PXI RT transferring data over ethernet

[mbhatti2000]

I have a simple question, I just to transfer data from my RT PXI system and get it to my PC. thats all- I have used the following code. By just using this code , 50 % resources are taken. Then I used shared variables to transfer the dynamic data fromt the channels (another question mark? if I should do this) the system gives jittering.......... the trasfer is in chunks.........after using 3 shared variables (network published) the system loses contact with the PXI as 100% CPU power is used up...........what good is this PXI RT system ??? Help needed

NI-8184 embedded controller

PXI.6259 M-series Multifunction DAQ

850 Mhz processor

256 MB RAM

Host PC : windows XP

just want to tranfer the data, why is so hard ??

I also used TCP IP method.........from an exaple.........cannot transfer more that one channel............can somebody just send me or tell me what is the best method..........just want to see is the device I am testing is giving an output or not from a remote place.....in the same network...........atleast in the same Room and it connected directly to my PC right now.

[BerndF]

Hi mbhatti2000,

is your  PXI system running Windows or Real Time?

You stated in your post that you are using shared variables, in your screenshot there's no shared variable visible.

In the screenshot you have posted there are various issues visible:

- First of all you're using the DAQ assistant within a timed loop, which normally doesn't make any sense at all. What are the settings of your DAQ assistant? I presume that the timing of the timed loop interfers with the DAQ assistent settings.

- Generally it's not a good idea to use the DAQ assistant when you're programming an RT system (use low level VI's instead).

- If you're doing buffered data aquisition, you don't need an RT system at all as the DAQ board itself provides determinism by accessing the onboard timing chip.

Please provide your LabVIEW project so I can see what you're actually doing.

Regards,
Bernd

[mbhatti2000]

Hi Bernd,

My PXI system is running LV RTOS

Yes I am using SV's and they are not visible sorry for that.

I have now used low leve VI's

I need to work with RT system because this is the only system I have.

I am not interested in loosing some data.........and the task is not time crtical , just want to transfer data smoothly.

wnat to bind the SV with the data channel.

I tried what u said. I have two issues now.

First : The loop does not work smootly.........gives some jerks .............and therefore data seems to flow in chunks.

Maybe there is still some time conflict.

Second what data type should I choose the I choose double waveform (1D array but the data reviced is like lines)

[BerndF · Accepted solution]

Hi mbhatti2000, 

as I told you before: It doesn't maky any sense using a timed loop in this example!

Use an untimed  while loop instead, the timing will implicitly be done by the aquisition rate and samples to read you configure.

Before you start programming make yourself familiar with the basic principles of data aquisiton and real time programming, you'll find some useful links at the bottom of this thread. Also have a look at the examples that are shipped with LabVIEW, there are also plenty of examples to be found online.

The following screenshot shows you a very basic example of continous data aquisition where a shared variable is being used to transfer data to the host.

Also I would ask you to post your actual code, as the screenshots do not provide all the necessary information.

Complete Data Acquisition Tutorial

http://zone.ni.com/devzone/cda/tut/p/id/3116

LabVIEW Real-Time Module Training

http://zone.ni.com/devzone/cda/tut/p/id/9988

Regards,
Bernd

[mbhatti2000]

Hi Bernd.

Thanks for the reply. I implemented it. It works. There isnt smooth updates-------on the host pc it becomes fast then slow.........the upate is not smooth..........can you suggest something..........

[mbhatti2000]

i try attaching the program again

[BerndF]

 Hi mbhatti2000,

unfortunately you have provided only the project file itself, but not the VI's containained.

Remember: The data transfer from the PXI system to the host PC is done via TCP/IP, which is inherently not deterministic. As the data is transferred via the network, there might also be delays due to the network traffic.

I'm not sure what you mean when you say that "the update is not smooth". Please provide some more information, e.g. a screenshot of the behaviour.

Regards,
Bernd

[mbhatti2000]

Well the loop iteration time is not constant, that why the waveform on the chart is updated with jerks......sometimes it looks as if it has hanged for 1 sec or so then the waveform moves much faster as normal. A screen shot would not show this detail.

I build an application......... 

[BerndF]

Hi mbhatti2000,

as I told you before: Don't use a loop timer within a loop that's doing buffered analog input! The loop is timed by the data aquisition settings!

In your example you have an aquisiton rate of 10kHz and the samples to read are 1000. So that means that every 1/10s = 100ms the loop will be executed, there's no need at all for the 50ms you have inserted.

Using the split signal for displaying the waveform data also doesn't make any sense at all. Please make yourself familiar with the basic principles of programming in LabVIEW, otherwise you will hardly achieve the desired goal.

Regards,
Bernd