RT Network Shared Variable and Visa Serial Instr class

Hi,
I'm using Labview 2009 SP1 with the RT module. I've had no problems creating a RT Target application and a Host PC application which are interconnected using Network Shared Variables, until I came to the COM ports fitted to the RT Target (PXI Embedded Controller and 2 x 4 port COM cards).
I can configure and use the COM ports in the RT Target application providing I use constants to define which COM port to use, i.e. VISA OPEN function accepts hardcoded "COM2" , (VISA Serial Instr class).
But I want to pass the COM Port resource name from my host application.
Is there a suitable Network Shared Variable I can create ? or how do I change the string value (COM Port name) of the VISA Serial Instr class variable in the RT Target application ?
thanks,
Gary.

Hi there Gary,
Thanks fot the post. I think I have found something that may be if use to yourself.
http://labviewwiki.org/Functional_global_variable
This is the functional global variable.
Take a look at it and let me know what you think!
Many thanks,
Liam A.
National Instruments
Applications Engineer

Similar Messages

Need help getting networked shared variables on compact fieldpoint to work

I'm still a newbie and am trying to get Networked Shared Variables to pass from a VI running on a PC to a VI running on a Compact Fieldpoint. I created a VI that sends a message via a Networked Shared Variable and a VI that receives it. I have them both in the same project. If I run them both on the PC, it works, I can send a message string from the first VI to the Networked Shared Variable and read it in the second VI. I have the second VI turn the LED "A" on and the LED "B" off if I send the string "a", and turn the LED "B" on and the LED "A" off if I send the string "b", and turn them both off if I send anything else. It works as expected if both the VIs are running on the PC. The second VI also continuously blinks the LED "C" so I can verify that it's running.
I "deployed" the second VI to the Compact Fieldpoint as follows:
In Project I dragged the VI from My Computer (under Project: name.lvproj) down and put it under the Compact Fieldpoint name.
I right clicked on Compact Fieldpoint name and verified it was set to "Connect".
I right clicked on the second VI and selected "Deploy".
I started both VIs with the "Run" arrow. At this point I know second VI is running since the LED "C" keeps blinking. But, when I try to send an "a" or "b" nothing happens, so the VI on the Compact Fieldpoint must not be receiving the messages in the Networked Shared Variable.
I also right clicked on Compact Fieldpoint name and selected
"Disconnect". The second VI continued to run since the LED "C" keeps
blinking, but I still can't get messages to pass.
Any help will be greatly appreciated.

I got this to work. I moved the library (.lvlib) containing the Networked Shared Variable to down under the Compact Fieldpoint name. Now it works.

Using Shared Variables and Initialize Front Panel Binding (to PSP)

Hi,
I use LV DSC RT 8.2.1
I have a Vacuum System That includes signals from - Pumps failure, Valves status, Vacuum gauge, start Pump ...
Each signal is read by a FieldPoint.
All the relevant FieldPoint Channels are read by the Server (a computer in the Ethernet Network) and published to the network in the form of Shared Variables.
I have a client VI that is reading the Shared Variables published by the Server using Front Panel Binding.
Problem :
Some of the Bindings are in the mode 'Write &Read' and that causes some initialization problems.
For example - Valve #1 is Open, and then a User start running the Client VI, (the Valve #1 Status mode is 'Write & Read")
if in the VI the status of Valve #1 is closed (before running it) then the Valve status is changing to Closed.
I want the Client VI to first read the Physical status of the instrument and then to change the Value if the User changes it.
But that's seems to be a problem when using Front Panel Binding... (is it?)
I know I can Deploy a lvlib in the Client Side and Item Bind to the Shared Variables or Use DataSocket.
(Is DataSocket is a Reliable method when connecting to Shared Variables? What are the disadvantages when using DataSocket?)
What is recommended by those of you that are experienced or by NI ?
Sincerely Yours,
Amitai Abramson.

