Labview Shared Variable configuration

I need some help with my labview shared variable configuration.
In my setup I have a PC running with my lvlib on it. This PC is NOT my development PC. The application deploys the lvlib. My program is I can't see those variables on my PXI RT Controller. I have the shared variable engine installed on the PC. But I can NOT add my realtime system to it. When I enter in the IP address it just doesn't add it or give me an error msg or anything. Anyone have any idea what's going on?

Hi Zorro,
I need a little clarification of the particular situation.
1) You said this is not your development machine. What software do you have on your development machine? Did you make an installer, and install it onto the host?
2) Which PXI RT controller and chassis do you use?
3) Do you have Measurement and Automation Explorer on your host? And can you see your controller there? Can you ping the device?
Brian K.

Similar Messages

How do you synchronize accesses to a LabVIEW Shared Variable?

I would like to create an ad-hoc weather station program (I'll explain more in a bit). I am using LabVIEW 8.0 Full Edition, and I would like to share data over a network between stations with the LabVIEW Shared Variable. Here's what I want to be able to do:
A node would start up, and begin publishing data to a network via a shared variable.
The shared variable is an array of clusters
The cluster information would hold things like:
Station Name
Station Location
Weather information cluster (temperature, rainfall, windspeed, wind direction, etc...)
Timestamp of last update
When a new node would like to enter, it would bind to the shared variable, grow the array, and add its information.
If a node's Station Name and Station Location is already in the shared variable, it would merely update the information in the cluster.
Viewing nodes could pop in, bind to the shared variable, and read/display the information at any time.
I am trying to enumerate problems with this before implementing, and I have run into a stinker of a problem that I am not sure how to solve. How do I synchronize accesses to the LabVIEW Shared Variable? If I read the variable, modify it, and write it back, I will undoubtedly run into a race condition where 2 nodes attempt to update its data and I will lose the data written by the first node - Node A reads, Node A modifies, Node B reads, Node A writes, Node B Modifies, Node B Writes, and thus the modifications made by Node A are lost. In my specific application losing some data isn't critical, but if not remedied this type of problem could cause massive amounts of data to be lost when there are numerous nodes, and that is definitely not acceptable.
Does anyone have any recommendations on how to synchronize the read-modify-write operations on the data in the Shared Variable?
-Danny

Wendy,
I am afraid Semaphores are not network-shared objects (to my knowledge), they are system-level objects that use operating-system synchronization mechanisms. If I were synchronizing on a single machine, a semaphore might be a valid mechanism; as an aside, most user-mode semaphores are designed to synchronize within a single process - to synchronize between processes you need to store the semaphore in the Kernel, and to synchronize over a network you would need a network node to handle serialization of requests. My Shared Variable is published over a network, and to my knowledge there are no network-published synchronization mechanisms available - mostly because there is no way to currently perform an atomic test-and-set on the Shared Variable (am I correct?) and there isn't a mechanism for blocking access to a Shared Variable from another network device/machine (or is there?). I've been looking for some way to implement an atomic test-and-set but I am running into a wall; I know that if I select the "single writer" attribute of the Shared Variable I can get LabVIEW to force a single writer allowing me to have an atomic "set", but I need more than that.
If only there was a network-shared Semaphore or some way to block other network accesses to the Shared Variable I would be in business - something like what I want doesn't exist, does it?
Thanks!
-Danny
Message Edited by texasdiaz on 02-23-2006 02:52 AM

I/O direction of LabView shared variable?

Can I programmatically change the I/O direction of a LabView shared variable? I'm using LV 2010 and I'm trying to change the I/O direction of a NI 9403 module programmatically. Is this possible?

Hi JAF,
I'm assuming your intended purpose is to input and output data through the same DIO line.
In that case, I would recommend using a case structure. You would need to create a case for input data and another case for the output.
Below is a link describing the characteristics of a case structure.
http://zone.ni.com/reference/en-XX/help/371361G-01/glang/case_structure/
I hope this helps. BTW, are you using a cRIO? I'm just curious.
Regards,
Josh L.
Applications Engineer
National Instruments

Read LabVIEW shared variables ( network variables?) with VB6

Hi, i need to read some LabVIEW shared variables (network variables?) using a VB6 program.
Is it possible?
I think that yes, using Measurement Studio for VB6 but I don't know how and I haven't found information in the Measurement Studio for VB6 help file
Could some one send me a program example or explain me how it is possible to read LabVIEW shared variables fromVB6?

