical action = latch when released) resets itself automatically as long as the variable is placed within the value change case. Leaving the button in this case is not possible when the event structure is put in a sub VI and the variable is located in the parent VI. How do I make sure the button unlatches after clicking on it? I have attached an example where all the code is in one VI (the local variable must be moved outside the event structure in order for it to be moved into a sub VI). Any ideas?
If you open the VI and run it, you can click Start which will cause the counter to start incrementing. The button only unlatches as long as the variable is located in the value change case.
(Btw, how do you put images inline in a post?)
Rob
LV2011,LV2012,LV2013
Attachments:
img.png ‏18 KB
main.vi ‏17 KB

Race conditions are the primary reason not to do that. But since your treating your variable as a latch, I doubt your using the value you read from it anywhere, and in that case it can't create a race condition. There's also the possibility that the control's reference could become invalid. But since this is a sub VI of the control's VI that can't happen (even if it could you can check the error out of the value property node to see when it happens and deal with it).
I'm not sure about the flickering, Since I can't seem to duplicate it with a simple test case on my machine. It might related to whatever else you're doing in the event apart from reseting the value to false.

I need help with event structure. I am trying to feed the index of the array, the index can vary from 0 to 7. Based on the logic ouput of a comparison, the index buffer should increment ?

I need help with event structure.
I am trying to feed the index of the array, the index number can vary from 0 to 7.
Based on the logic ouput of a comparison, the index buffer should increment
or decrement every time the output of comparsion changes(event change). I guess I need to use event structure?
(My event code doesn't execute when there is an event at its input /comparator changes its boolean state.
Anyone coded on similar lines? Any ideas appreciated.
Thanks in advance!

You don't need an Event Structure, a simple State Machine would be more appropriate.
There are many examples of State Machines within this forum.
RayR

Need to paste on/off button in its own event structure?

I am studying the CLD exam car wash vi attached.
First question, I noticed the Start button is pasted inside its own event structure. Is this absolutely necessary, can I just paste somewhere else?
I guess it was paste there because the Start button has no wiring so it looks neater to paste in its own event structure, am I right?
Second question, I noticed the Stop button is already wired to the red while loop stop, so pressing it would stop the vi already. But there is also the Stop value change event, this looks redundant, no? Or is it something really necessary??
Solved!
Go to Solution.
Attachments:
Car Wash LV86.zip ‏73 KB

Both are necessary.
1. The boolean's terminal while be read when the event is triggered. This read triggers the latch operation (so the button snaps back).
2. The event structure would wait for an event and nothing would happen until another event is triggered. Only after the event structure is 'run', the stop value is read.
Felix
www.aescusoft.de
My latest community nugget on producer/consumer design
My current blog: A journey through uml

Event Structure Freezes Vi After Capturing The First Event

My Event structure catches the first instance of my button press but then it freezes my Vi. The reason is because of the while loop but I need the while loop to constantly read from a serial port and send data to a serial port. The vi included is stripped down to be just a while loop that does nothing. I have also tryed putting the event structure in the while loop, but the same thing is happening.
Any ideas?
Thanks,
Cason Clagg
SwRI
LabView 7.1, Windows XP

