Case Structures in LabVIEW 8.5

Is there any way to have a case structure based on different file paths? In the VI I'm creating, there are limited number of files that a user can read in and I want to have different cases depending on which file path they chose.
Hopefully this question is worded well enough for you to understand what I am asking for.
Thanks!

I am assuming that with "different file paths", you mean different files in the same location. Is this correct?
Let's assume that all the files are in the same location.
In this case you could also just strip the path and wire the filename to the case structure.
It is somewhat better self-documenting.
Message Edited by altenbach on 06-12-2008 12:56 PM
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Attachments:
fileCase.PNG ‏6 KB

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How do I get a case structure's panel?

I am trying to place a boolean indicator within a case structure via LabVIEW scripting and am not having any luck.
I started with the following source code, which creates and populates a case structure from an array:
https://decibel.ni.com/content/docs/DOC-22703
So my code, rather than put an enum inside each case, creates some compound arithmetic and a mask for each case. This is all working fine. I now want to place boolean indicators on the front panel that correspond to each case, and this is where my problem is. I can create the indicators, but when I look at the block diagram view, all of the indicators are located outside of the case structure, rather than the indicators being inside of each respective case.
I think the reason is that a boolean indicator is created by passing a reference to the front panel. But the problem with this is that the VI panel reference does not indicate that the boolean should be placed inside the case structure, just on the panel, so when you view in block diagram mode, it's just thrown the indicators all outside the case structure and wired them up via tunnels. I am getting the panel reference by accessing the OwningVI field of my CaseSel object. I feel like there must be some field I should be able to access that indicates to put the block-diagram boolean inside of the respective case structure, but I can't find it.
I've attached a file with 3 pics in it. One shows a pic of the code I'm using to create the indicators. One shows the type of output I'm looking for. One shows the type of output I'm getting.
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Attachments:
lv_case_struct.jpg ‏221 KB

Before you connect the wire to the terminal, call the Move method on the indicator's terminal and use one of the case structure's Diagrams[] as the owner. This will move the terminal into the structure.
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Disable labview changing a constant that was wired to a Case structure

Hi,
When upgrading from Labview 7.1 to 8.2 I get the following warning:
- LabVIEW 8.2 changed a constant that was wired to a Case structure to a hidden control to maintain compatibility with LabVIEW 7.1 and earlier.
I have read the post describing why this happens:
http://forums.ni.com/ni/board/message?board.id=170&message.id=258528&query.id=18820
Typically I have used a constant wired to case structures to comment out code, and therefore don't really care if the compiler doesn't load into memory.
Is there anyway to stop Labview 8.2 converting constants wired to case structures into hidden controls? E.g. As an import option?
Thanks in advance

I don't think there is a way to disable that upgrade feature, but it does not really matter, because the function remains the same. Just ignore the upgrade note.
To disable code, you should now use the "diagram disable structure". It has the big advantage over your solution that the disabled code can be broken and the VI is still runnable.
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Why does Labview insert quotations in the case structure selector box?

I was building a case structure with an array of strings. So, I copied the strings from the array on the FRONT PANEL directly into the SELECTOR LABEL. My 3 strings have the form; to me, these are 5- character strings with spaces, or 7 characters if you count the spaces as string characters
A, B, C
A, B, D
A, B, E
So, when I copied and pasted them directly into the selector box A, B, C appeared as "A", "B", "C" and A, B, D appeared as "A", "B", "C" and then I got an error for selector values not unique. Why didn't it appear as "A, B, C"?
Why did it transform the string I pasted and insert the quotation marks? I used no quotation marks in my array. Does the selector label interpret commas as functional characters that require quotation marks??
Thanks,
Dave

dav2010 wrote:
I was building a case structure with an array of strings. So, I copied the strings from the array on the FRONT PANEL directly into the SELECTOR LABEL. My 3 strings have the form; to me, these are 5- character strings with spaces, or 7 characters if you count the spaces as string characters
A, B, C
A, B, D
A, B, E
So, when I copied and pasted them directly into the selector box A, B, C appeared as "A", "B", "C" and A, B, D appeared as "A", "B", "C" and then I got an error for selector values not unique. Why didn't it appear as "A, B, C"?
Why did it transform the string I pasted and insert the quotation marks? I used no quotation marks in my array. Does the selector label interpret commas as functional characters that require quotation marks??
Thanks,
Dave
Actually in CASE STRUCTURE, any frame can have multiple values as 'Case Selector value' and these are separated by a comma. Also if you choose to operate a CASE STRUCTURE using string, it will automatically prefixs & suffixs quotes (") to that string.
But you can enter "A, B, C" manually and it will remain as it is. But if you copy and paste A, B, C, the CASE STRUCTURE will automatically change it to "A", "B", "C".
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Passing data in case structures Labview 6.1

I have a simple case structure consisting of 4 frames inside a while loop. I want to pass data from the 3 cases thru the while loop and display on indicators.
After running the vi only data from the last case is displayed on the indicator.
How do I pass data from each case to the indicators?
Attache dis the simple vi to show the problem.