Hello quintella,
To be able to interface with LabVIEW
Shared Variables with Visual Basic 6 you will need to use NI Measurement
Studio, which ships with examples on how to use VB6 with DataSocketing. Apart
from Data Sockets, if you are using Measurement Studio 8.1 or higer, with the
Network Variable Library introducted in NI Measurement Studio 8.1, you can read
and write to shared variables in ANSI C, Visual Basic .NET or Visual C#. (http://zone.ni.com/devzone/cda/tut/p/id/4679)
Here you have two links where you can
find more information about how to use the datasocket option. In addition, there
are several examples included in Measurement Studio with Network Variables and
Datasocket.
http://forums.ni.com/ni/board/message?board.id=230&message.id=2945&requireLogin=False
http://forums.ni.com/ni/board/message?board.id=230&message.id=3324&requireLogin=False
Regards,

How can I use an Access front end and Access button to control a LabView Shared variable boolean?

My company has invested a lot of money on the office network to write many many access databases and front ends. I'm looking for a way to tie a button on an access front end to toggle a LabView boolean shared variable to notify me when they changed something on their side of the network. I'm not seeing anything that helps on a web or forum search. They don't like the idea of a separate labview control that they have to push a button on to let me know.
Thanks
Solved!
Go to Solution.

Hi Patrick,
While this is not the intended purpose of Network-Published Shared Variables, you might be able to accomplish this by writing separate accessor VIs for reading from and writing to the variable, making sure to wire the inputs and outputs. Then, you could build a DLL, making sure that you include the accessor VIs as Exported VIs and include the DLL Library in the Always Included section of the DLL Build Specifications. During this process, you will define the function prototype, which will provide the function call, required parameters, and return values. Once the DLL is created, you can then call it and its functions from another programming language (C, C++, C#, VB, etc.). This may or may not work, but it is the only way that I can think of at this point. I have included some references that may help you in this process.
Building a Shared Library in LabVIEW (White Paper)
Calling LabVIEW VIs from Other Programming Languages (White Paper)
Calling LabVIEW DLL From C# (Forum with Examples)
I hope this helps.
Regards,
Mike Watts
Product Marketing - Modular Instruments

Error -1950679035 When Using the LabVIEW Shared Variable

While communication of PLC & labview 2014 SP1 via modbus ethernet I am getting continuously Error -1950679035 as per attachment.
Also distribution manager system is not responding while expanding of shared variable library. And it is not showing list of variable.
Please share some solution.
Attachments:
error.png ‏263 KB

If the Distributed System Manager isn't running, then something is seriously wrong! Has it ever worked? Have you ever had a successful deployment of Shared Variables? Have you recently installed a new version or updated LabVIEW? These questions are designed to see if something "broke", or possibly never worked in the first place ...
Bob Schor

Labview shared variable

Can any body help me in reading analogue shared variable read in LabVIEW 2009 dynamic event structure. I have tried to read the above tag through Tag Reader VI but i have experienced too much delay in first read for real data i.e. Plant data from PLC. when this particular VI executes it take minutes to display the data. if some needs its code i can provide it. Thanks in advance

First one is On value Change Event Structure
and Second one is Through Read Tag
Attachments:
On value change event.vi ‏24 KB
Read Tag.vi ‏20 KB
On value change event2.vi ‏22 KB

Error codes for shared variables in Labview 8.5?