Amitai Abramson,
Hello and thanks for using the NI Forums.
I'm glad that you've read the Using the LabVIEW Shared Variable Tutorial on our website. Check out these other resources:
Network Variable Technical Overview
Troubleshooting Network-Published Shared Variables
Why Do I See Unexpected Value Change Events for Shared Variables Using LabVIEW DSC?
All You Need to Know About Shared Variables
Creating a Value Change Event for Shared Variables
Alternative Method for Using Shared Variables Between Systems in LabVIEW 8.x
What Is The Difference Between Using Shared Variables And DataSocket VIs To Access OPC Tags?
The issue that you are seeing by having "Write & Read" bound items on both the server and client side is essentially a race condition, you don't know which one is being read/written at what time. To resolve this issue I would take a look at some of the documents below.
Using a Local, Global, or Shared Variable in Parallel Loops Can Cause Race Conditions
Using Local and Global Variables Carefully
Tutorial: Local Variable, Global Variable, and Race Conditions
Locking a Shared Resource or Variable in LabVIEW Using Semaphores
You mentioned not wanting to have two sets of shared variables (one on each side), but this is a great method to resovle this issue, that, or you can develope some sort of hand shaking to prevent these race conditions.
I would suggest that in the future when using these forums you try to ask only one question per thread and make it more concise. It's hard to tackle multiple questions and such broad questions as "I want to know all the ways that I can connect to Shared Variables, and I want to know the advantages and disadvantages." I suggest this because we want you to get your questions answered and more concise questions will result in quicker and better answers.
Message Edited by Ben S on 10-01-2009 06:05 PM
Ben Sisney
FlexRIO V&V Engineer
National Instruments

Distributed application: Networked Shared Variables, Named Services (Raw TCP/IP) or Other?

Happy New Year NI forums!
I am working on a project involving mobile interacting robots. In the future it is likely the application's components may need to run on different PCs (Targets). Note: at this point in time all the components are seperate but all running on the localhost machine. Thinking towards the future I want to pick the 'best' architecture to allow all these components (VIs performing various functions) in multiple locations. For example, several VIs on the Robots, VIs on serveral PCs.
I am currently aware of using Server/Client TCP/IP using named services. My mock up works well, but is it time efficient (my time coding) I wonder.. ?
Whereas I am aware of networked shared variables which handle connections and all the parsing for the underlying tcp/ip communication. But will this be difficult the manage? I am unsure if I can associate shared variables with a VI similar to named services. I suppose I could pro grammatically create the variable upon initialization of the server component - and the client could just search the list of avaiaible variables to connect too. Downside this would require DSC module.
As you can see, I am rather unsure. Any advice would be great!
Kind Regards,
James
Kind Regards
James Hillman
Applications Engineer 2008 to 2009 National Instruments UK & Ireland
Loughborough University UK - 2006 to 2011
Remember Kudos those who help!

Hi Jason,
Thanks for your reply. I hope your enjoying NI UK as much as I did.. fun times!
I have seen the link you posted a few times before. But today, I took a better look at it.
My issue is I need several multi-client severs, i.e. many servers which allow multiple clients to connect to them.
Now the STM does have an example of this - STM mutli-client Example - Server.vi (used with the STM mutli-client.vi)
However, when a make copies of these code (to have my second server) - it refuses to run. As in , it just stops itself.
I DID change the port number, on the lister aspect of the server code. But I Am unsure what else I would need to change to get this setup to work?
One thought I had was, the FIFOs all having the same name - this probably isn't a good idea between servers.
Any suggestions would be grateful!
*please could you provide me email support
Kind Regards,
James Hillman
Kind Regards
James Hillman
Applications Engineer 2008 to 2009 National Instruments UK & Ireland
Loughborough University UK - 2006 to 2011
Remember Kudos those who help!

