Trigger Event Structure Case on Startup

Hello,
Within my project, I am controlling a linear actuator via Modbus TCP, with an event structure within a loop. I control its velocity, acceleration ... etc. It works beautifully, but I must change the values of the mentioned parameters to trigger the event cases, after startup. I would like to trigger the event on startup of the program and take the current values on the front panel.
I have heard about "Property: Value(Signaling)", but I cant seem to understand it and how to implement it..
Any guidance and help would be appreciated!
Thanks,
Danny

It won't work for you because you already have something designated for the timeout case, and you want a different event case than that to run on startup.
But, here is the explanation.
At the top left of the event structure is the timeout terminal. The number you wire in there tells how frequent the timeout case could execute. If you put a 0 constant outside of your loop and wire it into that terminal through a shift register, it will execute immediately or almost so. After the event structure, wire a -1 into the right hand shift register. Then after successive iteration, the timeout case will be disabled.
Attachments:
Example_VI_BD.png ‏12 KB

Similar Messages

Passing values between event structure cases

Hello everybody,
I have a question concerning the event structure - how to pass values (let's say a string / the state of a boolean control / the value of a numeric control value / an array of numeric values) between event cases ?
There seem to be 2 situations here :
- when you need to pass the value of the control that triggers an event;
- when you need to pass the value of a control which is modified in an event case.
I have read the documentation but i still do not understand very clearly how to do this. Maybe you can point me in the right direction (maybe some threads on the forum that i have missed).
Thank you very much !!
(KUDOS for everyone who is interested in this )

AndreiN2014 wrote:
- when you need to pass the value of the control that triggers an event;
- when you need to pass the value of a control which is modified in an event case.
The first question isn't worded very well. What exactly are you looking to do? Are you looking for an event that specifically relates to that control? If so, just drop it inside of the event and wire it. Are you looking to trigger multiple events from the same control? Ie, you hit the control, event1 is triggered which then triggers event2 ... ? If so, you might consider taking a look at a different architecture. I can think of very few cases where I'd prefer do this over something like having the button trigger a state and using the state machine architecture.
Others have pointed out the Shift Register. This is the typical way to pass values between one iteration of a loop to another. We can assume you have some sort of loop outside of the event structure to make it run a second time. Put a shift register on this loop and the value wired into it will pass each iteration. But, if it's just a random control, you can also just leave that outside of the event structure and wire it in as well. This will provide the new value to the next occurrence of the event structure.
You really need to define your problem before trying to solve it.

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

Trigger Event Structure in SubVI

Here's my goal. I have a VI that sets two analog outputs which in turn control a power supply. One output controls voltage while the other controls Current Limit. I created a VI which uses an event structure so that when the voltage or current limit is changed, the analog outputs are adjusted accordingly.
Now, I'd like to turn that into a SubVI and have it running in the background while my main VI runs. I'd like to be able to go into the subVI and change those values at certain locations within the main VI. I tried just using the subVI with register events, but it hangs because it is waiting for the subVI to finish before continuing. I tried using the Run VI methond with "wait until done" set to false, but then I don't see how to trigger my events because I can't link my mainVI to the events that need to be triggered. I can set the control using Control Value Set, but that doesn't do anything for my event structure and thus stuck again.
Maybe the event structure isn't the best way to do what I'm seeking. But I don't want to set all this up in my Main VI because it just adds too much complications and I already have the VI working by itself and just want to turn it into a subVI.
Thanks.

You could either get a reference to the SubVI and find the specific control like the attached picture, or you could pull the SubVI out of the main loop. If the SubVI is necessary for data flow, you are almost certainly going to have a hang up if you don't call it by reference.
edit - Another, probably less popular, option would be to have the subvi running in a parallel loop and have locals take data from the control loop and write to the command loop. You'd have to be careful to only have one local writer, though.
Message Edited by JeffOverton on 01-30-2008 02:39 PM
=============
XP SP2, LV 8.2
CLAD

Event structure, case structure, iteration number

Hi
I am trying one example about Event Structure from the book, LabVIEW for Everyone: Graphical Programming Made Easy and Fun.
The example in the book looks like this:
The number of 'work done' equals 'iteration number'.
But when I build a Vi and try this example, I got this:
iteration number is two times the 'work done'.
I have attached my Vi. Does anybody know what's wrong with my Vi
Thanks
Bing
Solved!
Go to Solution.
Attachments:
do some work.vi ‏10 KB

Both Activation and Deactivateion of the boolean causes Value Change events, but you only add 1 when it's activated. If you set the booleans mechanical action to Latch instead of Switch they should be the same.
/Y
LabVIEW 8.2 - 2014
"Only dead fish swim downstream" - "My life for Kudos!" - "Dumb people repeat old mistakes - smart ones create new ones."
G# - Free award winning reference based OOP for LV

