Event structure in a project using RT target

Hello.
As i was already told, i can't use dynamic events on RT targets. Can you suggest me a solution?
I have the following project:
Not a Real-Time Project. But project that using RT target: NI cRIO 9074.
My main VI looks like (part of it):
It is implemented by while loop, which runs until START button is pressed. The button pressed after all the values are set, and then the scan begins.
When i was developing this VI outside the project, I used event structure for save to new/existing file, show graph buttons (the white buttons). Because it should not interrupt the while loop (user can make setting, then press show graph, then set something again and only then press START).
It was like here:
Now, i wanted to bring all the parts together and put that VI in the project. In addition i wanted to add few buttons, like <-- and --> which are moving the motor manually before the scan starts. BUT, it didn't work.
Now I'm stuck
How can I implement what i describe above in my situation?
Thanks!!!

Hi Tacchi,
Are you planning on running your application as a startup executable or from the development environment? If you are planning on running this from the development environment, probably the closest thing you will get to the behavior you currently see with an event structure is by polling the value of the control that you wish to trigger the event. For example, if you wanted an event to be triggered when a button is clicked, you can have a while loop with a case structure inside of it that performs whatever code you want when the value of the button is true:
Granted this is not the ideal translation, but since RT applications are meant to run headlessly without a front panel, it may be the best option for your application.
Hope this is helpful!
Aaron P
National Instruments
Applications Engineer
http://www.ni.com/support

Similar Messages

Event structure in RT project

Hello.
In my main VI i have an event structure for few buttons. When I run the VI itself it works perfect.
When I open a new project, adding cRIO 9074 as a target, then adding the VI to the project the buttons doesn't respond. The event structure doesn't work.
Why? Is there any problem using event structure with RT targets?
Thanks

Tacchi,
Front panel events do not work on RT targets. Only dynamic events are allowed on RT. The reason for this is that when a VI is running on RT, its front panel doesn't actually exist. See this KnowledgeBase for more info:
http://digital.ni.com/public.nsf/allkb/42B70D2D0C4B568586256E2F0051441D
Chris M

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 .

Extent of Coding inside Event Structure cases

Hi all
I am trying to understand the practices while using an Event Structure. I am used to developing most of my projects using an Event driven State Machine Architecture. Most times, I use Event driven-Queued State Machines. I have also used Producer Consumer Architecture with Event structure driving the producer.
I have always believed that using lots of code, or lots of sub-vis inside one or more cases of an event structure is not a good practice. I reasoned that it will delay the capture of other events occuring while the current case is still executing. This was one of our points during design review, i.e., to reduce the code inside event strucutre cases to as minimal and necessary as possible. We used clusters/queues/LV2Gs inorder to pass on the required data, which will be processed in the other cases/loops.
However, I happened to recently come across a couple of very old applications upgraded to LV2011. The applications used an event structure in one of the while loops, with one or more parallel while loops inside the Main VI. The event structure was the only code in this while loop, no case strucutres.
These event structures had loads of code in each case, with sub-vis and nested sub-vis, even DLL function calls among them. Thats when I started to look for information on best practices using event structures and about any available details on the extent of coding allowed inside an event strucutre.
One sub-vi which was called as a dialog box also had its own event structure (ending up as ensted event structures). I have read about nesting event structures and their disadvantages.
Off course, the code is working and I am not sure if anyone had any execution problems with the applicaiton.
However, I am wondering about the pros and cons of having the entire code inside event structure. I would have defined that code a nightmare. Its disturbing me to see that code and being unable to make it better.
To my understanding, I wish to know if there is any definition or rule regarding the amount of code inside an event structure.
Thank you

The exception I use is User driven intefaces where every user action must get a response and each change must complete before the next. In those cases an event only implelmentation is generally fine.
Now if that code does something that takes long enough for the user to question if the program is still alive should at least get a "Busy cursor" OR a progress bar OR an abortable progress bar where the user get s the option to abor out. THe last case may warrent a parallel process to crunch the numbers.
But please keep in mind the above suggestions apply only to those User only" type things. Applcations that invlove the word "while" will generally get deamons and other common design patterns used to henld the implementation. But now I have drifted to design teory and away from the subject so ...
Have fun!
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

