Basic Profibus Questions

[BobChuck]

I've got some basic questions on Profibus. We are looking into developing a system that uses this form of communication, but we need a few questions answered in a broad sense before we can proceed.

How fast can it reliably process a large amount of data while contained in a large multithreaded executable? Our typical executables are 7,500 KB, and have to run on a Pentium 4 PC indefinately without raising CPU above 20%. Given that constriant, and given my general unfamiliarity with the technology / protocol, how fast can we go? 100ms? 5ms? 1ms?

Do I need any special software packages? Can I expect the developer of the Profibus card to provide the needed software in LabVIEW?

We use LabVIEW 8.2.1; is it reasonable to expect  a profibus card manufacturer to have code for that version of software, or is it possible that we will have to upgrade?

[Jochen · Accepted solution]

Hi BobChuck,

Profibus boards run the protocol onboard, resulting in very low CPU usage. If you purchase a Profibus from a random vendor, you should be able to access the Profibus through an OPC server that should be provided from this vendor. In such a scenario you should expect data rates between 10 ms and 200 ms for all data (depending on the amount of data, baud rates, OPC server implementation and so on).

With a Profibus board from NI there comes a set of vis which directly interfaces the board, resulting in much higher communication speed. This can be as low as 1 ms for all data, but again this depends on several factors. Still you should expect a performance gain of x10 by using the direct LabVIEW interface compared to OPC. Additionally these boards can also be used with LabVIEW RealTime.

For more information please refer to this tutorial.

Kind regards,

Jochen Klier

National Instruments

[Orbis-Ken]

How do you set the scan rate on the master.  I am running a comsoft pxi board with NI drivers. 

My problem is that my slave communicates perfectly 500K to 12M but below those baudrates nothing. My signal waveforms are all very good but I get the red box and no communications.

Thanks,

Ken

[Sean_F]

Hi Ken,

Thanks for posting! What is your slave? At what baudrates is it spec'd to communicate?

Regards,

[Orbis-Ken]

Sean,

We are using FPGA Proficore from ADESCOM. 9.6 K to 12Mhz

Ken

[Sean_F]

Thanks Ken,

What is the size of the payload? There have been problems reported when running at low rates for large amounts of data. Any information about your configuration would also help to pinpoint the problem.

Thanks,