Feedback on Getting Started with CompactRIO - Logging Data to Disk

[MechDesignAdam]

Hi,

Yes I just tried it and works perfectly. I assume this is running on my laptop, but in the example where I used the fpga method I deployed it onto the compact RIO, is that right? So is it a problem with the TDMS on the 9073? I can see the tdms.out within ni-rt/system on the RIO, don't know if that helps. 

Thanks

Steve

[Dave.C]

Hi Steve,

What version of LabVIEW Real-Time are you running on the 9073?

[MechDesignAdam]

I'm sorry a noob when it comes to this stuff, how do I find that?

Is it under Ni Max , then remote systems and software - NI-RIO 12.0.1 November 2012? Or is that something else?

Thanks

Steve

[JPP]

If you are using scan interface to test this on the Rio, then it will be running on the Rio. On the project tree, your VI should be below the Rio.

Also your data should save onto the Rio's flash drive if this is the case.

Do you have a good reason not to use the scan interface ?

[MechDesignAdam]

Ok JPP thanks for clearing that up. So before I had the VI under my computer in the project tree, and I was getting data, could see it with a chart and save it using the TDMS system.  I moved it under the RIO in the project tree, I am now not getting any data stored. It creates the file, but it is empty and no errors. When I use probes and highlight execution to see what is happening I can see data coming from my channel and going into TDMS write. As I say when I had it running in my computer it stored the data just fine.???

I need to display more ignorance here and say, I wanted the FPGA to work because it was my understanding it would be faster at data gathering if I were to have a load of strain gauges, add in some accelerometers and thermocouples etc. We are not sure what the next project will bring. My thoughts were that the FPGA runs lots of things in parallel and so can handle this sort of variety without complaint. I want our system to be able to gather data as fast as possible, or different sorts of data. I realize a large part of speed is my coding, and it does leave a lot to be desired but if I can understand how this system works I will be well on the way to my goals.

I value your opinion on this.

Thanks

Steve

[JPP]

The scan mode works up to 1kHz and on some chassis you may be limited to channel count, but it is not necessary to write any FPGA code to interface to the modules, which is a big advantage.

I recently did an application that took 16 strain bridge channels, 6 analogue voltage, 1 counter/timer, GPS  data and a handful of digital IO for pushbuttons to control the system. This operated at 200Hz, the limitation not being the scan mode, but the write time of the TDMS file to disk (!)- you can read my posts further back in this thread to read that story. 

[MechDesignAdam]

Interesting, so what is the advantage of FPGA? Seems a whole lot more complicated. Using the scan interface is more like the data aquasion systems I have used in the past so I am more comfortable with it, if you think it works just fine then I can carry on with that for now.

Any idea why the TDMS write is not working when I moved it onto the RIO?

Thanks

Steve

[JPP]

I found this paper that explains the tradeoffs with scan mode:

http://www.ni.com/white-paper/7338/en/

How are you accessing the recorded file ? If using FTP on your PC it is necessary to use view->refresh, otherwise the PC will simply load an old cached copy of the file. I spent hours troubleshooting compactRIO code that was actually working fine, because of this Windows 'feature'.

[MechDesignAdam]

Yup, thank you it was exactly that ...copied to new location and there it was....perfect.

So I now have a system up and running, but from the article you linked to it seems if I want more flexability and speed(not sure I understood all that part) I need to get the FPGA up and running.

I will get this scan interface working so we can do some data logging and annalysis, and then focus on the fpga program. So any idea about those errors I was getting when I did the FPGA prog? -2519 TDMS Open in Gather Data.vi

Thanks for all your help

Steve

[JPP]

You're welcome. Glad you got it working. BTW, if the controller has a USB port, all you need to do to log data to a USB drive is use 'u' as the drive letter instead of 'c'. Easy as that.

Yes, if you want to go beyond the 1kHz limit, then FPGA code is required. That said, you can use both- some modules on scan mode and some on FPGA mode.

Not sure what the -2519 error was...