LabVIEW Event Structure only accept user action?

Hi All.
For example, Event Struture responses to a 'BOOL Control' such as someone press the button.
But, if I use property node to change Bool control status, Event Struture can not accept such a action?
Why?
Any solution for monitor variables and controls change which is not caused by user actions.
*The best Chinese farmer*

You can use the value signaling property node, if you want to go down the property node route. The best way would really be using user defined events and wire these events to the dynamic event terminal on the border of the event structure. You can check out the examples that ship with LabVIEW to see the VIs that you would need to accomplish this task.
Hope this helps.

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Event case with non-user action

Hi
I'm actually using LV8.0.1.
With this and older version of LV it wasn't possible to get an event case fired without an user action. (for example by changing the value programmatically.)
Is it possible in LV 8.2?
Regards
Yves

Yves,
You just missed the property node in your right-most loop. To create a property node, right click on the block diagram control->create->property node, and then select "Value(Signaling)". Value(Signaling) is different from "Value" in that it "signals" to LabVIEW that a change has been made, and thus an event can fire. See the image of the code in your right-hand loop.
Hope this helps!
Message Edited by Day on 10-11-2006 09:29 AM
Attachments:
Value Signalling.jpg ‏6 KB

Using an event structure to register many actions

Hi there,
I'm making a simple game;
4 player game.
Each player gets a led that flashes at random and a button to hit when the LED is on. But it is only on for 500 milliseconds.
I’m having troubles with it. i think i need a case structure in the 3rd case of the main case structure?
at the moment points are awarded if the button matches the LED. i.e. both on or both off.
Any help is appreciated
Attachments:
buttonbash v1.vi ‏17 KB

First, let's clean up some of the Rube Goldberg code.
(You don't need a case structure to output a True or False boolean. Just use the condition.)
As for your code, I don't know where to help. You talk about an event structure, but there aren't any in your code.
Attachments:
buttonbashV1.vi ‏12 KB

Weblogic.xml only accepts users as principals?

I've got a custom security realm with several users and groups in WLS6. I'm trying
to make it so the "everyone" group is the principal allowed to access a webapp:
     <security-role-assignment>
     <role-name>everyone</role-name>
     <principal-name>everyone</principal-name>
     </security-role-assignment>
When I do this, no one can access the webapp (despite the fact that all the users
are members of this group). When I replace the everyone principal with an enumerated
list of users instead, login works fine.
So... why can't groups be used as principals?
Kill -nospam- to email me.

Hi,
The authenticate method would take the user and the password details from the environment
(env) that is passed and after successful authentication would populate the subject with
the principals (i.e user, group the user belongs to ..)
It should work with any user that is defined in the WLS not just weblogic/weblogic.
Do you have any other users defined and which group do they belong to?
Vimala
Khalid Rizvi wrote:
I am playing (learning) with weblogic.security.auth.login.UsernamePasswordLoginModule
as a LoginModule using JAAS based authentication. Surprisingly, the only userid
and password combination acceptable is uid=weblogic, pw=weblogic combination.
I went through and looked at the example code under
http://e-docs.bea.com/wls/docs70/security/cli_apps.html#1042212. I found that
the UsernamePasswordLoginModule.login calls into
if (url != null) {
Environment env = new Environment();
env.setProviderUrl(url);
env.setSecurityPrincipal(username);
env.setSecurityCredentials(password);
try {
Authenticate.authenticate(env, subject);
Seems like UsernamePasswordLoginModule only is a router, as it instantiates an
instance of Environemt using the userid and password and passes this Environemtn
instance (env) to Authenticate.authenticate along with the empty Subject instance.
I read about that the Subject instance will be filled in with Principals by the
WL Server.
My question is that firstly,
1. As Authenticate.authenticate is not passed in the uid and pw, will it pick
those from the env?
2. Secondly, why does it only accept uid=weblogic & pw=weblogic.
I will appreciate if some one can put me in the right direction.
Khalid R. Rizvi
508-641-1192
[email protected]

Labview event structure

hello
can anyone tell me why the terminal shown by circle 1 at the start of event structure is showing different from the circle 2 at the end of event structure
thanks
Attachments:
event.jpg ‏59 KB

This is a tunnel that has enabled the option "use default if unwired", this is the default option when working with the event structure.
http://zone.ni.com/reference/en-XX/help/371361G-01/lvscript/conditionaltunnel_use_default_if_unwired...
Jonathan Cruz
CHALLENGER
K U D O S __ B I E N V E N I D O S

Event structures in older versions of labview?

Can anyone tell me how to create a workaround for a 'value change' event structure in an older version of labview? I have a student version of LabVIEW 6i and need to create a queued buffer from each value change. Thank you.

