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

Similar Messages

Reading files from shared mapped folders

How is the correct approach to read files from a volume which maps a shared disk?
I mean, we have the Y:\Folder which maps \\bla_bla\root\folder.
Our application has to read into Y:\Folder.
How do we create a File object which points to Y:\Folder?
Thanks.

> We catch a java.lang.NullPointerException
Okay. You know how to debug those, right? Some condition exists that is causing an NPE (that line alone won't do it), so you'll need to do some investigating.
How to resolve a java.lang.NullPointerException
You'll want to ensure that the directory actually exists, you've mapped it correctly, you have the appropriate permissions to access it, etc.
Good luck!
~

Datasocket read stop but shared variable can update

Hello ,
I program with datasocket open/read, sometimes the read stops and after some time,maybe 10s, it go on reading, I compare this with shared variable (DSC) and found
the shared variable can update ,I don't know what happen to my program.
( the reason I'd like to use datasocket is that I need to change the ULR dynamically , I have many OPC tags to read ( 100 PLCs time 80 tags per PLC ) )
thanks for your help!
Solved!
Go to Solution.
Attachments:
shared variable VS datasocket.jpg ‏23 KB
shared variable VS datasocket.vi ‏17 KB

Hi~
The read function waits for items to be updated, and 10ms is the default time for this waiting. Setting wait for updated value to false will probably solve this issue.
PS: URLs of variables could be changed programmatically, see this document if you like.
Good day

Problema di polimorfismo con Read/Write delle Shared variable

Salve,
Cercando di modificare l'esempio di progetto "Shared Variable Client/Server" in un progetto dove sono i diversi client a mandare dati al Server ( ovvero l'esatto contrario di quello che fa )
mi sono inbattuto nel problema illustrato nelle due figure che seguono.
Ovvero, sostituendo "Writable PSP Variable" ad "Readable" nella scheda "Connect"(FIGURA 1) mi da un errore nella scheda "Read/Write" (FIGURA 2), ovviamente anche qui ho sostituito a "Read Variable" un "Write Variable".
Mentre utilizzando il Data Socket funziona, ma non mi sono chiari i vantaggi e gli svantaggi nell'utilizzare quest'approccio.
Qual'è la strada migliore tra Shared Variable e Data Socket per creare un sistema Client/Server così costituito, ovvero con un cospicuo numero di client da servire ( destinato a crescere )che mandano simultaneamente un discreto quantitativo di dati ( circa quelli di una seriale a 115200bps ) ad un server
FIGURA 1
IMMAGINE 2

Translation
Hi,
Trying
to modify the sample project "Shared Variable Client / Server" in a
project where different clients to send data to the server (ie the
exact opposite of what it does)
I untapped in the problem illustrated in the two figures that follow.
That
is, replacing "Writable PSP Variable" to "readable" in "Connect"
(Figure 1) gives me an error in "Read / Write" (FIGURE 2), and of
course here I replaced "Read Variable" a "Write Variable.
While using the Data Socket works, but I have clear advantages and disadvantages of using this approach.
What
is the best route between Shared Variable and Data Socket to create a
client / server system so constituted, or with a large number of
customers to serve (to grow) that simultaneously sends a fair amount of
data (approximately those of a serial to 115200bps) to a server
The images points to a gmail location. It is not properly attached.

Read file from shared folder

Hi,
I want to read a file "test.txt" from the server "XY" (my own PC) with the shared folder "devices$"
I want to check first whether the file exists:
FileInfo myFile = new FileInfo(@"\\XY\devices$\test.txt");
if (myFile.Exists)
Console.WriteLine("exists");
else
Console.WriteLine("does not exist");
The result is always "does not exist" even though the file exists, why??

I tested your code, It works fine on my side. So i doubt whether the file
exists. Please check your file. Or do you have right to access the file?
We are trying to better understand customer views on social support experience, so your participation in this interview project would be greatly appreciated if you have time. Thanks for helping make community forums a great place.
Click
HERE to participate the survey.