Network shared variables lose binding

Hello,
I am developing an application in LabVIEW that uses network shared variables to transmit data between two PC's on the same subnet. The shared variables work fine when running the VI's in development mode, however, when i build the vi's into an executable I find that they no longer work. Here is what I have found so far:
I deploy the shared variable library on the publisher machine (also happens to be the development machine) through an invoke node in the executable. NI distributed system manager confirms that this does deploy and indeed updates as it should.
For the executable on the subscriber PC I created a second shared variable library (same project) with the same shared variables and bound them to the respective shared variables from the first library by selecting enable aliasing, then bind to PSP URL and browsing to the shared variable I wish to bind it to (e.g. \\hallnet-ellm2\shared variable library\serial Number). The machines listed under browse were listed by name so when I tried this initially and it did not work I manually changed the name of my machine in the URL box to the IP address of the publisher hoping that would fix it in case the subscriber could not resolve the publishers machine alias. So now my bind URL read \\192.168.0.1\shared variable library\serial Number.
As part of the executable on the subscriber I deploy this second shared variable library. NI distributed system manager confirms that this deploys but under quality for an individual variable it has a list of issues (see attached) and the bound variable is not updating. At this point the publisher shared variables are still functioning fine. By clicking on 'edit variable' I can see that the variable on the subscriber is still bound but the PSP URL is now \\localhost\shared variable library\serial number. Changing the PSP URL on the subscriber to \\192.168.0.1\shared variable library\serial number enables the variable to update as expected.However by this time my executable has already picked up the error and does not function.
I think that the issue lies with the bind URL used on the subscriber as for some reason it does not keep the binding configured in the project and instead changes to 'localhost'. Why is this? Should it not stay bound to the address specified in the project?
I have tried changing the IP addresses in the aliases file so that
[My Computer]
My Computer=localhost
becomes
[My Computer]
My Computer=ip of local machine
This did not help.
The shared variable libraries are included in the build spec to go into the support files directory and they are successfully deployed from there on both publisher and subscriber.
I am using LabVIEW 8.6 on Windows XP
Thanks for any help you may be able to offer,
Lee
Attachments:
distributed system manager.JPG ‏74 KB

Hi Lee,
I hope you are well. Thank you for your post. Your application sounds very interesting.
Looking at your issue I was wondering, have you tried lowering your firewalls, as this may be causing the problem.
Also, another option would be to setup a private network. Do you have access to any routers that you could use to link the two machines independent of your IT's infrastructure?
The other thing to try is two other computers entirely. Again, it would be ideal to take them off the network you are on, but it's something to try if my prior suggestion doesn't work. It should work on the original two machines though, and it's likely that different computers won't solve your problems because I suspect the network.
Remember that the client variables must know the location of the variables on the server, so you can't move the server exe around without changing this value.
Make sure to set the network location in the "Bind to Source" option for the client variables.
It is also possible to write a separate piece of code to install on every machine that is responsible for deploying the library and by doing so eliminate the need for programmatically deploying the variables in the original application. However, this won't really help you, because the variables you use in the application have to be the same as the ones deployed in the library, so if you change the library, they'll no longer be linked and they won't receive data. You'd have to create a separate exe for every binding source you wanted to link to, and then have a second, known library for the sake of communication locally on the computer between the ‘deployer’ and the actual application. The main application could then be assigned the responsibility of launching the correct ‘deployer’' if it sees it needs to switch to a different variable binding source. This method is not the most streamlined or effective, but it might work.
Just to let you know, you will need to use the DSC toolkit.
Please find below some knowledge base links that I think you will find helpful in your application.
Using Shared Variables in Executables
How do I Programmatically Change the Data Binding Source for Shared Variables?
I hope this information helps and if you can give these suggestions a go and let me know how you get on, that would be great.
Kind regards,
Prashant M
Applications Engineer
NI UK & Ireland

