Control buttons in local variables

hi,
i have been trying to do this for a long time. i just never learned how to make it work. can someone please guide me?
i have this program with many many local variables and i know that this forum absolutely hate LOCAL VARIABLES.
I want to program this the right way, so can you guys please help take a look at my code and see what i can do in order to REMOVE local variables if possible?
Best regards,
Krispiekream
Attachments:
test.vi ‏768 KB

does this work?
i split up the zip file to 2.88mb each.
i think there is a file size limit of 5mb
can you rename test01.zip to test.z01
can you rename test02.zip to test.z02
Best regards,
Krispiekream
Attachments:
test.zip ‏1078 KB
test01.zip ‏2847 KB
test02.zip ‏2847 KB

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Local variable event structure

Hi,
I am using an array control and event structure for detecting changes in the array value.
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How can you create a local variable from a boolean control?

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> I want to create a local variable from a boolean control, but it says
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A little backstory which I should have given when I asked the question.
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Problem using local variable in event loop

I have a state machine from which I want to monitor various controls, including "Start" and "Stop" buttons. Not every state needs to monitor the controls. At present, most states run timed loops. In the first state that reads the front panel, I have an Event structure (inside a While loop) that monitors the various controls' Change Value events. For numeric controls, I update variables (in shift registers) as needed. The "Start" button is used to end the While loop controlling the Event structure, allowing the State to exit to the next state.
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Attachments:
Simple Stop Conundrum.vi ‏14 KB

altenbach wrote:
Ravens Fan wrote:
NEVER have multiple event structures that share the same events.
Actually, that's OK. NOT OK is having multiple event structures in the same sequence structure.
See also: http://forums.ni.com/ni/board/message?board.id=170&message.id=278981#M278981
That's interesting. I had always thought I read more messages discouraging such a thing rather than saying it was okay. Your link lead me to another thread with this message. http://forums.ni.com/ni/board/message?board.id=170&message.id=245793#M245793. Now that thread was mainly concentrating on registered user events which would be a different, but related animal.
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Variation between local variables

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1. Your VI is designed to only run one time. It runs once. Then it stops. My guess is your are using the Run Continuously button. Don't. It is only intended for special situations like if you want to debug a VI. If you want your VI to keep running, then use a while loop around it and a stop button.
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To make things clear, here are two small examples that show how nasty locals and value properties can be to the naive programmer.
- Open the diagram of the race condition.vi before running it and try to predict what will be the values of the two counters after the third run.
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Race condition.vi ‏9 KB
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Data Acquisition - using local variables to write data to a file

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Hi jilla,
jilla wrote:
What I think that you are saying is to turn the outputs of the 4 subVIs into inputs of a 5th subVI that writes to the data file. Correct?
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One more question: at what point (either # of data points or frequency of data collection) does it become necessary to use queues? Thanks.
Well, there's not really a clearly definable "point". I'd say if your update-rate climbs above 100Hz, or you witness poor program or system performance, then it's time. The scenario you've described is a fairly simple acquire/display&log loop - and simple is good. Then-again people can't see/react-to updates faster than about 10Hz - so it doesn't make sense to sacrifice performance - if performance becomes an issue.
Re: queues: Queues are sometimes used to buffer data that's "produced" in one place and "consumed" in another.
Here, if/when logging data, you're logging with every DAQ. I wouldn't recommend using a queue to transport data from a "DAQ loop" to a "Logging-loop" - those functions can be in the same loop. Should/could a queue be used to get data from a "DAQ loop" to update the GUI at a lower frequency? Sure, but a Notifier might be a better choice. Further, in the (simple?) program you've described, you might use a case structure (True/False) to only update FP indicators every "X" iterations - a simple solution that doesn't require Queues or Notifiers.
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How can I put the contents of an array into a set of write local variable clusters?

I have a set of controls that a user fills in. The controls are clustered by rows, then combined into a 1D array, then written to a file. When I read the file, I want to feed the array back into the clusters with write local variables. Is there a simple way to handle the numerous local variable clusters so I can stuff the array back into them?
Is there a better way to handle the whole issue of storing and recovering the information?
The rows are steps in a procedure, and each row (cluster) contains numerical as well as string controls.