James.Morris wrote:
Ah, you're only one release away from the event structure. That's too bad.
You're going to have to implement a Polling loop that continuously checks the user inputs. Make sure you add a Wait function to the loop (~100ms) because that will act as your chance for the user to make changes. You can use shift register(s) to keep the previous loop's values and compare to get a bunch of Value Change booleans. If you want a specific case for the specific events, then you can group all of your Value Changes in to an array and act upon the ones that are True via a Case Structure.
The Event Structure only pulls a single event per loop and has a queue of events to handle for following loops. You might encounter multiple value changes in a single loop if the user clicks fast enough, or you trigger value changes. To avoid losing the trailing events, you should probably have a For loop within the Polling loop that handles all True values. Either that, or have a consumer loop that handles all of your events.
James, I swear I'm not picking on you today
You can set the maximum number of events alowed in the event queue per event in the edit event dialog box. Check box and int fields in the lower right side.
6.i didn't have a "Value (Signaling)" property- (a subject of some CLAD exam questions not that you suggested it)
Student editions could not use 6.i events. From 7.0 or 7.1 through 2011 Student Edition could use but not edit event structures. 2012 and on Event Structures are available in "All Versions" of LabVIEW- at the time. I haven't looked into the newer license options.
On to licensing options. (Not a lawyer! consult your Legal Dept!)
If you are not doing work towards earning a educational certificate you should not be using Student Edition. And, in some cases (Like working on a student project with commercial investment) not even then!
The Home Edition is also a new option. It is intended to enable fast "Proof of Concept" development or development for your sole non-comercial use.
LabVIEW Full and Professional are for comercial use and have a "Home Use License Agreement" clause attached. If your company owns a LabVIEW License you CAN install a copy on a "Home PC" for the limited use of aiding your employer (who paid for the license) such things would arguably enclude "Training"
NI is not totally opposed to negotiating "Exceptional" agreements for mutually beneficial reasons. Youl'd better bring a justification better than "I can't afford it" Go find some investors and buy a license in that case. And Yes, until the moderators take this down, I did at one time have a LabVIEW license for exclusively engaging the LabVIEW Community (Forums and NI Sponsored events use only- LAVA was not encluded) I'm not sure if such a deal could be negotiated in the future. In Fact, The Home Edition would have been less costly.

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 .

Event structure doesn't register local vars

I have a gif of a basic FPGA topology that I want to show some loopbacks in. As the user clicks on the booleans, vertical lines should appear, then disappear as they click them again, showing the current loopback topology.
To conserve resources, I opted to use an event structure. So far I have set it up for the RX_FAC and RX_TERMXCO4AU loopbacks that you see in the upper left of the picture.
Only one RX loopback and one TX loopback can be on at a time, so one of the first things that happens when the user clicks the boolean is that it sets the values of all the other booleans in that row to false, via the use of local variables.
The problem is - the event structure only executes when the user actually clicks the boolean true or false, but not if the boolean is set false via the use of a local var. In other words, let's say I have RX_TERMXCO4AU true, and RX_FAC false. If I click RX_FAC to set it true, then you'll notice RX_TERMXCO4AU goes dark/false, and RX_FAC lights up. So the value of RX_TERMXCO4AU changed, but the event structure associated with RX_TERMXCO4AU did not execute (which is why the vertical line between RX_TERMXCO4AU and TX_FACXCO4AU stays there).
This will make a lot more sense if you run the attached simple VI. Right now, events only exist for RX_FAC and RX_TERMXCO4AU, but it's sufficient to explain the problem I think.
Any help is appreciated.
Solved!
Go to Solution.
Attachments:
loopbacks.vi ‏55 KB

bmishoe wrote:
I learned something new today...
One more thing you can learn, When you are passing an array input to a For loop with 'Auto indexing' enabled, you need not wire anything to For loop's 'N' terminal.
In other words:
If you enable auto-indexing on an array wired to a For Loop, LabVIEW sets the count terminal so you do not need to wire the count terminal.
In your code, you can remove the 'Array Size' nodes.
I am not allergic to Kudos, in fact I love Kudos.
Make your LabVIEW experience more CONVENIENT.