Network Shared Variable: Aliasing not working

Hello!
I am running a cRIO 9075, which is publishing network shared variables.
I can see and modify them within Distributed System Manager.
Unfortunately I am not able to read/write the variables through labview.
What I have done so far:
Tools -> Shared Variable -> Register Computer, using the IP of the cRIO
Adding a Variable to the project. Type = Network-Published, Enable Aliasing, choosing "Browse" to select the variable (all published variables from cRIO are shown there), Access Type = read/write. The PSP-URL is: \\192.168.10.70\WaveformManager\Op
Trying to read the variable results code -1950679034 and the result is always the default value for that data type.
BUT this works: using the VIs Data Communication / Shared Variable / Read/Write Variable and typing in the same URL the Distributed System Manager is showing is showing (in my case: \\192.168.10.70\WaveformManager\Op)
So, what am I doing wrong? Did I forget something or misunderstand how "Aliasing" works?
Thanks!

hi,
in which way to you read your shared variable? If you read it before you write a value "into" the variable it may couse this waring.
Have you tried this?
http://digital.ni.com/public.nsf/allkb/7DBC2C3E95AFD85C86257442005CF74C?OpenDocument

Inconsistent Network Shared Variables

I will eventually be implementing a controls program on a machine using cfp. Before the cfp gets here, I am getting practice in network shared variables by trying to pass shared variables between two VIs on my computer. I have attached the two VIs and a screen shot of my project. I run a queued state machine and after the initialization routine is done, I run the control portion of the program. The control program is titled 'The4Mprocedure2.vi' and the QSM is titled '4M_QueueDrivenStateMachine'. In the initialization routine of the QSM, 'FALSE' is written to the boolean network shared variable, 'Run_4M_Procedure'. After the initialization routine is done, and a set of certain parameters are met, the QSM writes the value 'TRUE' to 'Run_4M_Procedure'. Ideally, The4Mprocedure2.vi would read the shared variable, and when the value is 'TRUE' The4Mprocedure2.vi would run. The4Mprocedure2.vi has a case statement that causes to run the program when 'Run_4M_Procedure' = TRUE. The4Mprocedure2.vi does not run when the variable is FALSE.
The problem that I am having is that The4Mprocedure2.vi does not always recognize that the value of my shared variable has changed. When the QSM passes the value of 'TRUE' to the controls program, The4Mprocedure2.vi will sometimes still read the network shared variable as FALSE. Sometimes, I have to restart the controls program several times while the QSM is running to ensure that 'TRUE' is passed to the controls portion. Why does my controls program not recognize when the network shared variable changes values?
Message Edited by tquintana55 on 07-14-2008 11:04 AM
Attachments:
The4MProcedure21.vi ‏87 KB
ProjectScreenShot1.JPG ‏68 KB
4M_QueueDrivenStateMachine1.vi ‏131 KB

Hi tquintana55,
I believe your Issue is related to the methods that LabVIEW subscribes to the shared variables. Here is a link to a related article:
How to Avoid the "0" Value at First Read of a Shared Variable in LabVIEW 8.5.x?
To resolve this you can move your Run_4M_Procedure inside the while loop.
Sappster

Shared Variable and classes

Hi friends,
1.can you tell me the Disadvantages of Shared Variables?
2.What is classes ,how to make it?
Raj

Hi! Raj
Shared Variables
shared variables share data between loops on a single diagram or between VIs across the network. For doing that they break the LabVIEW dataflow paradigm.
Disadvantages:
1. Using variables allows for race conditions and incurs more overhead than passing the data by wire(break the LabVIEW dataflow paradigm).
Race conditions happen when you, for example, write data to a shared resource from multiple operations faster than you read data from the same shared resource.
2.You must have a project open to create a shared variable
You can also read more about shared variables at http://zone.ni.com/devzone/cda/tut/p/id/4679
Attachments:
Race condition.PNG ‏57 KB

Network shared variables reconnecting network dropout

I've got a cRIO unit communicating with a Laptop using Network Shared Variables, with one of them being a 21 index array that is buffered.
The system connects and communicates fine, but occassionally the wireless card in the laptop is losing the signal from the WAP attached to the cRIO.
When this happens the Network Shared Variables never "reconnect" and start receiving values again once the Wireless link is restored. Is this an expected behavior?
When I tried using another industrial WAP instead of the laptop wireless card I do not get the drop-outs.
Ryan Vallieu
Automation System Architect
Solved!
Go to Solution.