Event structure freezing when short delay inserted

Well, the simple stuff in LabVIEW I can do, but I'm still struggling to get my head around the concept of "Events" and how LabVIEW handles them. If I only have one type of event (i.e., pushing a button out of several on the UI, or reading a serial input and handling it programatically), I think I'm good. But my application requires me to be able to handle either of these at the front panel.
Going through the LV Knowledgebase got me this link (it's a little old - LV8.6, but seemed to handle the basics), from which I downloaded "events.vi" (attached). My situation is a little different, so I modified it a bit to "EventExperiment.vi" (also attached) to have a bare-bones template I could use for my application. If I run it as shown, it seems to run fine (with a serial input, the "1" and "2" lights turn off, but the Bytes at Serial Input indicator always shows "0" and the "Serial Indicator" light never lights - I am assuming that these change and revert too quickly to see in the UI). My concerns with my VI are:
If you add a short delay in the processing of the serial input event (say 1 second delay in that event case, or even a 1 second delay subVI after the serial flush connected through the error line), the VI accepts no further UI input after the first serial event.
If you add an error wire through all the events subVIs (whether you merge this wire with the one going through the serial subVIs, the program just hangs up.
And, one little bothering thing is that the original "events.vi" takes three presses on the "stop" button to close. I'm figuring here that it's because of those local variables being passed between loops, but it hasn't been enough of a bother to worry about.
Your help is greatly appreciated,
Cameron
To err is human, but to really foul it up requires a computer.
The optimist believes we are in the best of all possible worlds - the pessimist fears this is true.
Profanity is the one language all programmers know best.
An expert is someone who has made all the possible mistakes.
To learn something about LabVIEW at no extra cost, work the online LabVIEW tutorial(s):
LabVIEW Unit 1 - Getting Started
Learn to Use LabVIEW with MyDAQ
Attachments:
events.vi ‏24 KB
EventExperiment.vi ‏25 KB

Well, I thought I'd add a final post for some closure to this one.
To summarize what I was trying to accomplish: I wanted to have some kind of an event structure where you could use both regular User Events (button pushes, numerical control changes, etc.) and an outside (non-keyboard/mouse/touchscreen) event, like a serial character coming into a COM port, to initiate an action. This was to eliminate a loop where the computer would be polling the COM port continually at a pretty fast rate. (I must have read a hundred times in the past month that you don't want to run a While loop for polling if you can help it.)
It turns out (after a couple of confusing days, I talked with the NI service engineers) that you can't do this. In order to detect a character at a COM port, you have to be polling the port periodically with a Read and look for a change in the bytes available or another parameter. You can do this through a timed loop separate from your Event loop or through a Timeout event case inside the loop, like Don_Phillips suggested.
However, I believe I'll go the separate loop route, since my head's actually more comfortable with it than the Timeout route.
Thanks, folks, for your help,
Cameron
To err is human, but to really foul it up requires a computer.
The optimist believes we are in the best of all possible worlds - the pessimist fears this is true.
Profanity is the one language all programmers know best.
An expert is someone who has made all the possible mistakes.
To learn something about LabVIEW at no extra cost, work the online LabVIEW tutorial(s):
LabVIEW Unit 1 - Getting Started
Learn to Use LabVIEW with MyDAQ

Handling DAQmx Sampling Rate within Event Structure

Hello all,
I've been programming in Labview for a while now, but have recently been introduced to Event Structures. They are useful, however I think in the program below, the event structure is causing me trouble.
VI (Written in Labview 8.0): http://myweb.dal.ca/~jwoodacr/Pendulum.vi
The program itself is fairly straightforward, and by no means complete. One event allows the user to acquire data in real-time (Preview Data Event), and uses the Wait VI to control speed (I know this is not particularly accurate, but the preview does not have to be). The other event is meant to collect data with a well defined time interval between data points.
The problem is, I can press the "Collect" button once, and the "Collect" event will run fine with the values of "Time to Collect" and "Data points / sec" that were input by the user prior to pressing Collect. But, if one wishes to press collect again, no matter how you change the "Time to Collect" and "Data point / sec" controls, the express VI "DAQ Assistant 2" will only remember the very first values you gave it, and will output data with these parameters. So, if you change "Time to collect" to from one (1) to two (2) seconds after having run it initially with one (1) second, it will continue to remember the one (1), and collect data for only one second.
I've attempted to replace the express VI with all the proper DAQmx VI's used to collect in an identical fashion, but those also do not update past the initial conditions that are set. If you enable "Highlight Execution" and watch as the task proceeds, the numbers that are sent to the "DAQ Assistant2" VI are all as they should be, based on everything input on the front panel. It simply seems to ignore them upon execution.
This seems an odd problem, but I am hoping someone may be able to shed some light on it, or has experienced something similar in the past.
Thanks in advance.
Cheers,
Jeff

The DAQ Assistant only initializes the first time it is called. Thus each subsequent call, it does not care about the inputs into it. Another option is use DAQmx VIs and use a property node to modify whichever propreties you want. You must stop the task before changing its properties.
Brian R.
District Sales Manager
Washington DC
National Instruments