Event Structure Question

Hopefully I can explain this okay....
I'm using an event structure to control several features in my program and all have worked great. All of the events in my program are handled via boolean buttons with value changed option. I have a numeric control in my program that controls integration time. This changes when the user clicks the up or down arrow or types in a new value. This control is used and needed to changed the integration time in a couple of different event cases. However now I'd like to use this numeric control (integration time) to not only change the integration time but also trigger one of the events (in addition to the normal button that I have been using to trigger the event I need to have happen). (The value of the numeric control when changed also executes a case structure when it is changed in one of the other events.)
However when I tried to do this, I ran into some problems.  If I change the numeric control value during one of the events in which I need to use it, and after stopping the event, then another event seems to execute (based on the changing of the numeric control, this event is the same event I ultimately would like to trigger). Basically I need to stop the numeric control from executing after stopping another event when its value has been changed and only executing when I need it to. Everything I seem to be doing hasn't been working and I'm just not seeing any type of walk around. But I need to be able to use the control in various events to change the integration time and also if needed to change it and thus trigger an event (besides using a boolean button to trigger the same event).
If needed I can post screen captures or sample code, but my main vi is rather large, so I'd have to cook something up as an example.
Any help provided would be much appreciated.
Using Labview 7.0 and 2010 SP1 with Windows XP and 7.

The attached amusing example is an architecture which will work for you. Read the documentation for details. It has two components - an event hander and a task handler. The event handler is the LabVIEW event structure. The task handler is the queue-based outer loop. If you need to add data to the tasks defined for the queue, make the queue element a cluster and add a variant to it.
As a general rule, most UI projects involve getting to the same task through different events, making this the standard design pattern for almost any UI driven program. You can separate the task handler (consumer) and the event handler (producer), but I have found that the synchronization problems are not worth it.
I posted 7.0 and 7.1 versions of the code.
This account is no longer active. Contact ShadesOfGray for current posts and information.
Attachments:
LargeGUIApplicationsInLabVIEW_70.zip ‏735 KB
LargeGUIApplicationsInLabVIEW.zip ‏711 KB

Multiple event structures in one program

I know it's not good practice to have one event structure inside another event structure (I don't know exactly why). But if another event structure is in the subvi, is it safe? Please comment.

guangdew1 wrote:
I know it's not good practice to have one event structure inside another event structure (I don't know exactly why).
This is because of dataflow and the way event structures work. If you have an event structure inside an event structure, both event structures will accumulate events whenever one occurs, but it is unlikely that they can be handled in the order they occur or at all. By default, event structure are set to lock the front panel until the event completes, meaning that if an inner event gets triggered first, the code will lock up, because it will no longer be possible to trigger one of the outer events. If the outer event occurs first, it cannot complete, because it requires a later firing of one of the inner events before it is ready to handle the next event that occurs in the UI. Even if it marginally works if the panels don't get locked, you are requiring the user to trigger events in a certain order. How is he supposed to know what's allowed or not?
If this is not exactly clear to you, you need to start with a few tutorial and learn about dataflow, Then start using a single event structure and see how things work by programming scenarios and see what happens.
guangdew1 wrote:
But if another event structure is in the subvi, is it safe? Please comment.
Event structures are only useful inside interactive subVIs that show their front panel. even then I strongly advise against calling anything interactive, or anything that takes excessively long, inside a main event structure. You end up with code that can become unpredictable, can deadlock, is hard to debug and flies in the face of all good programming guidelines.
Obviously, you have some specific application in mind where you think something like that is useful, I can guarantee you that there is a much better solution is you think about this a bit longer. If you need help, please describe exactly what the program should do and how it should react to user interactions at the various stages.
A program should always be approached from the code and UI needs. Don't start with a harebrained code construct (events inside events) and then look for a use. It does not exist!
Event structure only belong in toplevel loops. They should never be hidden insde squences or case structures (or other event structures as already mentioned above). If you have multiple toplevel loops that run in parallel, it is safe to place up to one event structure inside each. Each event structure can have an unlimited number of event cases. This should be sufficient to handle any programming need you might have.
LabVIEW Champion . Do more with less code and in less time .

How to control the tab control using event structure?

Hi,
I am using tab control and event structure in the program.
When i run the application event is not happening for the active page.
When user switches from active page to the other page then event is taking place for all pages
So, how to get the event trigger for the active page when the application is started
For more clarification i am attaching the code "Test Control Tab using Event Structure.vi"
Attachments:
Test Control Tab using Event Structure.vi ‏52 KB

You have a basic misunderstanding of dataflow. Maybe you should start with some tutorials or study some of the examples that ship with LabVIEW.
The event structure belongs inside the while loop, and not vice versa. RIght now, the event structure only runs exactly once and never again.
If the stop is pressed first, the VI will stop. Game over.
If the tab control is changed (from any state to any other state!), the inner loop will spin forever as fast as the CPU allows, either executing one or the other case. It just reads the tab terminal to decide which case to execute. Changing tab never triggers any events. The VI is trapped inside the event until stop is pressed to stop the VI.
you were closer to a reasonable program in the other thread:
http://forums.ni.com/ni/board/message?board.id=170&view=by_date_ascending&message.id=287905
Have you tried execution highlighting? Maybe things would become more clear of you do.
LabVIEW Champion . Do more with less code and in less time .