Reading files from shared lib in WAS 5.1

I have a shared library name 'files' in WAS 5.1. The classpath is ${TEST_FILES}/shared.
I have some textfiles in that directory, not properties files. Can I read those file from that directory from Session Bean like
File f = new File("${TEST_FILES}/shared/some_file.txt");
Can't have that done. What is the right way to do it? Or is there any?

Enterprise beans aren�t allowed to access files primarily because files are not transactional resources. Allowing EJBs to access files or directories in the file system, or to use file descriptors, would compromise component distributability, and would be a security hazard.
Another reason is deployability. The EJB container can choose to place an enterprise bean in any JVM, on any machine in a cluster. Yet the contents of a file system are not part of a deployment, and are therefore outside of the EJB container�s control. File systems, directories, files, and especially file descriptors tend to be machine-local resources. If an enterprise bean running in a JVM on a particular machine is using or holding an open file descriptor to a file in the file system, that enterprise bean cannot easily be moved from one JVM or machine to another, without losing its reference to the file.
Furthermore, giving EJBs access to the file system is a security hazard, since the enterprise bean could potentially read and broadcast the contents of sensitive files, or even upload and overwrite the JVM runtime binary for malicious purposes.
Having said all this, my understanding is that the EJB file restriction can be broken if the developer really, really knows what they are doing and accepts the consequences such as those above. I did this on a recent WebSphere project and accessed files in a named directory on the application server box using the standard file IO APIs. It just meant that if the application was deployed to another server, the same directory structure would need to be recreated.
If you're working with read-only data a more appropriate way would be to store the files in a deployment JAR, and access then with the getResource() or getResourceAsStream() methods of java.lang.Class.

LabVIEW DSC 8 Alarm State shared variable

Hello,
it was possible in LabVIEW 7.xx to read the alarm state with "Read Tag Alarm".
I didn´t find such in LabVIEW 8.20.
I testet "Read Alarms" and the "property knot".
Thank you
Torsten

Hi Torsten,
to read the alarms in Labview DSC 8.20 you can use the "Read Alarms.vi" in combination with the "Format Alarm data.vi".
You are using shared varibales with DSC 8.20. There you can set the proprties (attached Screenshot.zip)
In Labview you can get these alarms with the two VIs (see above).
I also attached a little example project. There you can open the "DSC Read Alarms Demo.vi" inside of the program to see how it works.
Hope this helps
Best regards
Dippi
Attachments:
Screenshots.zip ‏227 KB
DSC_Alarms.zip ‏210 KB

Using Modbus TCP I/O Server with new DSC Shared Variables in LabVIEW 8.6

Hello,
I'm using LabVIEW 8.6 and want to communicate with a Beckhoff BK9000 Ethernet TCP/IP Bus Coupler via Modbus TCP. Instead of using the NI Modbus Library, I've tried the new LabVIEW 8.6 feature "DSC Shared Variables" as described at the bottom of this page: Latest NI LabVIEW DSC Module Features and Demos. Reading of analog input bus terminals works fine. However, I haven't figured out yet how to write on an anolog output bus terminal with these shared variables.
It's about a 16 bit analog output and I need to write to the registers 0x1121 and 0x0801. It works with the NI Modbus Library (just using function code 6 and choosing the registers), but on the other hand I don't know which shared variables I have to choose for these registers. I've tried several data items (e.g. 400001 upwards as well as 402049 for 0x0801) but none of them worked. I would be glad for a short explanation - thanks in advance for your support!
Regards
utechle

The Beckhoff documentation says, that holding registers start with 0x0800. I've checked this by using the NI Modbus Library. I used the "MB Ethernet Master Query.vi" togehter with the function code 6 for "Write Single Registers", changed the settings of the starting address to hexadecimal view and entered 801 (since it starts with a control byte in 0x0800 and the data out word follows in 0x0801). Furthermore, I had to address register 0x1121 in the same way for resetting the watchdog. As I've mentioned in my first post, this method works fine. However, I haven't found out yet which shared variables i have to use for accessing these registers.
On the other hand, it's no problem to read data from analog input bus terminals using shared variables. They start with 0x0000 (status byte) and 0x0001 (data in word) and I can read data with the shared variable and data item 300001, respectively.
Message Edited by utechle on 01-27-2009 11:12 PM