I am trying to use Shared Variables in Labview 8.5 to enable real-time loops (similar to some of the examples in "Using the LabVIEW Shared Variable", published Aug 28, 2007). I created it to hold the result of a 16-channel A/D converter (so a 16-element I16 array). To avoid losing samples, I used buffering, with a buffer of 5. To test this, I made a pair of VIs, one a producer that stuffs a 16-element I16 array into the shared variable "every so often" (controlled by a timed loop), and a consumer loop that reads the shared variable and does something with the data.
If I think of the buffered shared variable as a Real Time FIFO (as the article suggests it is), I was curious how I would know (a) when the queue was empty, and (b) if the queue had overflowed. Both are necessary if this is to be a practical means of exchanging data -- you want the producer and consumer to run more-or-less at the same rate, but only the producer is deterministic. The consumer needs to be able to run "faster" if it falls behind (for example, because it is writing data to disk), but you don't want it to read data from the shared variable if there's nothing there. [One can always read a shared variable, after all -- as the article states, it simply "holds" the last value written to it].
Snooping around, I discovered that there are "error codes" associated with the shared variable. In particular, a code of -2220 (FFFFF754) seems to signify an empty queue (or a shared variable that has not yet been written to), while a code of -1950678981 (8BBB003B) appears to be "buffer overflow".
Is this documented anywhere? Are there other "error codes" that would be helpful to know? Is there some rationale to these seemingly-random numbers? [It would help to develop code to utilize shared variables if there was a bit less "magic" and "mystery" involved].
For what it is worth, with a buffer of size 40, I could generate 16 I16 values at 1 KHz (simulating sampling from a 16-channel A/D at 1 KHz) and pass it to a consumer node that (a) read from the shared variable until it was empty, then (b) "went to sleep" for 20 msec (simulating "doing something else non-deterministically"), and not miss any data (because I could then empty the Shared Variable RT-FIFO, which should have been half full, before it overflowed on me). Not bad throughput -- I bet I could push it even higher.
Bob Schor

Hey Bob,
The errors are documented in the LabVIEW help:
Shared Variable Error Codes
Real-Time Shared Variable Error Codes
There are several error messages for buffer underflow/overflow depending on the settings of the network or RT FIFO buffers. In particular the -2220 and -2221 are useful for the producer/consumer use case. For example (as you probably know) the consumer can flush a variable using the error code (see the attached image).
Gerardo
Attachments:
variable1.png ‏3 KB

Labview is reading zero from shared variable

Hello everyone
-I have a problem in labview shared variable cause it reads only zero value for all inputs and outputs and timers in S-1200 ...etc
but in NI OPC server using quick client it reads the correct value but when adding them in labview project they are not reading the correct value and only retruing zero
any suggestions
Thanks

Hi,
I recently finished the commisioning of the system I started to work upon. Hence the delay to come back to this thread.
During the commissioning of the system, I was concentrating on finalizing the system functionality and was using only the PC#1. Now when all the system functions were finalized, we duplicated the changes to PC#2 and started the operation.
What we observed when the PC#2 was started, was that if we were to open the same HMI page as in PC#1, the operation of the HMI was very sluggish. When we selected a different page for both PC#1 and PC#2, the HMI operation was good, all operations seemed to happen in real time!!
To give a background of the HMI, we have a subpanel to which the desired HMI page/screen is loaded. This loads a VI related to the HMI page.
Here, I am guessing that when I load the same page in both the PCs, the read/write operations to the shared variable(it is the same in both PC, and is deployed in a library on the cRIO) are some how hindered due both PCs trying to access the same network resource from different locations.
Is this guess correct? Any work arounds or solutions? Do I need to post any more information?
Thanks in advance,
Regards

How to use shared variables with native c programs

Hello
What is the way to use shared variables with native c programs?
I have a c/c++ program that uses the NIDAQmx C-API to perform measurements. Now I want to communicate to a LabVIEW program via shared variables.
Is there a C-API for shared variables as there is for the NIDAQmx functionality? Where can I find further documentation? The document "Using the LabVIEW Shared Variable" mentions that one "can read and write to shared variables in ANSI C", but there are no hints about how and where to look.
Thanks in Advance