First event fired to event structure

Hi all,
Does anyone know what's the first event being fired to the event structure on VI startup? I set a breakpoint on the event structure and it breaks. However i wasn't able to capture whats the event.
My intention was simple; i have a table which list all the IO names and values. So during VI startup, i wan to populate the IO names first. Then in a timed-loop, the values are updated respectively. In this case, i don't need to "refresh" the table every time which waste time and resources.
It something like the OnLoad event.
Another way out is to register an user event, and have this event fired during application startup. But i wonder if anyone has a better way?
Many thanks!

j3r3mi wrote:
My intention was simple; i have a table which list all the IO names and values. So during VI startup, i wan to populate the IO names first. Then in a timed-loop, the values are updated respectively. In this case, i don't need to "refresh" the table every time which waste time and resources.
Why don't you show us some code.
Are the IO name static for the duration of the program? Are you using a regular table column or the "row header strings []" property for the IO names?
If you want to write the row headers at the start of the program, place the code before the main loop containing the event structure. No event case needed. If you have a specific event to update the table headers if needed, fire the event once at startup using a signaling value property, again with the property node placed before the main loop.
LabVIEW Champion . Do more with less code and in less time .

Strange problems about my projects(efficiency,event structure,queue)

hey,guys,i am a labview user from china,so forgive me about the chinese words of my projest. i found something wrong with my work. .
there are two functions in my "While loop", the first one depends on "queue" and is to get information from UART, the second one is "event structure" to send information through UART. my problems:
1. i can not stop while loop by pressing "停止“, and i find two ways to stop it. first, i press"停止”,then, i press any buttons that can trigger "event structure"twice, at last, while loop can stop.the second way, i press buttons for "event structure" one time, then "停止”， and then the same button for"event". it also works
2.my work does not run efficiently. you guys can try. once you press buttons for "event structure", it responses very slowly,and if you press many times,the whole program seems like suspending.i have added a LED named test at the front panel, it should light once you press "运行“. and it also shows how slow the whole program is.
i have attached my work, and my main vi is "串口通信主VI".
can any body give me some suggestions? thanks a lot
Attachments:
Uart.zip ‏140 KB

Your event structure will execute exactly once per loop of the main loop, thus the other three loops must stop before handlig the next event. You will also get a race condition between the top loop and the events when writing.
I'd put the top loop as the timeout case in the event and place the loop around the event for starters.
/Y
LabVIEW 8.2 - 2014
"Only dead fish swim downstream" - "My life for Kudos!" - "Dumb people repeat old mistakes - smart ones create new ones."
G# - Free award winning reference based OOP for LV

How to Transition to a Specific Case from an Event Structure Trigger?

Can someone help me troubleshoot my program. I've attached my VI so you can follow along with what I am describing. So here is the scenario:
I have a program that consists of four test states, stop test, request test info, and end program (cluster of 7 booleans). Each test state sends a serial command to a DUT, receives ACK packet, opens relays which disconnects the serial connection and DUT will continuously test by itself. If the user wants the end the test early, they can hit the "Stop current test" which will close the relay reestablishing serial communication, wait 10 secs for device to enumerate on the PC, and then send the serial command to stop the test. From here, the user can request test information from the DUT by hitting the "Request info" button.
So my dilemma is when I try to implement a time limit for cases 2 - 4. For case "M1-Idle", the program works flawlessly since there is no time limit. The program will send the serial command, transitions to "Open Relay" case and switch back to the "Idle" state to wait for the "Stop" command. The user has to hit stop whenever to close the relay, request info and/or continue testing.
For case 2 through 4, there is max time limit of 3 hours. This is where I am having difficulty opening the relays and then entering the timer count down case structure to start the timer. Question is, if I am using the Event Structure to trigger on a user action event (i.e. user presses "Run M2-Normal" - Menu.M 2: Value Change) it sends the command and move on to "Open relay" to break the serial connection as intended. Since the next state of "open relay" is "Idle" how can I add case selector to select "M2 - Timer" instead of "Idle" given that it was based on user selection of "Run M2" event?
Is that even possible? I tried using the feedback node on the state enum but its coming from the case state and not the event state so it doesn't enter properly into the timer state. Any help or ideas is greatly appreciated. Thanks in advanced.
Main_Working_Copy.vi is the main portion of the program.
Best regards,
Henry
Attachments:
Main.zip ‏106 KB

Hi Ofek_zeevi,
Welcome to the Support Communities!
The article below explains how to gift a song in the iTunes Store.
Some songs are not available as an individual purchase.
iTunes 11 for Mac: Give music and video
http://support.apple.com/kb/PH12293
I hope this information helps ....
Have a great day!
- Judy