Also, put the button inside the event structure where it is acted upon, from LV help (suggest you read the entire events section of help):
When you trigger an event on a Boolean control configured with a latching mechanical action, the Boolean control does not reset to its default value until the block diagram reads the terminal on the Boolean control. You must read the terminal inside the event case for the mechanical action to work correctly. As a reminder, a note appears in the Edit Events dialog box when you configure a Value Change event on a latched Boolean control.
Refer to the Handling a Latched Stop Boolean Control in an Event Structure caveat for information about how to handle a latched Boolean control.
When you trigger an event on a Boolean control configured with a latching mechanical action, the Boolean control does not reset to its default value until the block diagram reads the terminal on the Boolean control. You must read the terminal inside the event case for the mechanical action to work correctly. As a reminder, a note appears in the Edit Events dialog box when you configure a Value Change event on a latched Boolean control.
Refer to the Handling a Latched Stop Boolean Control in an Event Structure caveat for information about how to handle a latched Boolean control.
~~~~~~~~~~~~~~~~~~~~~~~~~~
"It’s the questions that drive us.”
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Producer/Consumer Design Pattern + DAQmx + Event Structure

Dear community users,
at the moment I try to implement the Producer/Consumer Design Pattern into my current project. For this purpose I am trying to make a "minimal-example" in which I use the Producer/Consumer Design Pattern for the data acquisition and analysis (display in GraphXY, calculation etc..) process. In the Producer Loop I perform the data readings via DAQmxRead.VI and in the Consumer Loop, in this example only, I display the data in a GraphXY. At the same time I want to control the data acquisition via an Event Structure, for example Start Measurement/Stop Measurement Buttons. To configure the measurement time, for example if the user only wants to measure 150 sec, I use the Time Out Event of the Event Structure. This is a technique which is often used, when data acquisition and Event Structures are used at the same time (Excuse me if this is wrong!). Due to understand the Producer/Consumer Design Pattern I looked up in the Template\Framework of LabVIEW.
In the attachment you will find my "minimal-example", which -sadly-, not working. What should I do ?
Thank you.
Best regards,
tugrul öztürk
Attachments:
daqEngine_PCP.vi ‏35 KB

Your VI will never stop due to the Ok Button that stops the producer loop is read OUTSIDE of the loop. Add an event case for it.
Move the Start and the Ok Button inside of their respective event cases. This will allow the latch to reset when they are read.
Change the Ok Button to a stop button.
Use a Greater Or Equal instead of Equal for the measurement time comparison. What if somebody randomly changes it to 0 on you? Again, you will never stop.
Is the DAQ only supposed to read for "Measurement Time". Right now, it constantly reads. So if you don't use the DAQmx Read, you will get a buffer overflow error. You need to put the DAQmx Start Task inside of the Start event case and then the Stop DAQmx Task inside of the Timeout event case when the measurement time is exceeded. You should also perform the read regardless inside of the Timeout event case.
I HATE telling the consumer loop to stop by destroying the queue. You can look data that way. Instead, send something an empty array. In the consumer, check for an empty array. If it is empty, stop. Destroy the queue only AFTER BOTH LOOPS HAVE COMPLETED.
You should also report your errors in some way. Simple Error Handler at the minimum.
Since you are using Continous Samples, don't limit the buffer. Leave the Samples per Channel unwired on the DAQmx Timing VI.
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How to implement boolean comparison and event structure?

Hello all,
I'm currently developing an undergraduate lab in which a laptop sends out a voltage via USB-6008 to a circuit board with an op-amp, the voltage is amplified, and then sent back into the laptop. The student is going to have to determine an "unknown" voltage which will run in the background (they can do this by a step test, graph V_in vs V_out and extrapolate to the x-axis).
Currently, I have two loops that are independent in my VI. The first loop is used to "Set the zero." When 0 voltage (V_in) is sent out of the laptop it returns a value around -1.40V (V_out) typically. Thus, I created the first loop to average this value. The second loop, averages the V_out values that come into the laptop as the V_in numeric control changes. Then I take the "set zero" value from the first loop and subtract it from the second loop average to get as close to 0V for V_out when V_in is 0V.
The problem I'm facing is, the event structure waits for the V_in numeric control value change, but after "SET ZERO" is pressed, if there is an unknown value, it will not be added to the average for V_out until V_in is changed by the user. So, I tried implementing a comparison algorithm in the "[0] Timeout Case." This algorithm works for step tests with positive values for V_in, but there are two problems.
1) Negative values cannot be used for V_in
2) If a user uses increasing positive values for V_in there is no trouble, but if they try to go back to 0, the value change event has been called and it is added to V_out as well as the timeout case.