Does the Event Structure work with cRIO?

Basic question, I know, but I did search. Honest! LabVIEW lets me drop an Event Structure in code targeted for cRIO, but so far it's not working. Is there a secret? Or is it that event structures don't work with cRIO? TIA!
Jeff

Jeff,
According to these two NI documents, RT targets support the Event Structure only with dynamic events.
http://zone.ni.com/reference/en-XX/help/370622F-01/lvrtconcepts/rt_unsupportedets/
http://zone.ni.com/reference/en-XX/help/370622F-01/lvrtconcepts/rt_unsupportedvxworks/

Event structure-Plese help

I have made a GUI for communcation between two pc with various parameters.
I have used an event structure for 1st PC because i have 3-4 parameters which i want to run as i press the boolean on front panel.
However my problem is suppose I press the 1st boolean, I want the 2nd pc to receive and respond that data has been received. And since there are 3-4 parameters, i will have to use event structure for 2nd PC too. But there will be no one to control front fanel of 2nd PC.
So, how do i do it. Any alternative to event structure in which it resoponds to data recieved and not on user input.
Thanks.

In my experience with serial communications, you will want a loop for nothing but reading from the port. You can use a global or a Notifier to tell this loop to stop. You will want a second loop for GUI and message handling. So I encourage the use of the Event Structure here, using User Events to send the commands/data to this loop. Then you will want a third loop for sending commands through your serial port. Send the commands/data to this loop using a queue.
So the process will go like this for PC-2:
1. Read command through serial port. Serial Read loop sends this message to GUI loop via User Event.
2. GUI loop processes user event, does whatever is needed, and sends the response to the Serial Write loop via a queue.
3. Serial Write loop reads the message to send from the queue and writes it through the serial port.
There are only two ways to tell somebody thanks: Kudos and Marked Solutions
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Problems closing several loops in a state machine with an event structure

I am having some problems closing three loops running in parallel in a state machine. I have one loop for an event structure to monitor user controls to change the state. The other loop is the state machine which will control an actuator, and the third loop is for data aquisition/analysis. I want to be able to hit the stop button and go to a "shutdown" state where I can home the actuator then close the loops and finally go to the last "shutdown" subdiagriam in the flat sequence structure. Currently when hitting the stop button it goes into the shutdown state and will end the state machine loop but it appears the other loops are not closing until I hit the stop button again. Could this be due to using a local variable for the boolean to control the loop conditions? I attached a screenshot of the block diagram. Any advice would be great!
Attachments:
example.png ‏108 KB

You have a classic race condition due to overuse of local variables. If the stop event fires in the upper loop, the local variable connected to the loop termination condition has already been read (it is false!). This means that the upper loop will iterate once more and again wait at the event structure for the next event. At this time, the local variable connected to the loop termination is TRUE, but the loop cannot complete until the event fires again, for example if you press the stop button once more.
The correct way is to connect the terminal of the stop button across the right event frame directly to the loop termination terminal. Now it will get the TRUE value correctly once the stop event fires for the first time.
LabVIEW does not execute left to right, execution order is determined by the wiring.
I also agree with the above message that you should rethink and re-architect your code using established coding guidelines.
LabVIEW Champion . Do more with less code and in less time .

Can not use Global Variable in Event Structure

I am using LabVIEW 2009.
In my LabView project I have a Boolean Global variable called EStop. I can read and write the Global variable. If I double click on the Global variable, it takes me to EStop.vi which includes a Text Button. EStop.vi is part of my Project.
In one of my VIs, I have an Event Structure. If I go to one of the Event Handlers in that Event Structure and right click and then select Add Event Case, I get a list of possible events. But that list does not include EStop or an EStop events.
I want to Add an Event Case for EStop: Value Changed.
Why can't I Add events to an Event Case that include events on Global Variables like value changed?
How do I add EStop: value changed event to my Event Structure.
Solved!
Go to Solution.

dbaechtel wrote:
I have many events throughout the system that might need to cause the system to do an Emergency Stop action. So I want ro use a Global variable that is accessible from anywhere in the system. Any action or condition that occurs anywhere in the system can activate the emergency Stop condition by setting the boolean EStop Global variable to True. When the Global bolean variable goes true(value changed), I want to detect that event in an Event Structure and do the actions necessary to accomplish a system Emergency Stop.
Sorry, I am not familiar with your terminologies. What is your definition of a "system".
One big VI with many parallel loops?
Several VIs running in parallel?
LabVIEW Champion . Do more with less code and in less time .

LabVIEW Event Structure only accept user action?

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