There are many ways of doing this
You may convert all your data to strings and save as an ascii file (you have to pay attention to the file format, so you can read it properly.
Or you can use the configuration vi's, it may work in your case.
or you may use an invoke node to get all controls of the vi's, save it, then read it, without worrying about any format. I have attached a vi that uses this method.
Attachments:
Temp.vi ‏52 KB

Does a large amount of "local variable" within a vi cause problems?

Hello -- I am using Labview 7.0 and have a vi where I am going to end up using about 100 "local variables" for indicators that are displaying data. Since I have a lot of true / false case structures I decided to use these local variables instead of having a mess of wiring all over the vi block diagram. It is intimidating though and I was wondering if it causes slowness in vi's?

I actually only have about 8 indicators -- but I am in the process of creating control algorithms so I have to use many case structures if I want to keep the code all within Labview (simplicity). I am simply referencing the 8 or so indicator values many many times (100 X) I am attaching a copy of the vi like you asked but just take a look at the right hand side of the while loop on the right -- it shows an example of an algorithm I created today that has to reference the data from sensors. I would love to know what a better way to do this. Thanks!
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How many ways to read and write a local variable in a called VI?

Ciao!
I'm producing my first TestStand sequence. It is called "FirstAttempt" and it is made by a single step which calls a VI. One of the first dilemmas i encountered realizing this sequence is how to read and write a local variable (created going in Variables -> Locals ('FirstAttempt') -> <right click to insert local>) in the called VI.
The first way (the only one i tried) is to create a control and an indicator on the VI front panel, connect them to their respective terminals in the connector pane and then specify (going in Step Settings -> Module) that these connectors (shown in the Parameter Name column) are linked to the local variable (selected in the Value column).
The second way (not tried) consists in using TestStand API: create a Sequence Context reference on the VI front panel, link it to a property node in the block diagram, select the property "Locals" and extract from this the local variable name and value which, i think, can be readable and writable.
So...
Are the shown ways correct?
Are there other ways?
Knowing that a "local" variable can be considered "global" within the whole sequence, is there the possibility to simply create a reference to the local variable and use the reference in the called VI block diagram in order to save space in the connector pane (if using method 1) or in the block diagram (if using method 2)?
Thanks!
Message Edited by aRCo on 09-17-2009 05:09 AM

Hi,
Before TestStand 3 you would use the second way you quoted as its the only way.
But now you would use the first way you quoted. You may still what to pass the SequenceContext if you were going to use the TestStand API. For TestStand 3.x and above you would use this way as the first chose. (Personnelly, I would not pass the SequenceContext into a VI if I know it was never going to be used in that VI.)
Not sure I understand your final comment, maybe you are liking it to passing the reference of a control to a subVI so that the control can be updated from within the subVI.
If this is the case and you had a situation where you had a step that was running in parallel with the rest of the steps in the sequence either as a separate thread or execution and were dependent on the contents of the local variable changing from that parallel running step, then you would have to use the API SetVal method to change the local.
Hope this is clear.
Regards
Ray Farmer
Regards
Ray Farmer

RE: local variable cross-talk?