Sorry for the extremely long post, but I've been banging my head over this and can't figure out how to properly implement this. I'm using LabVIEW 8.0.
Attachments:
Average Reset Test.vi ‏371 KB

OK you have bigger problems than Raven's Fan is pointing out.
When the first event loop stops ( after pressing "") (the boolean text is "Set Zero") The second loop may start- (AND PROCESSES all of the events it was registered to process before the loop started!) that would enclude the value change event from "" (The boolean text is Stop) Being pressed bebore the loop started. Of course, since the labels of "Set Zero" and Stop are identical nulls....................................................BOTH event trigger at the same time and are processed as soon as the event loop they are registerd to is available.
Get it ... The two buttons labeled "" both queue Value change events to both loops registered to act on the value change of the control labled ""!
Both loops will do what you programmed in the case of "" Value Change! This can, (as you have observered) lead to confusing code actions.
Do avoid controls with duplicate labels (There is a VI Analizer test for that!) Do avoid multiple event structures in the same hierarchy.
DO NOT bring this to your studients to help you learn LabVIEW! We get enough studii asking embarassing questions
VI Analizer will help you provide sound templates. If you need help with that hit my sig line- e-mail me and I'll always be willing to help.
Jeff

Event Structures-best way to implement this UI?

I am trying to write a VI to control & read data from 4 different "channels" (each measuring a DUT) at once. I have written all the VI's for initializing instruments, communicating with the devices (VISA, GPIB), setting bias, reading data, etc...that has all completed. I just need to write the overall program with the user interface to allow the user to control these 4 channels & display the measured data.....as it turns out, this is the tricky part! My head is spinning from trying to figure out how to handle all the possible events.
Basically for each channel, I want the user to be able to
-enable/disable it for measurement (e.g. if there is no device loaded in Ch.3, we don't want to measure Ch.3..maybe disable/grey everything)
-set bias conditions (only if channel enabled). Allow user to change bias "in real-time" by increment/decrementing (e.g. incrementing from 5.00 V to 5.01 V, for example).
-turn biasing on/off (again, only if channel is enabled)
Also, I want each channel to display its measured data (e.g current, temperature reading)..every second or so. No graphs or anything fancy (for now! ), just numeric indicator.
Honestly, this all sounds so simple but I'm having trouble figuring out the best way to implement this, due to the fact that 1) there are multiple channels needing to be monitored for events 2) large number of user events that could occur (seems like at least 4 per channel - enabling/disabling, turning bias on/off, incrementing/decrementing bias values, etc ), Also the if a channel IS enabled, i want to be continously reading/displaying the data. What is the best way to handle this? Should i have 4 separate while loops, each with an event structure to handle events for that particular channel..or will that give me grief somewhre?
Also, I have another nagging question. Pretty much all the examples I see re: Event Structures and booleans involve latched booleans, eg. buttons that are just pressed once and pop back up...e.g. buttons you press to tell it to complete a task (e.g. "Acquire Data" or "Stop") , and once it's pressed it's over and reset. In my case, some of the booleans would not be latched...e.g. the "Enable Ch.2" button would be 'TRUE" as long as i want Ch. 2 to be read....does that make sense? Then, say hours later, if i did want to disable that channel, i would change it to "FALSE" and while that would be an "value change", the new value would not be "TRUE"..does that make sense? So not sure if that would be dealt with the same way in an Event Structure.
Hope this all makes sense and many thanks in advance for any help!!!

You're halfway there. I'd say the best solution is a producer/consumer structure, the event structure is used to generate queued commands to the consumer loop.
All data is handled in the consumer loop, where you among other things have an array of clusters of channel/instrument settings. (I usually have several cluster, one for test data, one for instrument settings, one for general settings and so on)
The event structure can have a 1 sec timeout, in which you queue up a Measure command.
In the consumer, in the measure state you loop through your instruments and if enabled you measure them and update their indicators.
The general (smart) way to setup the queue is with a cluster containing 2 elements, a typedef'd Command and a variant.
This way you can send data with the command in any form which is then interpreted in the consumer.
If, e.g. you press the Enable button on a channel, you can enqueue Enable and the channel number.
/Y
LabVIEW 8.2 - 2014
"Only dead fish swim downstream" - "My life for Kudos!" - "Dumb people repeat old mistakes - smart ones create new ones."
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Event structures for dummies

After all the great help with data handling, I thought I would ask a question about event structures.