Weird delay reading shared variables

Hello,
I'm working on a project were I'm monitoring some prodution lines. I'm using DSC module's OPC server to connect to PLCs on the production line and I've created bound variables on my labview project of the PLC's tags.
On my project I have one main VI were I show information about the production lines and were I can access several subVIs were I show other information about those lines. Then I have a VI that is running in background were I'm reading about 50 shared variables from the PLC and where I'm registering some data in a MySQL database, datalogging data on the Citadel database and registering alarms.
The problem I'm having is that on the VI that runs in background I noticed a delay reading the variables that are reading containers weights from the production line. It seems that all the other shared variables don't suffer any delay, only the weight variables start having some delay when the values are increasing. It also seems like that, when I'm only running that VI alone, without running the main VI, there isn't any kind of delay. I'm reading the shared variables as shared variable nodes.
Can anybody help me understand what's happening and how can I fix this delay? The VI that runs in background is time critical and a weird delay like that messes up my data.
Solved!
Go to Solution.

Hi Mateus23,
The shared variable has various buffering capabilites, including integration with the Real-Time FIFO feature in LabVIEW Real-Time.
I guess that the buffering settings are causing the unexpected behavior.
Check these resources:
Buffered Network-Published Shared Variables (whitepaper)
Shared Variables Properties Dialog
- Network Page
- Real-Time FIFO Page
~~

Can not read shared variable on cRIO, error -1950678968 nitaglv

Hardware setup:
Laptop
Laptop connected via USB to a frammer garber.
Laptop IP: 192.168.0.2
NI vision calculating a diameter and setting a network varaible
cRIO
cRIO connected to the laptop
cRIO IP: 192.168.0.1
Project has the shared variable in the cRIO library
NI vision writes to the variable on the cRIO. I can see the variable properly updating in system manager on the cRIO. I can also run a VI in my computer that shows the variable properly updating. But...... When I read the variable with a VI running on the cRIO, I get the folowing error and the variable never updates:
Error -1950678968 occurred at Shared Variable in Main.vi
Possible reason(s):
LabVIEW: Failed to load nitaglv, which is required for Network-Published Shared Variables.
This error or warning occurred while reading the following Shared Variable:
\\NI-cRIO-OASIS\cRIOVariableLib\BubbleDiameterFromVision
\\192.168.0.1\cRIOVariableLib\BubbleDiameterFromVision
(I do not get any errors at deloyment)
So everything (NI Vision, a VI deployed on the laptop, NI Distributed System Manager) can see the variable on the cRIO being updated by the NI Vision.... Except for a VI running on the cRIO.
I have verified that I have Network Variable Engine and Variable Client Support for RT installed on the cRIO. I have tried reinstalling all s/w on the cRIO. Tried rebooting all. And talked in a nice, positive, reassuring voice to the chassis.