Event Structure Trigger Controller

Hi Everyone. I'm working on a motion control system for a flight simulator base using Labview. My code uses a while loop with a few case structures to constantly transmit data to a second computer where it is conditioned into base motion data. Currently, these transmissions occur in real-time: I cannot input three different commands and execute them at once.
I want to be able to input multiple different values into a seperate controller and "start" them all together. An event structure seems like it would be the perfect solution to my problem, but I'm having difficulty with the program timing out or receiving the wrong inputs, which causes some diasterous effects on the machine. Any help on where I should place this event structure, how to wire the inputs to existing controls, or any helpful tips are greatly appreciated.
Attachments:
HostControler2.vi ‏78 KB

1. Your event structure must be inside a while loop to trigger on more than just a single event. http://zone.ni.com/reference/en-XX/help/371361H-01/glang/event_structure/
In your VI the event structure will only ever fire once when you click "Start 2". Then it will never fire again.
2. Every control that you want an event to fire on must be registered and handled in an event case. They can all be in the same case, as long as they are registered in there somewhere.
3. Try to keep your block diagram on a single screen, it makes it easier to follow. (Unless your screen is actually twice as high and wide as mine?)
4. Try to keep all wires visible and all data flow from left to right, wires shouldn't be going backwards or behind objects etc. That will also make it easier to follow.
5. You are already using basic state machines, you probably don't need to have a while loop in a while loop.
6. If you need different actions performed asynchronously you will likely need more than one while loop (executing asynchronously, not nested) using queues to communicate between them.
7. Do you really need to continuously transmit data or only on change?
There's more but that should give you a good start.
Troy
CLDEach snowflake in an avalanche pleads not guilty. - Stanislaw J. Lec
I haven't failed, I've found 10,000 ways that don't work - Thomas Edison
Beware of the man who won't be bothered with details. - William Feather
The greatest of faults is to be conscious of none. - Thomas Carlyle

Can I have multiple event structures with the same event cases?

Hello,
I'm doing an application that reproduces the front panel of the HP6675A power supply. To achieve this, I have done a state machine with different states
(initialize, measures, voltage, current, ocp, ov, store, recall, etc). In each state, should have an event structure that catches the events of the buttons, like for example: if the current state is the Voltage mode and the user press the current button the next state will be the Current mode. For this in each state of the state machine should be the same event structure with the same events.
My problem is that the Vi doesn't work properly when I have multiple event structures with the same event cases. There are some possibily to do this, and how? Or is impossible to have multiple events? I have been reading some posts, but I don't find solutions.
Any help is appreciated.
Thank you very much.
Solved!
Go to Solution.

natasftw wrote:
Or as others mentioned, make two parallel loops. In one loop, have your state machine. In the other, have just the Event Handler. Pass the events from the handler to the state machine by way of queues.
A proper state machine will not need the second loop. The "Wait For Event" or "Idle" state (whatever you want to call it) is all you really need in order to catch the user button presses. The setup is almost there. Maybe add a shift register to keep track of which state to go to in the case of a timeout on the Event Structure.
There are only two ways to tell somebody thanks: Kudos and Marked Solutions
Unofficial Forum Rules and Guidelines

Transfering a case structure to event structure

Hi, I am trying to transfer case structures that are currently set up to a control that if on prompt the user where to save and then save all following files to that location till end of program and if off the do nothing. I would like to enable these to be switched on and off at any point and know to use an event structure. The problem is I am new to coding with an event structure and have been able to get the button to work but not continuously save. I attached a screen shot of the original case structure and was wondering if someone could show me how to change it to the event structure format with the same functionality. I'm getting a little lost and confused. Thanks!
Attachments:
alltruecases.jpg ‏534 KB

I can't attach the vi due to the size and I do not think a simplified piece of code is going to help. I did however go through and stitch two jpegs together of the main two sequences. hopefully this gives a better idea of what I am trying to do and where to go from here. thank you.
Attachments:
1.jpg ‏669 KB
2.jpg ‏317 KB

How do i get a boolean indicator to trigger a event structure

I have two parallel loops running, and i need to use a boolean value, one that comes out from an OR gate, to trigger an event in the parallel, event structure loop. I've attached a simplified version of the loop. Is there a way to get this done? I've tried using local variables, value(signaling), etc. and they haven't worked
Solved!
Go to Solution.
Attachments:
Parallel Loop Trigger.vi ‏10 KB

Here is a revised version of your VI. I modified the mechanical actino of the stop button so it kept it's value until it was read. In addition, I added a delay to your upper loop. Without a delay it was running too fast to actually see the button press. I modifed the event in the the event structure to trigger on a value change of Boolean.
You don't really need the outer loop since it will only run a single time in all instances. On the first execution of that loop it will be sitting in the turn inner loops. Once you exit the two inner loops your outer loop will always exit. Therefore, it serves no purpose.
Your OR in the upper loop is completely uses. It serves no purpose since the result will always be equal to the value of the Stop button.
There are better ways of triggering events. a preferred method would be to use a user event and simply generate the event at the appropriate time. This has the advantage of not requiring additional controls/indicators simply to cause an event to occur.
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
Attachments:
Parallel Loop Trigger.vi ‏12 KB

Event structure vs case structure?