I have a main VI that sits around and lets me read in files and change variables. Once I am happy, I press start which fires up some sub VI that start running in the background. I have tried this using event structures. But then disaster strikes!! One of my variables is wrong and I need to stop/reset the sub VIs (without stopping the main program). However, my subVI is running in a timed loop continuously, within the event structure, so it's stuck. Attached is a very simplified VI of what I mean.
I basically want to run a program, set up some variables, set off a background subVI, update/reset if needs be and then press the big continue button to the next stage whilst the subVI is still chugging.
Any suggestions from the Guru's? I do not think event structures are the way forward
"When I read about the horrors of drinking, I gave up reading"
Attachments:
event structures for idiots.vi ‏90 KB

The important thing about event structures is to use them in the right way. For example as a rule of thumb, don't put into an event handler anything that will take more than about 200 msec or so to complete. Why? Studies have shown that 200 msec is the longest delay you can generate without the user noticing the delay (obviously YMMV).
One good solution (as corys pointed out) is the Producer/Consumer Loop - but there are a variety of others. For example, I have created applications where pressing a button launched a long task as a separate process running in the background. When it finished it passed data back to the GUI using another event, queue or some other mechanism.
Mike...
Certified Professional Instructor
Certified LabVIEW Architect
LabVIEW Champion
"... after all, He's not a tame lion..."
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While loop with stop button within event structure locks up front panel.

I am not sure if this is a bug with my program or a bug within LabVIEW. If you believe that this is a bug with my program then I will post my program to be looked at.
The problem I am having is there is a while loop within an event structure that fires when a particular value changes. Once the "Activate" button is pressed the while loop within the event structure starts going with a polling frequency of 1hz (1000ms wired to the "wait till next ms multiple" vi). There is a "Deactivate" button that is wired to the stop control of the while loop and an outter while loop that resets the event structure so that the activate button is being listened to again.
Once inside the while loop, however, none of the button are responsive within the front panel. The VI continues to run, and only 60% of my CPU is being consumed, but none of the button or scroll bars work. The only way for me to terminate the program is with the "Abort" button next to the "Run" button. If I remove the event structure so that the while loop in question runs as soon as the program starts, the front panel remains responsive. I've inserted probes within the while loop and verified that it is not running prior to the "Activate" button being asserted, and it is running after the assertion of the "Activate" button with the expected polling frequency set by the "wait till next ms multiple" vi.
Can anyone help? Do I need to post my code?
-Nic

It is typically not a good idea to stall an event structure by placing loops inside event cases. What good is an event structure if it is not free to repond to events?
Have a look at some alternative solutions, such as in the following link:
http://forums.ni.com/ni/board/message?board.id=170&message.id=224817#M224817
LabVIEW Champion . Do more with less code and in less time .

Acquiring continuous data using an event structure

I am new to labview, having recently taken the Core I and II courses.
I am programming a test rig to acquire the linear position of a hydraulic cylinder and plot it over time. In programming this code, I elected to use an event structure so that when a front panel button is pressed, a certain part of the test is run.
In one particular part of the test, called the Snub Test, I need to measure the position of the cylinder over time and plot it to a graph. The data acquisition needs to be continuous, however the event structure only allows the loop to run once.
I have attached a portion of my code for reference.
Can someone please advise how I can get this data acquisition to run continuously until the user (or a reference trigger) stops the test?
Thanks
Attachments:
Front Panel.vi ‏115 KB

A few comments to your VI in general:
You changed the stop button to "switch until released", most likely because you fabricated a race condition and did this as a quick fix. The reason is (1) your placement of the stop terminal outside the event structure and (2) the use of a local variable wired to the stop condition. The button terminal of a latch action boolean belong inside it's associated event case! This way it gets read (and reset to false) when the event occurs. In your case, the local variable and the button get read before the event occurs and the loop needs to spin once more at the event that occurs when you release it (true->false). At this point, the local is still true from the earlier event and the loop stops. Correct would be: latch action, stop terminal inside stop case and wired to the stop condition from inside the event. Other cases use the default output (false) and don't stop the loop.
Your "equal false" code fragment is just an invert, right? So why complicate things?
Why do you need a wait if there is an event structure?
LabVIEW Champion . Do more with less code and in less time .

Loop with event structure

I put an "event structure" inside of a while loop. My target is to keep the
