Need NI Profibus (PCI or CRIO) that can do DPV0 with 1ms process rate.

[jeremydg71]

We are aware of two options that NI offers for Profibus communication that we can consider. The first option, which we’ve currently purchased, is a PXI card (DF-Profi II-C-PCI,  NI PN# 780161-01) that will plug into our PXI chassis (RT controller PXIe-8135 w/ PXIe-1082 chassis). The second option which we did not purchase as of yet, is a C-series module that can be programmed in FPGA (cRIO PROFIBUS Master/Slave Module, PN# 781352-01). We would be using this module with MXI c-series expansion chassis that connects to our PXI system.

Our application requires our system to operate as a Profibus Master using both DPV0 and DPV1 communicating with a single Profibus Slave. The majority of the time we'll be operating in DPV0 mode where our cycle rate target is 1ms or less. This would not be an issue for Profibus on other platforms such as a PLC. However, as we’ve opened up the drivers for the PXI card option, it is documented that we should not expect to obtain a process update rate faster than 20-25ms. It appears the overhead of VISA in this instance is the issue.  

I guess we would like to verify that this is actually the case or be able to get more information on this potential limitation for the PXI card option. Second, if we need to go with the cRIO module option, we’d like to determine whether we can hit our 1ms process rate in DPV0 mode. Hopefully yes if we’re taking VISA out of the equation and using the FPGA interface. Any assistance with this would be greatly appreciated.

Thanks!

[TYtanic]

Hey Jeremy,

I'm doing a little bit of digging into this, but would you mind uploading a couple of screenshots of the code that you have going right now for the PXI Profibus card?

[jeremydg71]

Hey Ty,

I'm currently looking at the Example code that comes with the drivers. There is a note on the front panel of the master example (see attached) that says it should require about 20ms for the process rate. I'm going to be running some tests using our PXI card as the master with a single slave to see what rates we can actually achieve.

Thanks,

Jeremy

[TYtanic]

Hey Jeremy,

I'm going to talk to some of our R&D eningeers about this to see if I can get a more definite answer for you. I'll let you know as soon as I hear anything back!

[Aix-La-Chapelle]

Hi Jeremy,

Apologies for the very late response, I just was able to get this information for you:

COMSOFT says that the note mentioned in the example for PXI was about Low-Cost PXI controllers from about 10 years ago, and that they may be able to delete that from the example now.  They mentioned that depending on the performance of the PXI Controller a cycle time of 1 ms or less with LabVIEW RT should not be an issue.

Please let me know if you have any further questions.  

Again, very sorry for the delay.

[jeremydg71]

Hi Matt,

Thanks for the response. We ended up doing some benchmarking of our own and found that with the PXI controller we're using, PXIe-8135 w/ PXIe-1082 chassis, we could obtain very fast Profibus cycle rates for DPV0, much less than 1ms, which is what we needed for our application. Running test code for DVP0 at a 1khz loop rate with 1 master, 1 slave, had a processor utilization of 7% for one of the cores, also important since we have several processes that will be running in parallel. It was a little difficult to get everything configured correctly with the Comsoft Configurator software, but once it we got it setup, we've been pretty happy with the performance.

Thanks,

Jeremy