I am developing an application that is fairly user input based... lots of boolean control buttons to do different things.
In the past, I have avoided "value change" event structures, and instead went with a while loop, stacked sequence, and series of case structures. After having done it, I decided this was a terrible idea. This time, I intend to build an array from the booleans, convert it to a number, and feed it in to a single case structure. This will give me the option to add cases for different combinations of the booleans being pressed.
I guess the question is: What is the best method for doing something like this? Does one have advantages over the other?
Edit: I wasn't that clear. I would like a comparison between the "value change" event structure method, and just feeding everything in to an array -> case structure. I also am worried that with the bool array -> case structure that I will run in to problems where I end up with too many control variables, and the value of the resulting number gets ugly very quickly. The application has several buttons... next, last, save, load, several different configure setup buttons etc.
Thanks!
Solved!
Go to Solution.

Aalenox wrote:
I am developing an application that is fairly user input based... lots of boolean control buttons to do different things.
In the past, I have avoided "value change" event structures, and instead went with a while loop, stacked sequence, and series of case structures. After having done it, I decided this was a terrible idea. This time, I intend to build an array from the booleans, convert it to a number, and feed it in to a single case structure. This will give me the option to add cases for different combinations of the booleans being pressed.
I guess the question is: What is the best method for doing something like this? Does one have advantages over the other?
Edit: I wasn't that clear. I would like a comparison between the "value change" event structure method, and just feeding everything in to an array -> case structure. I also am worried that with the bool array -> case structure that I will run in to problems where I end up with too many control variables, and the value of the resulting number gets ugly very quickly. The application has several buttons... next, last, save, load, several different configure setup buttons etc.
Thanks!
Event structure. Among other things, it will allow your loop to "sleep." then wake up when an event happens. With a case structure it's going to be constantly polling. Event structure is pretty much always the right way to go in newer versions of LabVIEW that have it available. I assure you, your first solution was aboslutely wrong and you noticed that, your second is better and was common the way before event structures existed, now that event structures exist, you should go with those.
CLA, LabVIEW Versions 2010-2013

Add event cases to an event structure using scripting

Hello,
Iam trying to (using scripting) update an event structure (add event cases) on a vi that is not on memory.
i get error 1054 The specified object was not found.
here is a picture of it.
any help in this will be greatly apreaciated.
Solved!
Go to Solution.

Another suggestion, the following VI is a wrapper for Traverse for GObjects VI and allows you to specify the name of the object you want. I always use this VI, I never use the Open VI Object Reference function, for the reasons tst mentioned:
vi.lib\Utility\traverseref.llb\TRef Find Object By Label.vi
Darren Nattinger, CLA
LabVIEW Artisan and Nugget Penman

Case order of EVENT structure

LV 8.2.1 - Regarding the order of cases in an EVENT structure:
1... Is there any performance (speed) advantage to having the most-commonly used events near the top of the list? Does it have to search through a list to find which case to execute, or does it happen some other way? If it searches thru a list, then I want to have the high-frequency events near the top of the list, and the rarer ones nearer the bottom.
2... If #1 is "no advantage" then what is the point of the REARRANGE CASES dialog? Why would I want to rearrange them? Maybe just to collect them into groups of similar function - is that all?
3... When you SORT CASES in the REARRANGE CASES dialog, what order does it put them in? The help window says "alphabetical" , but that's plainly not true, because my list includes "Stop" and "Clear", and it orders "Stop" before "Clear" after a sort. It doesn't put the user events together. A simple test shows that SORT puts them back in the order you added the cases to the structure. Is there a point to that?
Steve Bird
Culverson Software - Elegant software that is a pleasure to use.
Culverson.com
Blog for (mostly LabVIEW) programmers: Tips And Tricks

is it possible you have some invisible chars (like a leading space) or that one of the words starts with an uppercase letter and the other with a lowercase one?
Nope. Try it yourself with the Wed, Thur, Friday trick.
The EVENT structure cares about what order you created the cases in.
The CASE structure cares about the order of whatever drives the selector.
Alphabetic order seems to have nothing to do with it.
From your reference thread:
However, this does tell you that if you want to squeeze every ounce of performance out of your event-handling code, make sure the most frequently run event-handling diagram is the first one in the list.
This from a LabVIEW R&D engineer.
Hmmm.
Steve Bird
Culverson Software - Elegant software that is a pleasure to use.
Culverson.com
Blog for (mostly LabVIEW) programmers: Tips And Tricks

Trigger Event Structure Case on Startup

Similar Messages

Maybe you are looking for