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Bertec Force Plate Trigger and Syncronize with Natural Point Cameras and Labview

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  • Bertec Force Plate Trigger and Syncronize with Natural Point Cameras and Labview

    I know it should be easy, but I'm still a Labview novice. I need to collect data from 3 Bertec force plates and syncronize them with natural point cameras using the sync pulse from the OptiHub. Because I have 3 plates, I also need to syncronize two Daq cards so they sample at the same time. Has anyone done this or could get me started with the VI and give me some tips on how to trigger and sync everything together?

    Thanks!

  • #2
    Re: Bertec Force Plate Trigger and Syncronize with Natural Point Cameras and Labview

    Hi Andrew,

    I've never worked with a OptiHub before, but have quickly glance through its user manual online...please find below a few suggestions you may want to try.

    1. It seems that under OptiHub's Synchronization Control Panel, you could configure the External Sync Output Type as "Recording - Pulse".

    2. Connect this digital pulse to the PFI line on your DAQ devices.
    You may find this video very useful http://www.ni.com/academic/students/...triggering.htm

    Two more recommended text:
    http://www.ni.com/white-paper/4329/en#toc4
    http://www.ni.com/white-paper/11549/en

    You can double check your system configuration with your local NI representatives, they usually response very quickly to technical questions like this.

    Hope this is useful. Good luck with the project.

    Comment


    • #3
      Re: Bertec Force Plate Trigger and Syncronize with Natural Point Cameras and Labview

      Thanks for the info. I am curious about whether or not I need to lock the daq cards together to use the same clock, or if splitting the sync pulse from the optihubs and running to each Daq will work the same way. I am waiting for the 2nd Daq to arrive before I can start troubleshooting, but will update the post with the VI and what worked once it's completed.

      Originally posted by hlau65 View Post
      Hi Andrew,

      I've never worked with a OptiHub before, but have quickly glance through its user manual online...please find below a few suggestions you may want to try.

      1. It seems that under OptiHub's Synchronization Control Panel, you could configure the External Sync Output Type as "Recording - Pulse".

      2. Connect this digital pulse to the PFI line on your DAQ devices.
      You may find this video very useful http://www.ni.com/academic/students/...triggering.htm

      Two more recommended text:
      http://www.ni.com/white-paper/4329/en#toc4
      http://www.ni.com/white-paper/11549/en

      You can double check your system configuration with your local NI representatives, they usually response very quickly to technical questions like this.

      Hope this is useful. Good luck with the project.

      Comment


      • #4
        Re: Bertec Force Plate Trigger and Syncronize with Natural Point Cameras and Labview

        Once you think that you have everything synchronized you'll need to test the data collection and system performance to make sure that everything is really synchronized.

        You can check the force plate and 3D synchronization by dropping a small 3D marker onto each of the plates while the 3D system is capturing data - this will generate a small impulse when it strikes the force plate and by looking at the marker trajectory you will be able to determine the degree of synchronization for the 3D system and the force plate.

        Don't forget to test the synchronization over a period of time - don't just drop a marker onto the plate at the start of data collection and declare that the system works. Repeat the test after running the data collection system for as long as you expect to be recording and drop the marker just before the end of the recording. This will test that the system is synchronized over the entire period and that synchronization is not drifting ... that is, synchronized at the start of the test but then slowly loosing sync over a period of seconds.

        If you have an EMG system then you'll need to test its synchronization too - just connect a small loudspeaker (salvaged from an old radio for example) to the EMG system inputs. Then place the loudspeaker on the force plate - it will now act as a microphone and produce an EMG level input, suitable for the EMG system, so that you can compare the synchronization for the EMG data to the 3D and force plate data.

        When you tap on the force plate with the loudspeaker on the plate, this will generate a small vertical force and at exactly the same time, a small impulse will be detected by the loudspeaker/microphone connected to the EMG input. Make a recording from the force plate and EMG system and you will be able to measure any delay between the data from the force plate and the data from the EMG system.

        Comment


        • #5
          Re: Bertec Force Plate Trigger and Syncronize with Natural Point Cameras and Labview

          Originally posted by Dr_Drew View Post
          Thanks for the info. I am curious about whether or not I need to lock the daq cards together to use the same clock, or if splitting the sync pulse from the optihubs and running to each Daq will work the same way. I am waiting for the 2nd Daq to arrive before I can start troubleshooting, but will update the post with the VI and what worked once it's completed.
          Hi Andrew,

          It depends on whether you want the DAQ boards to be truly synchronised or not.
          But if your DAQ boards have a multiplexed architecture (which I'm guessing they are?) - meaning they do not support simultaneous sampling - then nothing will be "truly synchronised" no matter what we do with the connections. So splitting the sync pulse and running it to each DAQ will be sufficient.

          or alternatively, if you're using PCI devices, you could wire the sync pulse to one device and share this internally to the second device across a RTSI cable. (another US$35 from NI !!)

          May I ask which DAQ boards are you using? also curious as to why you went for 2 DAQs rather than just 1 with enough input channels for your application.

          Look forward to seeing your working VI!

          Comment


          • #6
            Re: Bertec Force Plate Trigger and Syncronize with Natural Point Cameras and Labview

            The feedback from everyone has been fantastic. Thank you! I have now moved away from multiple daq cards and swallowed the cost of a new card capable of 32 channel capture. I would still like to capture the shutter pulse from the cameras and use a clock to syncronize the data (or at least as verification that data are being sampled with the shutter timing), but the creative methods here are probably good enough considering the application. My knowledge of Labview is improving, but I'm still not able to do everything I want. I'll post the VI and other information once I get the bugs worked out and am satisfied with the solution.

            Originally posted by hlau65 View Post
            Hi Andrew,

            It depends on whether you want the DAQ boards to be truly synchronised or not.
            But if your DAQ boards have a multiplexed architecture (which I'm guessing they are?) - meaning they do not support simultaneous sampling - then nothing will be "truly synchronised" no matter what we do with the connections. So splitting the sync pulse and running it to each DAQ will be sufficient.

            or alternatively, if you're using PCI devices, you could wire the sync pulse to one device and share this internally to the second device across a RTSI cable. (another US$35 from NI !!)

            May I ask which DAQ boards are you using? also curious as to why you went for 2 DAQs rather than just 1 with enough input channels for your application.

            Look forward to seeing your working VI!

            Comment


            • #7
              Re: Bertec Force Plate Trigger and Syncronize with Natural Point Cameras and Labview

              I know it's been awhile. I have spent a lot of time trouble shooting force plate errors and working with Visual3D to model the movement. I have found some very interesting problems with my current approach.

              First, I thought everything was working great, but now that I've been processing pilot data there are many questions and problems. The camera sync always starts, but during a long capture, the signal becomes unreliable and drops out entirely sometimes. I was initially using this to start and stop my capture in Labview, but it was unreliable. Second, I appear to be getting erroneous data from the analog data file recorded in Labview. I still haven't figured out if this is a problem of my .vi, or if there is truely something wrong with the FP Amps or FP. I have found that there are many more problems than one might anticipate when trying to merge mutliple software/hardware platforms from various companies. We are very close to a solution (I think). I've posted my current .vi, and would love some feedback, especially because I think there may be some problems with how it's sampling the channels that may cause the errors in my datasets. If anyone is a labview expert, I would appreciate feedback.

              Thanks
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