Hi!
I just had the same issue with my cRIO 9073 using NI RIO 3.6.0.
The problem is not caused by a corrupted project, but the improper installation of the OS on the target. There is nothing you can do using the SW installation wizard in MAX, as it does not matter if you intall a full RIO SW, minimal or custom.
You have to install the full install or a custom one with Shared Variable support. Then you have to FTP to the cRIO, and manually edit the "ni-rt.ini" file located in the root of the controller.
Make sure you have a line in the "[MODULE VERSIONS]" section which shows the version of the nitaglv.out file. (The problem is caused because this dll is not loaded when you try to access a SV) Mine looks like nitaglv.out=6.3
Then you have to insert "nitaglv.out;" without quotes to the [LVRT] section's StartupDLLs key's value. I did it after the taggerrt.out name. So my key entry now looks like this:
[LVRT]
StartupDLLs=nisysapirpc.out;NiViSrvr.out;NiRioRpc.out;taggerrt.out;nitaglv.out;sysstatepublisher.out;
memoryChecking=False
LABVIEWRTDir=/c/ni-rt/system
PATH=/c/ni-rt/system/;/c/ni-rt/;
CDIntervalTicks=55
WebServer.Enabled=FALSE
RTTarget.VIPath=/c/ni-rt/startup
RTTarget.IPAccess=+*
RTEnetRcvMode=2
RTCPULoadMonitoringEnabled=True
RTTarget.ApplicationPath=/c/ni-rt/startup/startup.rtexe
server.tcp.access="+*"
RTTarget.LaunchAppAtBoot=True
RTTarget.EnableFileSharing=True
server.tcp.serviceName="Main Application Instance/VI Server"
After you are done with the editing, you have to save the file, and overwrite the original one. You have to reboot the controller for the modification to take effect.
After this you will be able to host your variables on the cRIO and also read/write them from the application running on that same target.
I hope this will help for you too.
Regards,
Peter

Slow performance to read/write shared variables programatically

We are using datasocket read and write functions to read and write shared variables programatically (in the same machine) but we only achieve a performance of aprox. 200 reads/writes per second. We are using Labview 8.6 with DSC.
Is possible to get better results? That performance is normal?
Any help would be appreciated. Thank you in advance.

Hi MMCDAT,
I think this value can
be normal as you can see in this link:
http://zone.ni.com/devzone/cda/tut/p/id/5037
As you can see, the
limit for datasocket depends on your Ethernet limitations, even if you as using
it just in one PC:
http://digital.ni.com/public.nsf/websearch/6AC9E65734E53F9A8625672400637ECC?OpenDocument
You can improve the
performance changing the update mode or Vis configurations:
http://digital.ni.com/public.nsf/allkb/F8F7DE98856B50588625672400648045?OpenDocument
http://digital.ni.com/public.nsf/allkb/2D9C6D73A160537986256B290076456E?OpenDocument

Shared Variable Crashing LabVIEW

This is just one of those projects that has a brick wall at every turn so far. Two computers running LV2009. Computer A hosts Data Write Shared Variable. Computer B hosts Data Read Shared Variable. Data Read is bound to Data Write. Everything was working fine, and then late yesterday afternoon, I don't think I had changed anything on the shared variable, I start up my VI on Computer B, and LV crashes. The VI starts to run until the first execution of Data Read, and then poof, everything open in LV dissapears. The problem is one hundred percent repeatable since then.
Here is what I know:
1. An error indicator hooked to Data Read shows -1950679034 (Shared Variable has no value) for about a second before the crash. Everything stops executing as soon as the warning appears.
2. The Data Write is single writer, but it is also occasionally read in the VI that it is written in. It is not being read when the crash happens. I can however perform the read on Computer A without incident.
3. Not sure if this is related, but if I open the VI on Computer B, and then open the project, I am not able to drag Data Read from the project onto the block diagram. I also cannot perfrom any operations on the Shared Variable (like right click, ignore timestamp). I have to close the VI and reopen it from the project. Thinking back, this problem may have started when I opened the VI without opening the project.
I am torn between abandoning Shared Variables and trying to figure this out. I would definetely prefer to use the Shared Variable, especially because I need some buffering. I'm guessing I can buffer things some other way. Not sure if I can remotely access a queue, or ... ?
Solved!
Go to Solution.