Jeff
A global can be considered as a variable to the entire code, where lots of
different vi's can operate it. Locals only have any meaning within their
own vi, or instances of their own vi.
If anything writes to a particular global, whether in reenterent vi's or
not, it's available everywhere in the code.
What you were asking was about locals though. If a vi is non-renentrant
(i.e. as they come out of the box) then the values in the locals are vi
specific, no matter where the vi is, where it was last used, it retains the
data from it's last operation. If it is re-entrant, then the values in the
locals for each occurance of the vi are its own for EACH instance, i.e. just
like different locals in different vi's, it doesn't matter where else the vi
is used, the data held is that from the last operation of that specific
instance.
Simple way to demonstrate this. Make a vi that has one numeric control,
then code in +1 and get it to write to a local variable for that control.
Throw in an indicator to wire out the result of what is written to the local
for the control.
Then take this vi, put it in a for loop, then put another copy in the for
loop as well. Wire the indicators to the side of the for loop and create
indicator arrays for them. Get the loop to run 6 times say. Now try
running this with the vi in the for loop non-reentrant and then reenterrant.
One way the arrays will contain either all the odd no.s 1,3,5,7,9,11 and
then the other array 2,4,6,8,10,12 (don't know which array will be which,
depends which executes first in the for loop of this example). The other
way they will both be 1,2,3,4,5,6. In the first example, the same vi has
run 12 times, i.e. one copy of the vi which retains its info and is called
in many places and therefore only has one set of values, and the other with
two re-enterant copies where they have their information specific to that
instance of them i.e. effectively they are different vi's. Both ways are
useful, depends what you want.
If you're looking for a use for non-reenterant vi's then consider this:-
For instance. Supposing you get many things to try to write to a global
array of numbers, and you have two vi's one "A" writes to the first element
in the array and the other "B" writes to the second element. Because in LV
you have to read a global first and then write to it to perform a change,
these independant vi's "A" and "B" (be they re-enterant versions of the same
vi, or different vi's), can be performing the tasks simultaneously in the
code. I.e. "A" reads, "B" reads, "A" writes, and "B" writes over the top
with a modified version of what it read, and "A"'s changes are lost. This
is what's known as a "race condition" as "A" hadn't finished and "B" needed
to know what "A" was going to write before "B" performed "A" read. Try it,
hours of fun if you code this kind of thing in inadvertantly!
If the same vi is used, and is not re enterant, it can only run in one
instance at a time, hence two read / write operations cannot be performed
together, problem solved. Unless that gives you timing issues of course,
waiting for one to finish, to write the other......but that's another whole
can of worms.
cheers
Tim Price
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-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Jeffrey W Percival
Sent: 29 November 2001 21:12
To: [email protected]
Subject: Re: local variable cross-talk?
Another useful reply! What a great news group this is.
One last thing I wanted to ask about, though, is global vs. local. I see
you talk about globals, but in fact the variables in my subVI's were locals.
I can easily understand the behavior I observed accompanying the use of
global variables, But I guess the use of the word "local" stumped me.
Should I interpret "local" in LabVIEW's sense to mean "local to all
instances of this VI"? And global to mean "visible to all instances of this
VI as well as other VI's"?
-Jeff
Tim Price wrote:
This facility is actually very useful, for instances where you want to
encapsulate some code so that it can only run in one place at a time,
i.e.
global arrays that are written to in more than one place. This method
can
eradicate race conditions completely for example when used like this.
There
are multiple other uses as well.
However, using a vi as a module of code, to run in more than one
instance at
a time simultaneously, re-entrant is the way to go. Just make sure you
debug it first!!!
Remember though, just because a vi may be re-eneterant, doesn't mean
that
everything inside is; sub-vi's, Globals etc. The classic one I've seen
is
where people think that a re-enterant vi is talking to it's own copy of
any
Globals used within it, i.e. counters etc., where in actual fact of
course,
they are all using the same Globals.
Worth playing with a few examples to get familiar with it.
Tim Price
Jeffrey W Percival, Senior Scientist and Associate Director
Space Astronomy Laboratory, University of Wisconsin - Madison
1150 University Ave, Madison, WI 53706 USA
608-262-8686 (fax 608-263-0361) [email protected]
http://www.sal.wisc.edu/~jwp

Tim Price wrote:
Tim, thanks very much. I'll try the experiment you suggest.
Thanks for taking the time.
-Jeff
Jeffrey W Percival, Senior Scientist and Associate Director
Space Astronomy Laboratory, University of Wisconsin - Madison
1150 University Ave, Madison, WI 53706 USA
608-262-8686 (fax 608-263-0361) [email protected] http://www.sal.wisc.edu/~jwp

Sampling local variable and synchronize with DAQmx

Hello,
I made a small change in the set-up I used with labview and now when I wanted to change the code I'm having a rather complicated problem.
In my old set-up I was measuring three variables: x and y with a QPD and the power of a laser with a power detector. I was using the DAQmx and I was getting a matrix with three columns with n (sample rate) values. Now, for various reasons I had to take out the second detector. So now I want to build the same matrix as constructed before, but instead of putting the measured values of the laser power I want to put the theoretical values (they are in a local variable) as I cannot measure them. The problem is that this local variable, in general, changes during the DAQmx acquisition time and I would need to sample it at the same rate as I acquire the data from DAQ and then combine all them. How I could sample this variable and attach it to my DAQ results? DAQmx doesn't accept local variables.
Thanks

A local variable is not something standalone. It is always associated with a control or indicator. Hows is it updated?
From your description, it is not clear what you are doing. Can you show us some code instead?
(Also be more clear when using acronyms. QPD cound mean many things)
LabVIEW Champion . Do more with less code and in less time .

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