VI running and make selections to run different subVI. But I got two
questions:
1. how to use two button on front panel? I mean, when I press one button,
step 1 runs, when I press the other button, step 2 runs. Is event structure
the best way to do that? another side quesition is that how I can make the
button jump back after I pressed it? It kept in the "down" position and I
have to press it again to release it.
2. When I test the VI, I found the while loop can't stop. The boolean input
of false won't stop the VI. I wonder if there is a rule that the event
structure must run at least once? or any other hidden properties I didn't
notice?
thank you very much!
cheng

"Michael Sachs" wrote in message news:...
> You can change the boolean's mechanical action to a latched type and then it
> will pop back up.
> The event structure has a timeout input that defaults to infinite. If the
> event loop is waiting for an event or timeout then your outer while loop
> will not cycle. Use the hightlight execution lightbulb on the diagram to
> see what the data flow is doing.
>
> Mike Sachs
> Intelligent Systems
>
> "Cheng" wrote in message
> news:[email protected]...
> > I put an "event structure" inside of a while loop. My target is to keep
> the
> > VI running and make selections to run different subVI. But I got two
> > questions:
> >
> > 1. how to use two button on front panel? I mean, when I press one button,
> > step 1 runs, when I press the other button, step 2 runs. Is event
> structure
> > the best way to do that? another side quesition is that how I can make the
> > button jump back after I pressed it? It kept in the "down" position and I
> > have to press it again to release it.
> >
> > 2. When I test the VI, I found the while loop can't stop. The boolean
> input
> > of false won't stop the VI. I wonder if there is a rule that the event
> > structure must run at least once? or any other hidden properties I didn't
> > notice?
> >
> > thank you very much!
> >
> > cheng
> >
> >
Hi Cheng,
that's not quite the whole story. The event structure breaks down
into two types. Those that get actioned between the start of the event
(i.e. mouse down) and the result of that event (i.e. the button
registers true) which are filtered events, and the other type (like
mouse up) which occur after the event and the result of the event.
With filtered events you can modify the result of the event as it
happens. Whichever you choose to use, you need to do one of two things
to get the button to pop back up (setting to latch when pressed on
it's own won't work) - you can either read the FPTerm within the event
itself with this set to Latch when pressed, or (my prefered method) is
to use the CtrlRef that's available inside the event, and use the
ActiveX method Reset to Default. This way the FPTerm for the button
can be left somewhere else, and it's more obvious what the program is
doing at this point.
Your while loop is actually a do {} while loop, i.e. it must execute
at least once before it checks to see if it should iterate again.
Mike's suggestion of follow the hi-light execution is the best
solution.
Hope that helps
Sash.

Can you share FP Controls between different Event Structures

I'm creating a program that will either read real-time data from an VNA on the GPIB bus, or read a saved s2p (Agilent) file and analyze it. The FP consists of 5 graphs, and various controls which handle events like printing, changing filters, or exiting. on the BD I have a case structure controlled by an operator selection pop-up. I tried using the same FP controls in the event structures I have setup in each case, as only one event structure would ever be executing at any given time, but the program doesn't seem to like it ast run-time. I've worked around the issue by creating "duplicate" controls and using the property setting to make them visible/disabled, etc., but the is seriously congesting my BD.
Anyone know a way to share controls with seperate event structures?

It sounds like the root problem is the overall structure of your program. I highly recommend that you check out the Queued Message Handler project template in LabVIEW 2012, that will show you how to utilize a single event structure and pass events to a consumer loop. If you program is too large to consider an architecture change at this stage of the game, then there is a workaround for your problem.
What is most likely happening is that you have the event structures all set to lock the front panel until the event completes. However the case structure that you have wrapped around these event structures is causing all but one of these event structures to be unreachable thus preventing you from handling the event. Again, as I stated above, the "RIGHT WAY" to fix this is to select a better program structure but the "kluge work-around" fix is this: Dynamically register for the value change event on all of the controls you are trying to trap events for. Dynamic events can be deregistered and re-registered at run time. This will allow only the event structure in the active owning case structure to be registered for the events, thus no other event structures will get in your way.
Disclaimer: This advice is given based on very minimal information and a great deal of speculation and may not be correct. Please include your code if you need further assistance.
Charles Chickering
Architecture is art with rules.
...and the rules are more like guidelines

Event Structure need to reset?

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