Repeating case structure

This program is supposed to recognize an input voltage of 5V and then proceed to start the vertical bar picture box moving either left or right, per the users choice. The user can also input the desired bar width, scroll speed, and cycle duration (time to get from left to right and back). I want the picture box to move left and right repeately. On frame #3 of the stacked sequence I have made a case stucture that would play the true program if the iteration for the larger for loop is even (or zero) and false if odd. When run, the program will only move left first then right and then stop completely. How do I get the case structure to consistently repeat between alternating the false and true cases?
Thank you!!
Attachments:
vert rect with volt data.vi ‏1387 KB

Chip,
Please consider rethinking your code from scratch, the code is virtually unmanageable and full of race conditions due to overuse of local variables. It will never work as desired in its current form.
You might also read my comment here: http://forums.ni.com/ni/board/message?board.id=170&message.id=112401&query.id=0#M112401
Unecessary code: Once you create the image in frame 0, its content never changes. There is no need to carry the wire and rewrite the same data to a local variable of the image in subsequent frames.
I would suggest NOT to use formula express VIs for simple operations sich as "divide by two", "2*x1*x2", etc. Since the formula is hidden it is impossible to see what is going on without clicking the express VI. Use plain wires and basic math nodes!
Don't use value property nodes if the actual wire is right there. Just use a plain wire, eliminating the property node (property nodes pose a sever performance penalty).
It is also very confusing to have multiple terminals with the same name (e.g. "Trial Duration (s)", etc.). You have four (!) instances of basically the same while loop, where the only difference is one diagram constant. They can all be combined into one and have the diagram constant be a function of the current "state".
Race Conditions!!!
As an example, lets have a look at your first FOR loop. Since several code elements are chopped up without any direct data dependency, there is no way to tell what occurs first. (LAbVIEW does NOT execute left to right!). For example, you cannot tell if "Number of Bars Drawn" (A) gets written first or one or two of its two locals (B,C) get read first. Similarly, you cannot tell if D and E get updated before F and G get read. In a typical iteration, you'll probably get a random mix of stale and current values. There is no way to predict it.
The insert shows an alternative implementation. Dataflow exactly determines the sequence of events and no race condition can occur.
I am sure with very little work your code could be simplified to 10% of its current complexity. At this point we can start troubleshooting the problem you mentioned. Most likely, everything will fall into place.
Message Edited by altenbach on 06-28-2006 01:09 PM
LabVIEW Champion . Do more with less code and in less time .
Attachments:
VertRectWidth.png ‏32 KB

Similar Messages

Can I use a formula node to start the execution of a case structure?

Hi,
I am working on editing a VI to make it much easier to understand (for colleagues and non LV users). For one reason or another, the VI's creators did not fully make use of the power of case structures and other structure types. In the application we need it for, the instrument cycles and repeats measurements on several objects. We are interested in measuring the motor currents for several motors in the system. As it stands now, for each sample object's run, there is a separate sub-vi diagram which displays its waveform trace and several indicators such as max current, time at max, etc. That code was contained within a T/F case structure and copied and pasted 20 plus times.... Obviously the vi became extrememly cluttered and needed a huge screen to see. The trigger for the current case structures is an EQUALS comparison between one input (which is the sample object counter; and this part I will likely leave unchanged since it makes a lot of sense already) and a constant which was defined 1 through 20+ for case.
I have since made one case structure and 20+ instances of that case and have labeled them (at the top selection box near the detent arrows) "1", "2", 3, etc. I am wondering if I can use a formula node to act as the "trigger" which sets each case structure running? I believe that a simple IF statement should work. Please see a snippet of my attempt at making this in C below.
For the node, I defined X as the input and Y as the output. The input to the node, X, is connected to the sample object counter. The output, Y, is connected to the case selector of the case structure. My attempt at the code is below:
int32 y
For(x == 1)
y = "1";
For(x == 2)
y = "2";
etc, etc.
Is that above code snippet correct? Do i need something like "ENDIF" or "end if" at the end? Does "y" have to be defined as "int32" or can it be something else?
Thanks for the help!