Hi user42,
with CVI 8.0, you cannot create or configure shared variables. However, you can read or write to an already configured LabVIEW 8.x shared variable from CVI using the DataSocket API.
In order to do this you need to have and DataSocket 4.3 or higher installed.
Here's a forum post about using the DataSocket functions a LabVIEW Shared Variables:
http://forums.ni.com/ni/board/message?board.id=180&message.id=24569&requireLogin=False
With CVI 8.1 and Measurement Studio 8.1 it's possible to use Shared Variables via the Network Varaiable Library (check out the end of the "Network-Published Shared Variable" section within the "Using the LabVIEW Shared Variable" documentation and the following link).
Datasocket with LabWindows/CVI and LabVIEW Real-Time:
http://digital.ni.com/public.nsf/allkb/CC4343488413A2F586256E6200099638?OpenDocument
Daniel
NIG

Use shared variables with FPGA device on Host PC

Hi all I am having a frustrating problem. I am trying to use shared
variables linked to a cRIO 9012. The shared variables were created and
then written to in a RT vi. is there any way I can assign locations to
these not within a RT vi. I altimately need to run the Host vi on a
TPC-2512 touch panel computer and I can't run a RT application on that. I
just need the variables to update without the RT vi running and I can't
figure out how to do that, if its even possible. Here is what I have so
far. Thank you in advance for your help.
Attachments:
PumpMonitoringDevice.zip ‏2083 KB

Adam:
You may be able to use arrays to speed up your program, but bear in mind that the TPC is pretty much guaranteed to be slower than your computer (as it's likely to have lower system specs).
You'll want to use the array manipulation functions to combine and retrieve your data (most useful will likely be "Build Array" and "Index Array," see context/LabVIEW help for more details). Once you have the data in an array, you can likely pass it through a shared variable configured for an array datatype.
I'm not sure if/how much of a speed boost it will give you, but I think it's definitely worth trying. If you're not sure about the speed, try simply cutting your variable count in half and see what kind of speed increase you get with the same amount of code but fewer variable values being transmitted through your network connection.
Good luck!
Caleb Harris
National Instruments | Mechanical Engineer | http://www.ni.com/support

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

NI Visa - Shared Variable Engine

Hi,
I am using labview Shared Variable Engine to create variables on my workstation and bind them to variables on my server.
I have labview 8.2 installed on my workstation and labview 8.5 installed on my server.
The communication between them worked perfectly and I was able to use the variables created in the workstation.
In my application I need yo use NI visa to take serial input. So I installed the NI Visa on my workstation and the NI visa worked.
However, the Server was not able to see the variables I have created in my workstation.
Does this mean that NI visa do not work in parallel with the Shared Variable Engine, or does the NI visa change some of the settings parameters that would stop the Shared Variable Engine from working properly.
Thanks in Advance

This information helps me get a better idea of what you are doing, but I need much more information in order to help pinpoint what is happening in your application. You should absolutely be able to use VISA as well as the Shared Variables concurrently. What is the device that you are using for data acquisition? I'll need the model of the device. What kind of data are you acquiring? How are you using VISA to communicate with your instrument?
One other item is to look in the distributed system manager to see if your shared variables are actually getting updated
Any code you could post here would help as well.
National Instruments
Applications Engineer

Shared Variable Deployment and Hosting

Hi all,
I am writing a labview RT application where a host PC will communicate with a RIO 9074 to write/update some 400 I/O simultaneously..
I have decided to write an entry level VI on the host PC so that I can pass all data to the RIO and then receive the processed data back. Here is my question... Where should I create the network shared variables in my project?? Under the host PC or under the RIO target?? What would be the difference between hosting the network shared variables in my host PC or hosting them in my cRIO??
Cheers,
Harry

There are some questions you need to ask yourself before you make those decisions. The following tutorial has that covered under the title 'Recommendations for Shared Variable Hosting Location'. Have a look and let us know if you have any further questions:
Using the LabVIEW Shared Variable
Adnan Zafar
Certified LabVIEW Architect
Coleman Technologies

Modbus I/O server & Shared Variable Engine

小弟做專題用到Labview，想請教一個問題，目前是用labview對智慧電表讀取資料
主要用modbus I/O server(TCP/IP模式)和shared variable engine
但是網路上大多數資料是教學如何建立I/O server和設定shared variable
小弟想知道背後理論是什麼？
例如：labview如何對modbus TCP/IP的封包進行處理，並取出所要資料。
謝謝各位指教

建議使用 google
關鍵字 = labview shared variable concept

Labview Shared Variable configuration

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