Data logging via Profibus DP, Sample rate about 100ms

[_EMG_]

Question about a datalogging system connected over Profibus DP:

The PC acts as DP-Master and must sample a pool of data with a sample rate minimun of 100ms.

On the PC the data is also shown on a graph. This works fine al well, but starting another process on the PC like MS Excel or just the Windows calculator, the logging loop needs about 700ms cycle time!!

On the PC is running W2k with LV7.1

Had anyone such a problem? How did you solve it?

Or is there any special programing concept needed?

Thanks in advance!

[unclebump]

try this thread.

http://zone.ni.com/devzone/conceptd.nsf/webmain/28A6979ECA9A0CAF862569050053D92D

[Jochen]

Could you please provide some more information? What type of Profibus board are you using? How do you access it (OPC, DLL,...)?

Best regards,

Jochen Klier
National Instruments Germany

[_EMG_]

I´m using a CP5613 Profibus-DP Master card from Siemens. It is accessed over OPC.

Kind regards

[Jochen]

Unfortunately this is a kind of a "worst case scenario" for time critical control applications. OPC is based on COM/DCOM and that means that you are using a huge MS protocol stack which might be disturbed easily by other processes running under Windows.
I don't know if this is possible with the CP5613 but I would recommend using a lower level communication layer like calling DLLs to communicate with the device. Please refer to the Siemens documentation and check if there is a documented API based on a DLL.

If exchanging the board is an option for you I recommend using the Comsoft DF Profi II profibus board. I have worked with this board several times and as it provides native LabVIEW support (also for LV RT and LV under Linux) the performance is superior to any other solution that I have worked with (including the CP5613).

Best regards,

Jochen Klier
National Instruments Germany

[_EMG_]

Hi!

Thank you for answering. I think I´ll try to get that card for testing. Maybe in further applications we´ll use it.

The problem is solved now. The PC acts now only as a datalogger, the graph is "outsourced" to another PC.

The PC that I´m programming on is a bit older by now (PIII with 1,1GHz and 512 MB RAM and bad graphic adapter). This might be a reason to for the problem I wrote before, too.

Thank You!