Is your formula node doing anything else besides what is shown?
Why don't you just wire the value that is going into it at X directly into the selector of the case structure?
Attachments:
Example_VI_BD.png ‏2 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

Calculate maximum value of subarray while creating it using a case structure and shift registers

I have two 1D arrays that contain cyclical information (kind of like a sine wave). One that contains information on position in degrees and another that contains torque. I would like to calculate the maximum torque value each time the position is within a certain range (e.g. from 30-80 degrees). The ranges are repeated - that's why it is cyclical. I use the "in range" function, a case structure and shift registers to build a new array with values that fall within the range I specify - this was the easy part (see VI attached). I'm struggling with a way to calculate a maximum value for each subarray formed when values are "in range". Your help is much appreciated.
Solved!
Go to Solution.
Attachments:
Simple Calculate between anatomical position range.vi ‏16 KB

It's not really noise - it's more inconsistency. So a position output can run: 20, 30, 40, 50, 60 etc. OR, it could run: 21, 24, 32, 41, 44, 51, 59 etc. But, it is always cyclical.
Attached you will find a .csv file with the data arrays - I'm using POS (ANAT) degrees column (column D if you open in excel). There you also see torque in ft-lbs along with some other information.
Attachments:
025C.csv ‏224 KB

Can a case structure execute multiple cases?

So I have a VI set up with a mutiple option case structure to select which input a voltage is read from (there are 32 options). Now that I have it made, I realize that sometimes I may want to read from multiple inputs at once.. Is there an easy way to change my setup so that it executes multiple cases at a time? Right now my control is a slider to choose the case. What would be a good front panel control choice to be able to select multiple options? Thanks
Solved!
Go to Solution.

You can build an array of your options and loop through the required cases. As mentioned, a case can only perform 1 case per loop.
A good front panel control would be a cluster or an array of booleans (e.g. a tick box per option), easy to loop through.
/Y
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Case Structure Nested in a For Loop

I have two pumps. I want one pump to be running and the other pump to be off. Then as soon as the first pump stops I want the other pump to start. I'd like this process to repeat as many times as I want. The code I have now uses a case structure inside a for loop. When the iteration is odd it is false and even is true this determines what case is carried out. Right now I have a code that can turn on one pump, stop it, and immediately start the second. However, after the second pump stops the first one does not start again. I've changed the number of iterations and I can't seem to get the process to continue. The program keeps running but the pumps stop doing anything. Attached is a file of my code as well as two image files (one showing true case and other showing false) of the same code.
Attachments:
Test Code 1.vi ‏31 KB
Case if True.png ‏37 KB
Case if False.png ‏35 KB

Your code has an inner while loop that checks for the status of the pump. Since you set up a target volume before the while loops start, I assume that it is what the status checks to determine when to stop the while loop.
When the the second iteration ends, has the volume for the first pump changed at all? If it is still the same, then the status is still at the target which means it will immediately stop after starting. You may also want to put some small wait statements inside the inner while loops so that the status isn't checked as fast as the CPU will allow it to run eating up CPU cycles.

Programmatically change case structure range

I think I already know the answer to this, but I'm going to ask anyway. In the attached image, is it possible to programmatically change the range of numbers the case uses?
Tay
Solved!
Go to Solution.
Attachments:
case structure.png ‏3 KB

To use a property node on a case selector, you need to have a reference to it. There are several ways to open the reference, depending on where the object you want to reference is located.
EASY - If the case selector is not inside another structure and has a unique name, use Open VI Object Reference with the name of the case selector as the input. The owner is the block diagram reference and the object class is a case selector.
FAIRLY EASY - If the case selector is inside another structure or structures and all structures and the case selector have names unique to their diagrams, open the structures from outside to inside as in case 1. After you open the structure reference, get a reference to the appropriate diagram and repeat until you get to the final case selector.
HARDER - Case selector has a unique name, but is buried in a container which does not. Use the Traverse method to find all case selectors, then use the Label property of each to find the right one.
HARDEST - Case selector does not have a unique name. Use the Traverse method to find all case selectors, then find the one you want by the frame labels.
The take-home message from this is that your life is much easier if you give your containers unique names.
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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
Solved!
Go to Solution.
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.
Cameron
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How do I use a Case Structure with Strings?