How to run the two events at the same time by using event structure

In my project, I have to run two stepper motor which can run both forward and reverse direction by changing the control in front panel so I am using event structure. In front panel I gave two separate controls for both stepper motor such as forward,reverse and stop. I would like to do motor1 will rotate alone, motor2 will rotate alone and both motor will rotate at the same time when user click the control in front panel. My doubt is how to run a motor2 while motor1 is running at the same time please tell me the suggestion for this problem
Attachments:
motor.png ‏192 KB

How do you control your motors?
Most motion control systems do supply two modes:
a) position based motion: The motion axis has a positioning system (most often some kind of encoder system) which enables the motion control to know where the axis is currently located. Passing the target location to the controller will result in the axis to move to that location. This is, for most applications, the recommended approach. It does require some sort of motion controller device.
b) direction based motion: This essentially tells the periphery device for the motor to move at a certain speed into a certain direction. As it does not stop at a dedicated location, it induces great risks for many applications if there are no kill- and/or end-switches. Depending on the setup, this can be either done with motion controllers or pure by software control (e.g. "controlling" the voltage level for the motor).
If you go for a), there is not much preventing parallelism as you request.
Option b) depends on the setup. If you have a control loop in the software itself, you have to move to an architecture like the producer/consumer. Please note that this does not incorporate any security measures for the external devices.
hope this helps,
Norbert
CEO: What exactly is stopping us from doing this?
Expert: Geometry
Marketing Manager: Just ignore it.

Can I use an event structure within another event structure

Hi
Can use an event structure within another event structure?
Thanks
Yasamin
Solved!
Go to Solution.

I attached my Vi from my old project (MY OLD VI). It is worked correctly.
But I decided that use event structure instead of case structure.
I attached my new VI as a picture and as a LabVIEW VI too (network_analyzer_8510_920527 Frequency Sweep.vi )
My graphs show by pressing "case 5: button (Bottom of page right hand).
Then I want to show each of graph in a large window( in a new VI) by clicking a key (for example "show 1").
Thanks
Yasamin
Attachments:
my VI.JPG ‏256 KB
network_analyzer_8510_920527 Frequency Sweep.vi ‏72 KB
MY OLD VI.vi ‏69 KB

Exit from the application using event structures

Hi
In my project i used event structure it working fine.
Now i want to exit(close) the application when i press EXIT button on the front panel.
Here i attached my project give an idea.
Regards
hari
Solved!
Go to Solution.
Attachments:
Sledge.zip ‏40 KB

Hi SAM
U saw my ok.i have one more problem when i run the program(main vi) all the remain sub vi's also opened.
i want open sub vi when i press a button on front panel.
i have made small changes to it.
Regards
hari
Attachments:
Sledge.zip ‏41 KB

Using multiple events structure inside state machine to control the Tab

Hi y'all,
Anne here.I have a Tab indicator in my front panel and I want to be able to control the flow of my program based on what controls I clicked inside the tab. I am using a state machine architecture and inside every state, I use an event structure to check for user interaction to determine the next state and what tab page is going to be displayed next. This means that I am actually using multiple event structures in my application and I use them in just one while loop, but just that they are not running in parallel since I am only using "one event structure per state" which means that only one event structure is running at one time. My questions is, programming technique wise, am I doing it correctly? So far, I am not facing any problem (I am still in the early stage of the project) but I want to check with you all first on your opinion regarding this architecture. Will there be any issue on using multiple event structures in a vi? Since I will be using a tab, and the controls available in the tab will be the controls that will control my event structure for that state, by right, there should be no issue. Am I correct to assume this? Is there any limit on the use of event structures? I have attached here a simple sample of the architecture that I am talking about for your reference. I have attached a 2010 version and a 8.6 version. Let me know what you think or any opinions that you may have.
Hoping to hear from you soon! Thanks so much in advance!
Cheers!
Anne
Attachments:
State Machine-Event Structure Sample_2010.vi ‏19 KB
State Machine-Event Structure Sample_8.5.vi ‏25 KB

Hi jak888,
I decided to use tabs cause I don't want to have subvi pop ups every time i need to perform the process in the state and show an update in the front panel. This is actually going to be more of an ATE where you will have to choose first whether the one using is the operator or the engineer. If the operator is logged in, she will proceed to choose what test to run (this state will have its own event structure). This part, I don't want a pop up, so what happens is that from Login page, if the user logs in as operator, the tab will automatically switch to the Test Selection page. After selecting the test, it will proceed to Start Test state and the tab will show the Result Summary page. If the user logs in as engineer, then a totally different tab will be automatically shown next and so on. By doing this, I will be able to show an update on the front panel objects without having the subvis pop up. I will also just need to use the call reference functions to call my subvis, making my Main VI more generic. The tab Page header will be hidden so the operator will actually not see that there is a tab and that there are a lot of controls and indicators cause they are hidden in the tabs and that page will only be shown based on what they selected from the main tab.
I appreciate your thoughts! thanks so much!