I looked at STM, but I think the Data Socket VI's may be a better fit for me. It seems like Data Socket and shared variables are sort of intertwined, but I'm hoping DS doesn't suck as much as the SV seems to so far.
I think NIC means network interface card? Anyway, I don't really know how many I have. The Data Writer is on a PXI8108 with Windows, the reader is an old crappy Dell that I inherited with the desk.
I'm also not sure about the logos.ini file you referred to.
My intention is to transmit an array of double waveform that is about 15 - 20 channels acquired at 100 - 1000 Hz. I think the Data Socket looks like the simplest way to do this, and I could live with 100 Hz if speed is a problem, but I sort of don't think it will be. I'll try tomorrow unless somebody has a better suggestion.
By the way, I saw in another post a similar problem with Shared Variables that is supposedly fixed with the new patch for 2009, but I'm not sure I trust SV's because this will, for about thirty seconds of its lifetime, be one of the most critcal applications I've written, so I want confidence that it will work for those thirty seconds.

Read shared variable using D/3 DCS

This is a rather odd question.. I think it can be done, but I have not yet figured how.
A client has a DCS System (I believe from NovaTech), which communicates with a database.
They use a different PC to get data from a cFP using Shared Variables.
There is mention of data being sent over a Modbus Interface.
They want to know if it is possible to read the Shared Variables directly using their DCS System. If the DCS was from NI, it would probably be easier to accomplish. However, I am not at all acquainted with the NovaTech product, but I believe there must be a way to innterface to it. Probably using Data Sockets and/or PSP Protocol.
I realize the above is rather obscure... I have sent an email requesting more info and I am preparing the next email. I figured that I'd better do some background investigation and ask proper questions.
Has anyone attempted such a thing or similar? How about reading Shared Variables from Non-NI software? I did find some threads discussing reading/Writing (to/from) Shared Variables using LabWindows-CVI, but I suspect this will be quite different. Maybe I'm wrong..

Thanks Christian.
I will continue in this thread after I find out more details from the client.
RayR

Reading data from mlx90129 rfid tag chip by using spi communication with labview?

Hi,
i have evb90129 evalution board in that mlx90129 chip and external memory (cat25128) and three external sensors are there, i am logging data from chip by using rfid reader it ok i am reading. at the same time i configured spi communication and i am trying to read data i am reading data from internal memory not from external memory i tried but i didnt suceed , now can i use labview to read data from mlx chip and external memory. for spi communication i am using sparkfunction atmega168 microcontroller and also i have spi to usb cable? now can i communicate or i required any devies? is it possible?
thanks in advance,
biji.

I suspect the culprit to be the first parameter to your function actually. Calling another function requires the caller to allocate any buffer with a big enough size for the function to write something into. Allocate that array by using Initialize Array with U8 as type and the correct number as size. Pass this size also as read_length. While your code doesn't make use of this I think the third parameter to your function is either wrong or unnecessary.
As you use it now it is really nothing more than a local stack variable which you could declare inside the fucntion just as well. On the other hand what you probably want to do is have a function prototype like:
extern "C" _declspec(dllexport) unsigned char read_Sensor(unsigned *char read_data, unsigned long read_length, unsigned long *byte_transfered);
But you will have to do some modifications in your C code to support that parameter correctly.
That all said, doing the same in LabVIEW using VISA functions would have been done with about two VISA nodes, no DLL headaches and probably already long ago working.
Rolf Kalbermatter
Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions

Communicating Between Multiple LabVIEW Executables on different computer using Shared Variables

hi,
I need to develop some executables which will be launched on different computer of a LAN. Some DATA are common. I need to share the data using shared variables.
I usually used LabVIEW so I 'm familiar with shared variables but in this case, the RT target is a part of my
project.
I do I need to procceed in my case?
thanks

Ok but it's not my configuration and I haven't found my answer in the tutorial.
You speak of a case where there is a computer and a RT target under the same LabView project. As I said earlier, I often use labview RT and shared variable between computer and RT target. But I assume here it's different.
My question is : how do you acces to the SVE from 3 computers (without any RT target)?
1. If I create 3 labview projects using the same Shared Variable, do I need to use the same .lvlib on each project?
2. Is it possible?
3. How can I configure where the SVE should be? When I use a RT target, It only depends where I put my Lvlib. But here there is 3 projects.
James
Attachments:
Sans titre.JPG ‏9 KB

Labview is reading zero from shared variable

Similar Messages

Maybe you are looking for