I need to use a string list to set up a set of cases to be performed. Is it possible to tell a single case structure to do "a, b, c, and d, but not e or f" or "do a, c, d, and f, but not b or e" etc... when you use a string containing the cases to be used?

Blackavar,
A case structure will only execute a single case at a time. If you want to have multiple cases execute in parallel, then you would need to have multiple copies of the case structure and split the string apart and wire them to all of the needed case structures.
This could be done with reentrant subVIs to run truely in parallel. Anther method would be to have 6 different case structures, all with 7 cases each. The 7 cases would be "a", "b", "c", "d", "e", "f", and "0". Your input sting will need to be built up so that it will always be 6 characters long and then split up so that each character goes to one of the case structures. You would have your needed code for cases a - f. Case "0" would do nothing.
Randy Hos
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Applications Engineer
Nationsl Instruments
http://www.ni.com/ask

How can I pass data generated in a SubVI inside a Case Structure out of the Case Structure?

Hello,
I am using a USB 2701 to control a heater. I have three SubVIs that are all working properly on their own. I'd like to use an Enum to select which of the SubVIs is running at a given time. The problem is that no data is passing out of the case structure. How can I pass the temperatures and heater outputs acquired by the SubVIs to the main VI? I've attached my some of my code below. I can't attach more than 3 files, but you can see how the main VI is configured. Like I said, the SubVIs are working individually, so you shouldn't really need to look at them.
Thank you,
CJones581
Attachments:
RampHeater6-21-07.vi ‏305 KB
69_Heater_Case.vi ‏23 KB
HeaterTCD6-21-07.vi ‏210 KB

CJones,
You might check a couple of things.
Your HeaterTCD... VI has a While loop with a stop button condition. HeaterTCD pass out values only when it finishes running. If it doesn't pop open the front panel (which usually doesn't happen when running a SubVI) you could run into a stuck loop because you don't have access to the Stop button. This could appear in the form of no data being passed out (because the SubVI never stops running). The primary VI opens the HeaterTCD VI, starts it, and waits for the VI to finish and pass final values .
Secondary note: Unless you want your SubVI panel (which probably isn't open when running the main VI) to update continuously, consider moving your Temperature Graph and Temperature oC indicators outside the while loop. Pass final values to them via a tunnel, since the main VI will only read their values after the loop finishes running, anyway.
It might help to add error management to HeaterTCD like you have for RampHeater. If you connect error lines with Error Outs to your main VI, that will help tell if there is an error somewhere that is preventing info output.
RampHeater SubVI has the same issue with the stop button. It is also probably getting stuck in the While loop waiting for a manual push of that SubVI's Stop button.
An easy way to test this would be to set up a logic circuit so that when the While loop iteration counter reaches a certain number, it registers True and sends it to the conditional. I know this isn't what you want to do long-term, but if that lets your SubVI return outputs it means that the SubVI was just never stopping.
Hope that helps.
David C, Applications Engineering
David C
Applications Engineering

How can I have multiple inputs into the selector terminal of a case structure

Hi everyone
I have a question on how to wire multiple inputs in to the selector terminal of a case structure.
Currently, I have three switches, each switch determines different case. So if I switch the switch 1 is on, the numeric indicator will show 1. If the switch 2 is on, the numeric indicator will show 2, so on and so forth. However, the selector terminal will not allow me to wire multiply inputs into the case structure, I tried Bundle by Name, Bundle and Array to Cluster, but they did not work. I set the case structure with 3 cases, they are 1, 2 and 3.
Could someone help me please. I have attach an image and the VI of the work I did so far.
I have another question, is there a function which can toggle other switches to off when there is a switch has been toggled on.
Thank you very much
Tommy
Attachments:
Trial - Case Structure.vi ‏7 KB