Hello Ryan,
Thank you for contacting National
Instruments! I have looked into the issue you are experiencing and
wanted to ask you a few more questions. First of all, do you have a
time frame in which you allow for the reconnect? I believe that the
Shared Variables should regain connection after a short period but it
will not necessarily be a very quick process. It may take a few
minutes for the Shared Variables to reconnect.
The other
thing that may be happening is if you have error wires being passed
through the Shared Variables, it is possible that the error is not
being cleared and so it will always see the error and therefore never
reconnect. In this case you will have to filter this error out and
then clear the error in order to utilize the shared variables again.
If
you have any more specific information about your program that may help
us determine the reason for this behavior. Also a screenshot of your
code would also be helpful. Please let me know if you have any further
questions and I will be happy to assist you. I hope this helps!
Thanks!
Bob H
Applications Engineer
National Instruments

Network Shared Variable Description

Hi,
I've created alot of Network Shared Variables through Project Explorer...and i have also added a description for each one in the shared variable properties screen
Could someone please tell me how i can get access to the description through LabVIEW?
Many thanks
Mike

Hi attached is a sample of code in which i am viewing a value and also its description.
Ideally id just like to have the channel name once and the description and value be taken off that, rather than if i ever change it , then have to change the input to the description and also the variable displaying the value. Hope that makes sense
Regards
Mike
Attachments:
opctest3Kep for forum.vi ‏19 KB

Network-Shared Variable - read string with CVI

I need to read an NSV string with CVI. I have been digging into accessing and writing NSV with CVI, but they are all scalar value. What should I do with strings, clusters and arrays?

'm an employee at National Instruments and I wanted to make sure you didn't miss the Network Variable API that is provided with LabWindows/CVI, the National Instruments C development environment. The the Network Variable API will allow you to easily communicate with the LabVIEW program over Shared Variables (http://zone.ni.com/devzone/cda/tut/p/id/4679). While reading these links, note that a Network Variable and a Shared Variable are the same thing - the different names are unfortunate...
The nice thing about the Network Variable API is that it allows easy interoperability with LabVIEW, it provides a strongly typed communication mechanism, and it provides a callback model for notification when the Network/Shared variable's properties (such as value) change.
You can obtain this API by installing LabWindows/CVI, but it is not necessary to use the LabWindows/CVI environment. The header file is available at C:\Program Files\National Instruments\CVI2010\include\cvinetv.h, and the .lib file located at C:\Program Files\National Instruments\CVI2010\extlib\msvc\cvinetv.lib can be linked in with whatever C development tools you are using.
Thomas N.
Applications Engineer
National Instruments

Error during launching executable with network shared variables

Hi,
I am launching an executable which deploys network shared variables before running the application, I am getting the follow error. can someone tell me whats going on.
thanks,
Attachments:
Untitled.png ‏28 KB

Mudda,
Is LabVIEW 2010 installed on the PXI chassis or was this program developed on a different computer?
If LabVIEW 2010 was installed on a different computer you may need the 2010 runtime engine on the controller. If the development environment is installed on the PXI controller then you should be fine.
How are you connecting to the PXI chassis is it on the network or do you have it directly connected to your development computer?
If you look at this forum the same error occured when another device on the network was sharing the same IP address.
http://forums.ni.com/t5/Real-Time-Measurement-and/Deployment-Completed-With-Errors-Network-Shared-Va...
Could you try plugging the PXI chassis in directly and see if that resolves the issue or changing the IP address?
Kyle Hartley
RIO Product Support Engineer
National Instruments