Using Local Variables is almost never the way to go. Sometimes they can't be avoided, but most of the time there's another way.
I've modified your example a bit. The new loop below your original one will do the same thing, but without using variables. The For loop automatically indexes through the array and will process each element. The Shift Registers pass data from iteration of the loop of the next, so the values from the first iterations will stay around so they can passed out of the loop.
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Attachments:
LoopTest1_using_For_Loop.vi ‏58 KB

Can I put a READ function in a TRUE/FALSE case structure?

Hi,
I have a vi that operates as controller for a mechanical system of motors. There are several sensors of various types, that provide input to the vi, including encoders, whose period is being measured. The attached vi is the encoder period measuring part. It measures 15 periods and tells me the average of the 15 with each loop iteration.
In my application, the encoder period measurement is not needed unless the vi knows that ALL THE OTHER sensors in the hardware configuration are measuring values within the desired range. For example, Sensors A, B and C should all measure between 5-10. If they are all showing values between 5-10, then, we want the encoder value to read and display. If only one of the sensors, say A, is measuring 12, then, we don't want the period value to READ or be subsequently processed. So, it is easy to set up the sensors A, B, C, to give a TRUE or FALSE based on whether they are within range or not, and if all 3 are TRUE, then, that value can easily be passed to the case structure that holds my READ function for the period. Is this a good way to do this? The goal is to eliminate unnecessary execution time that the period READ function would consume, as well as all subsequent calculations that are performed on the period value collected. The period data is of no use if any one of the other sensors is not in the correct range.
If any one of the other sensors is out of range, we want to skip the encoder READ step altogether. So, it is easy to structure a BOOLEAN in my vi as shown in the attachment. If I do it this way, will it throw an error, or just skip the READ until the BOOLEAN is true again? Is there a better way to prevent the READ from happening if one of my other sensor values is not within the correct range?
Thanks,
Dave
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Attachments:
forum JUly 18.vi ‏26 KB

Sure, you can put a Read inside a case structure. For your application, just check that your sensors are all within range (Comparisons palette), then AND the T/F's and use the result of that for your case structure. (If you are already doing the in-range check, I can't see it here because you have 5 subVIs that I cannot open here.
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Run only once in case structure

Hello,
I have a menu set up that is wired to a case structure. Of course the menu is some boolean buttons that are set to switch when pressed so the case will stay open as long as the button is true.
inside that case I have another menu and a case structure that operates the same. In one of these cases I have a piece of code that I only want to run once. I have tried the while loop that runs once and a for loop that only runs once, but the section of code seems to run continuosly instead of just once. It works ok if I use any of the latch functions but not the switch when pressed functions. However, I need the button to stay pressed until the user is finished with that case.
I really don't want to use an event structure as I was saving that for another piece of code that monitors inputs.
Anyone have a suggestion?

Typically, this works easiest with a shift register and and a boolean "implies" function.
In the code example (see image), the button is set to "switch until released". (Of course you probably don't need the NOT, simply place your one-time code into the FALSE case )
Message Edited by altenbach on 01-26-2007 01:52 PM
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Attachments:
implies.png ‏8 KB

Problem with multiple sub-panels through Enum case structure: "The VI is not in a state compatible with this operation"

Hello,
I am using LabVIEW 8.0 and I am attempting to create a sub-panel that displays the front panel of a sub-vi depending on the selection made by the user via the Enum dropdown menu. I have wired the Enum to a case structure and applied identical coding to each individual case structure except for obviously changing the sub-vi source. However, I receive an error "The VI is not in a state compatible with this operation." I was able to successfully make a single sub-vi work within a sub-panel using a true/false case structure and the exact same coding. However, now that I am using an Enum box wired to a case structure, I receive this error. I have attached my block diagram as well. Could anyone assist me as to where it is that I am going wrong?
Thanks in advance!
Solved!
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Attachments:
enum subpanels.JPG ‏22 KB

torm wrote:
I have attached my block diagram as well
I only see a picture. Can you attach the VI instead? At what point do you close the reference?
torm wrote:
I have wired the Enum to a case structure and applied identical coding to each individual case structure except for obviously changing the sub-vi source.
Well, if the code is identical except for the source, only the source should be inside the case, right? Why duplicate code?
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The case structure is not working well on comaring two strings using true or false string matching VI