How can I determine whether to use an event structure or a case structure?

I'm starting a large project and need a state machine. I can't decide on whether to use a case structure or event structure. Is there an article or other information that describes criteria for selecting between the two approaches?
Thank you,
Chuck
Solved!
Go to Solution.

Hi Chuck,
Well case structures and event structures differ quite alot. Here's a link for indepth information on Event Structures, and using them in state machines: http://zone.ni.com/devzone/cda/tut/p/id/2962. Hopefuly this will help you make up your mind.
Let me know if you have any questions after reading it.
Regards,
Dominic Walker
Cardiff University
Electrical and Electronic Engineering Student

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 .

How can i use the same front panel graph in more than one events in an event structure?

i want to display the signals from my sensorDAQ in a graph.but i have more than one event in the event structure to acquire the signal and display it in the graph.the first event is to acquire the threshold signals and its displayed in the graph as a feedback.after the first event is executed, i will call the second event,where the further signals are acuired and compared with the threshold signals from the event 1.my question is how can i use the same front panel control in more than two events in the event structure?please answer me i'm stuck.
Solved!
Go to Solution.

Hi,
I have attached here an example of doing the same using shift registers and local variables. Take a look. Shift register is always a better option than local variables.
Regards,
Nitzz
(Give kudos to good answers, Mark it as a solution if your problem is Solved)
Attachments:
Graph and shift registers.vi ‏12 KB
graph and local variables.vi ‏12 KB

How to use a event structure with a state machine

First, I would like to inform you that I only work on LabView part time, and have much to learn. Anything I do learn, I usually forget until I need it again, because I only work on it part time.
Using your StopWhileLoopMOD[1].vi, I am trying to put a state machine inside the event structure.
Related link: http://forums.ni.com/t5/LabVIEW/How-to-stop-while-loop-in-Event-case/td-p/465564/page/2
Here is my application: on the front panel, the user can select any combination of 7 different tests. I have created cases to perform each step of each test in the correct order, but if the user presses stop, the tests won't stop because some of the cases have a while loop inside the event structure (like you mentioned is a bad idea). The user should be able to stop the test, reselect tests to perform, and re-start the tests.
When the start button is pressed for the event structure, I need all the cases to run in the proper order, unless stop is pressed.
In the past I have indexed an array and used that to run the state machine, but it won't stop immediately.
I have sub VIs that are built in while loops because the outputs of the product needs time to stabilize.  The state machine stops and waits up to a certain number of iterations. If it passes the test, the while loop stops and the next state starts. If it takes too long, it exits and reports an error. Maybe I need to just use the state machine and not an event structure?
Is there a good example of an event structure?
metzler CLAD
Solved!
Go to Solution.

I'm not sure exactly what you are asking, but it sounds like you want to script a bunch of tests and if the user says stop, to immediately stop the current test and abandon the others? I'm going to assume that you know how to clear the array so that it will abandon the others, so I'm guessing that you are having trouble abandoning the current test? If this is indeed the case, then the problem is that you are not able to propagate the message from the main VI FP which is the GUI to the sub vi which is the test, where the test may or may not have a GUI (FP visible) of it's own. Threading was the first thing to come to mind, but this may not be necessary using events.
You can do this by passing a refnum of the stop button to the subVI, where you can then add that wait to the event case structure.
I've attached 2 VIs, mainvi.vi which is just a loop displays the count*2 (number of seconds passed since running) that will call subvi.vi and then check to see if the stop button is pressed. mainvi.vi is by no means a state engine, it is just a simple loop for demonstration purposes. subvi.vi just waits 2 seconds and leaves, it is a better structured state engine with an init state to start a poll case to wait for events and an exit state to clean up. You can modify this any way you wish to get it to do what you want. You will note that even if subvi.vi is being executed, it will terminate immediately when the stop button is pressed.
Hope this helps.
A
Attachments:
mainvi.vi ‏17 KB
subvi.vi ‏33 KB

How to use an Event Structure responding to an image control that belongs to a parent VI.

Hi
I am loading a subpanel vi by pressing a button located in the user interface of the main vi which also contains an image display. Subpanel vi opens up on the side and doesn't hide the image display of the main vi. Subpanel vi contains an event structure that needs to respond to user clicking on the image display of main vi.
Since the bug that occured while creating an image reference control isn't fixed, I am passing the main vi pane reference onto the subpanel vi. From that point I've tried to edit event structure and have it respond to the image control/pane that belongs to main vi but I don't know how.
Any help would be appreciated.
Thanks

Post a screenshot of your subVI code where you register the events.
André
Regards,
André
Using whatever version of LV the customer requires. (LV5.1-LV2012) (www.carya.nl)

Event structure in a project using RT target

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