Problem with dsc shared shared variables and error 1950679023

I'm having trouble using shared variables on my laptop PC (with Windows XP) using Labview 8.2 and DSC. I've set up a simple project with one VI and one shared variable library. In the VI, I have a while loop that writes a number from a front panel control to the shared variable. Another loop running in parallel reads the shared variable and displays to an indicator on the front panel. The VI resides on my PC (no remote targets). This program executes just fine on my desk top PC; however I get the following error codes out of the shared variable nodes when I run the project and VI on my laptop for the write and read, respectively: ni_tagger_lv_Write 180121604 ni_tagger_lv_Read -1950679023 I've tried to manually deploy the shared variable library without success. The NI knowledge base and other entries on this forum suggested that the Windows firewall should be disabled for a quick fix, however, the firewall was already disabled on my lap top. I didn't see any entries regarding the 180121604 error code.
Any suggestions would be appreciated.

The problem has mysteriously gone away. For about the 10th time, I manually deployed the share variable library, and it started to work properly.

Question about shared variables and report generator

I have a project with about 200-250 shared variables and at every 12 hours i want to make a report containing information about some boolean and double front panel variables linked to the shared variables... Now, i've tried with both the "Write Trace to SpreadSheet File" function from DSC->History and with different functions from NI Report Generation Toolkit. My problem is this: i would like to get my xls file to contain just the timestamps when my shared variable changed value. As it is, the number of rows in the file depends, obviously, on the sampling interval given as input. As an example, in 12 hours, my shared variable would change value maybe 5-6 times. Thus i would like my xls file to contain just 5-6 rows with those 5-6 changes. If i set the sampling interval to say, a matter of seconds, that would mean too much unneeded information in my xls file. Instead, if i set it to let's say 15 minutes, i would probably lose the moment the shared variable changed value. Is there a way for me to achieve my desired functionality with functions from DSC or Report Generation Toolkit? Thanks in advance, Sabin

Hi Mike and thanks for the reply. Actually, my first idea was exactly this: in an event case structure, whenever my variable changed value, i would retain the relevant data in an array and then at the 12 hour period write all of it in a report. However, my boss deeemed it memory unefficient and compelled me to use only one function. Thus my predicament... If you have more advice on this new info, i would be grateful... Cheers, sabin

Not able to access Network Shared Variable when deployed in PC

Initially, when we deploy a Network Published Shared Variable in PC and try to access the same (Read/Write) from RT, we get an error/warning "-1950679023". But when we access the same variable from the PC, it works fine. In the distributed system manager, we can see the variable getting deployed. Also the value changes in Distributed System Manager if we write a value from PC. The attached image "Shared variable Issue.png" will give more understanding of this issue.
The other way round it works fine i.e deploying in RT side and accessing from both RT and PC is working fine.
We also see that the network adapter settings is not loading properly in MAX, if at all we install any software in RT. With no software installed, it loads properly.
The following were the steps that we tried to solve the issue.
1.Flushing the entire NI software and Re- installing again
2.Formatting the RT(PXI).
3.Removing the EtherCAT Card and testing.
4.Checked the network properties of the RT network.
5.Checked the IP/Subnet/Gateway settings.
6.Checked Firewall Settings, If Shared Variable Engine is accessible.
Attachments:
Shared variable Issue.png ‏491 KB

First Root cause needs to be identified before any actions.
I would suggest first check if you can access the shared variable hosted in PC from RT using other ways like using SVE API (Logos and PS protocols, Datasocket etc..)
Check if antivirus or firewall is playing...
Check the same experiment with some other PC if you can.
You can also try creating another Shared Variable in RT and binding the same to the PC and try to access it...
Since you have did all the reinstallations already
Best Regards,
Vijay.

RT Network Shared Variable and Visa Serial Instr class

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