I need an execution of commands after the reply from the instrument matches with the string I provided for that i used true or false string match VI on which the true string the matching command and the string is the reply from the instrument. And I put the further executionable commands in frame after frame of sequence loop in the true of the case structure. Amd finally I given all the output strings to the concatenate string to get all the replies as one loop. But when I execute the program the desired result is not available. So kindly please help me to overcome this problem.
Attachments:
basic serial with changes.vi ‏24 KB

You VI makes absolutely no sense and I would recommend you start with a few simple LabVIEW tutorials before trying to tackle this.
What is the point of the FOR loop with 1 iteration, it might as well not even be there, same difference.
Why is there an abort primitive in the FOR loop, this mean the program will unconditionally stop abort before any downstream code will ever go into action. The program will never get past the FOR loop.
You created a circular data dependency and LabVIEW inserted a feedback node automatically, making things even worse. (see also)
You need to learn about dataflow, execution order, and data dependency.
You need to learn about the various types of tunnels (plain, autoindexing, etc.)
There is a tremendous amount of duplicate code. Large code sections are the same, differeing only by a string. You should only have one copy of that code inside a proper state machine. Have a look at the design templates and examples that ship with LabVIEW.
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I want to create an array that goes into a case structure where each element in the array is an individual case and gets done in order

I want to create an array that goes into a case structure where each element in the array is an individual case and gets done in order. Any ideas, I've been playing with the idea but have had no luck, is this even possible?

Hi,
Please check it out the attached Vi.. Is this you need?
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Attachments:
Event.vi ‏11 KB

Case structure with more than 200 cases, slower lab view app

Problem Description :
i am currently making a vi which compose of a simple case structures, a case structure with more than 200 cases, what i noticed is that the more i added cases the slower the labview reacts, it takes time for me to route wire on each of the cases.
i dont know if there are any setting in the labview environment that i can increase the buffer size? i dont know... but its getting slow (only on the
vi with more cases in a case structure)
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Can you clarify what you mean by "slow". Does it run more slowly or does it feel sluggish during editing?
Could you attach the actual VI?
Overall, I agree with the notion of local variable overuse. For example, you read the same local variable twice in the same case. Is there a need for this? Is there a chance that it varies between the two reads? Typically, you would place the terminal in front of the case structure and wire to all the locations where you need the value. This ensures that the data is consistent. Still, this should not cause any slowdown problem.
(On a sidenote, the code in the upper left corner is inefficient. You convert the same data to lower case with each iteration, so you might want to place this before the loop and do it only once (well, if you are lucky, LabVIEW will fold the operation, but still....). Also your "index array" operation can be replaced by autoidenxing of the 2D array on the outer loop boundary.)
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Multiple booleans controlling one boolean input for a case structure

Hello,
I have four boolean buttons and a case structure with a boolean input. I would like to write the program so that whenever any one of the four boolean button changes value, the case structure reads true for one loop interation, and then returns to false.
I have tried all sorts of things and can't seem to figure it out.
Ultimately, the ideal function of the program is so that whenever you push any one of the four boolean voltage controllers, that voltage case is chosen in the case structure, the time in seconds is written to a file, and the elapsed time timer is reset.
I have attached my program. Let me know if you have suggestions. Thanks.
Attachments:
Volt_Control_And_Time_Counter.vi ‏71 KB

Zappow wrote:
However, with this setup, the time counter still doesn't work.
The event structure for all four buttons has a true boolean constant connected to my file-saving case structure. If I connect this to my elapsed time express VI reset button, the timer doesn't count.
The timer does not count because you have not wired a timeout to the lower event structure. The default timeout is -1, so the lower loop never spins via timeout
It is useless to have a wait in a loop that also has a timeout case. Just wire an approriate timeout value to the timeout terminal and remove all waits. It is also not necessary to have a 1ms ttimeout if your timeout values only displays to 100ms resolution. Can you explain why you think you need two loops and all that extra code?
Attached is a quick rewrite that solves some of the problem. Since I don't have any hardware, I replace the voltage out with a meter.
You have way too many FP controls and indicators. Use arrays!
Let me know if yo have any questions. Modify as needed.
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Attachments:
Volt_Control_And_Time_CounterMOD.vi ‏63 KB

Why won't my charts continually update while running a case structure?