Tommy, attached find a cheeseball way of doing this that has given me a LOT of mileage over the years. IT lends itself nicely to a couple of really good practices that NI recommend, but I have given you the bare-bones to "see under the hood".
The recommended practices:
1. You can make this a nice tight sub-vi where you can put it into a core library of routines that you'll use over the years, even extending the logic to look only for changes, etc.
2. If you are thinking about Front Panel design considerations, you'll want to use arrays of controls where possible, as that's a nice neat way of containerizing your switch for both the FP and Block Diagram.
Have fun. I have TONS of these types of things, so feel free to PM me if you have any other needs.
Wes
Wes Ramm, Cyth UK
CLD, CPLI
Attachments:
Boolean Switch Logic.vi ‏11 KB

How do i output multiple arrays from a case structure to create one larger array

I currently have a vi that has one hardware input that i needed to take a measurement then be moved and take a similar measurement at a different point. To accomplish this i used a while loop inside a case structure. The while loop takes the measurement and finds the numbers i need while the case structure is changed per the new measurement location. I want to take the data points i have created in each case and output them into a single table. I assumed to do this the best way would be to get the data from each case into its own built array and build a larger array but I cant get the information out of the case structure so that it all inputs at different places.
thanks for your help
Attachments:
Array.vi ‏30 KB

Hi Ross,
attached you will find a solution for your table building problem.
I would suggest thinking about program design - having the same case content in several cases doesn't make sense. I also would not want my user to press several stop buttons depending on choosen measurement...
Best regards,
GerdW
CLAD, using 2009SP1 + LV2011SP1 + LV2014SP1 on WinXP+Win7+cRIO
Kudos are welcome
Attachments:
Array.vi ‏45 KB

How can i use a string as a control for case structure?

my vi is reading data. the output is a string,how can a string can control the case structure? because the there's a constructed vi in that case structure that wll perform a tast after the main vi read.
Thank You
(Can you please give me a simple example how can do this)

Try this vi. You shouldn't have any problems just connecting a string to the case selector.
BJD1613
Lead Test Tools Development Engineer
Philips Respironics
Certified LV Architect / Instructor
Attachments:
string_to_control_case_structure.vi ‏10 KB

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
LabVIEW Champion . Do more with less code and in less time .
Attachments:
implies.png ‏8 KB

How to get a case structure to execute only once in a loop

I have a while loop that is monitoring temperature. Once the temperature meets or exceeds a given setpoint I want to start a timer. At this point I don't want to monitor the temperature anymore. That is, if the temperature should drop below the setpoint, I don't want to execute the case structure again when the temperture meets or exceeds the setpoint(the temp may oscillate about the setpoint for a given period of time). In any event, I need the case structure to execute only one time, not every iteration of the loop.

You can put a local Boolean variable "Flag" inside that case structure and
set "Flag" to False. Outside the case structure, use an "AND" function
output to control the case structure. The "AND" function has two inputs. One
goes to the comparison results between real temp and setpoint. The other
inputs connects to the "Flag" variable. In this way, once you entered that
case structure, the "Flag" will be turned to False, and then in next
iteration, you won't get into the case again because the "AND" function will
be False as your "Flag" is False now.
Hope this helps.
Rentian
1. Inside the case structure, put a
"BB Herman" wrote in message
news:[email protected]..
>I have a while loop that is monitori
ng temperature. Once the
> temperature meets or exceeds a given setpoint I want to start a timer.
> At this point I don't want to monitor the temperature anymore. That
> is, if the temperature should drop below the setpoint, I don't want to
> execute the case structure again when the temperture meets or exceeds
> the setpoint(the temp may oscillate about the setpoint for a given
> period of time). In any event, I need the case structure to execute
> only one time, not every iteration of the loop.

Repeating case structure

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