I'm making a VI to drive an actuator and read a force on a load cell. I have programmed the actuator to run through a flat sequence using millisecond timers to delay its drives outward and inward, which is necessary for its intended use. However, my goal is to have it display the motor position and the force on the load cell on the charts continuously throughout the test. However, when activating the case structure containing the test sequence, the graph fails to update live.
I'm not sure if I'm on the right track, but I have posed my file for whomever is interested. I hope you can lead me in the right direction, and thank you very much.
Keith Blume
Attachments:
Final VI.vi ‏303 KB

johnsold wrote:
You can find the version of a VI you have downloaded (as long as you have not saved it) by closing the window.
Well, closing the window is a bit drastic.
Simply go to VI-properties (e.g. by right-clicking the icon in the upper right) and do: "General...list unsaved changes"
Message Edited by altenbach on 12-16-2008 08:53 AM
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Attachments:
Version.png ‏31 KB

Trying to clear an array inside a case structure

Good morning all. I am trying (unsuccessfully, obviously) to clear an array inside a case structure. (See case structure at right side of vi, I colored it green to make it easy to find). Here's (briefly) what I'm trying to do. I have 6 test probes in the process. All six probes are connected to the Alcatel Detector through a 6-solenoid manifold. As I run the test, I want to sample 1/second, for let's say 3 minutes. For the first 30 seconds, I want to pull a sample from from probe 1, so I turn on solenoid one and leave it open for 30 seconds. Now all 30 values are tagged as having come from Probe 1, and they're stored in array 1. I can now compute an average value for probe 1. Then I close solenoid 1 and open solenoid 2, saving the next 30 values to array 2. (and so-on, until I have measured all 6 probes for 30 seconds each). Then I wait a pre-determined amount of time and repeat the process. Here's my problem. I want to clear out each array as I begin the second iteration, so that I can easily compute the average of the last 30 values. If I initialize the array by connecting a constant 0 to the shift register on the for loop insid ethe case structure, it does not work, nor does it work to place the 0 outide the overall for loop (the next for loop going out, NOT the OVERALL for loop). I know my programming skills are still crude, but I'm putting everything into this. Anyone have any suggestions?
Attachments:
HCMF rev 1 25 Apr.vi ‏485 KB

Altenbach, I definately understand your approach, and I like it much better than my own. But I still have no luck making it work. I get the same result as before (my original attempt). Value 0 of the array simply changes each iteration, with nothing "saved". Each new value simply overwrites the last value. Can you take a look at my new vi, with changes, and see if you can find the error of my ways. I am but a rookie Jedi in the vast reaches of LabVIEW Space, and you are no doubt a Jedi MASTER
Attachments:
HCMF rev 1 25 Apr pm.vi ‏374 KB

Range setting in case structure

Hello everyone! I'm working on an engineering project where I read in a sound input and if it's on high volume, a red led connected to a MyDaq box lights up, if it's on low, the green LED lights up, and both will be off if there's no sound input. I posted a screenshot of how my vi currently looks. The problem I'm having is, I want to set the range that will be considered as the low volume, and a range considered as the high volume on my case structures. I'm not sure exactly how to do that. I currently have an "In range" function there where I set the max and min values. THe problem with this is, it outputs a dynamic data that I cannot connect to the appended array. Any help would be great. Thanks!
Attachments:
projecttest2.vi ‏91 KB

Thanks for your response. I'm new to labview (which isn't really an excuse) and we just went through the real basic stuff for this course. That's why my code just looks like a mess. I'm just trying to use the case selector because I thought it'd be more efficient, since, if I think of it in written code, they're kind of like if-else statements, right? I thought I needed to multiply by a thousand because I am measuring the amplitude of sound input. Whenever I test it out, the numbers are really small. I just figured it'd be easier to multiply it by a thousand and set the range with bigger numbers. I'm also trying to get an LED to light up on a range of volume. That's why I need two comparisons. Like, if the volume is between the range of 2000 to 3000, the green LED lights up, and if it's between 1000 to 2000, then the red LED lights up. If the signal is equal to zero, then no light turns on. Anyway, I scrapped the whole idea of using case selectors because I don't have time to learn my way through it and finish on time. I attached a new version of my VI. It's a more simplified version. I don't know how to connect the LED boolean indicators into my array and into the DAQ Assistant (it's not on the vi yet but I do need one so the program knows to read the output into the LED's on my myDaq box. Sorry for the trouble! Thanks for any advice you can give.
Attachments:
projecttest1.vi ‏55 KB

Case Structures in LabVIEW 8.5

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