I need to prevent any other operation from occurring between two triggers

[Derek at Epicor]

I have a platform that triggers a digitizer and then begins running a motor, and records the waveform as the motor is running. This occurs 25 times and the results are tallied. My PXI chassis is also running other tests at the same time. Occasionally, the time between the digitizer trigger and the motor trigger changes, and I get an inaccurate value on one or two of the 25 runs. How can I prevent any operation from occurring between the digitizer trigger and motor trigger so that the triggers always occur the same delta t? I am running a PXI 5112 oscilloscope and a PXI 7344 motor controller, with LabView drivers controlled through TestStand.

[DFGray]

Let's take a step back and look at what you are trying to do. From your message, it appears you are triggering a digitizer and motor controller from separate sources and having trouble keeping them in phase due to other tests being run at the same time (presumably eating CPU time on the controller, thus causing trigger jitter). Given the limited info, here are some options:

1. Don't run other tests at the same time. If you are using software triggers (unclear from your posting), you will need an RT system at the least to ensure determinacy. Software triggers are usually a poor choice when trigger relationships matter.


2. Use a hardware trigger from either the digitizer or the motion controller to trigger the other. I would probably trigger the digitizer from the motion controller. You are using PXI, so there should be several backplane options.


3. Use another channel on the digitizer to digitize the trigger of the motion controller. Synchronize your data analysis based on the position of the trigger pulse. This is the software version of 2, and will result in a lot more analysis code.

If this doesn't point you in the right direction, repost with more details of your experiment and we will try again.

[Derek at Epicor]

You are correct about the method of triggering. I send a start signal to my PXI 7344, then send a software trigger to my PXI 5112 to begin recording the data. Previously, this was the only test running on the PXI chassis, and I didn't have problems with the time between the start signal and the software trigger. At the time, the other tests were performed by off-the-shelf equipment using GPIB connections. Trying to streamline the process, I purchased PXI equipment to run the other equipment, not expecting to have the trigger delay problem.

#1 I need to run both of the tests, so that isn't a possibility. I'm also in a time crunch, so while using RT may be the long-term answer, it won't help me immediately.

#2 seems like a possibility, but I can't seem to find the backplane trigger function in the PXI 7344 drivers. I'll look around a little more, but if you could explain how to use the hardware trigger on both a PXI 7344 and a PXI 5112 that would help.

#3 is a possibility, but I'm the software work to get it to work seems like it would be enormous, and subject to its own set of difficulties.

Thanks for you suggestions

[Scott_R]

Derek,

To trigger on the backplane of the PXI bus, you would need to make use of the RTSI lines in the trigger routing functions. In order to trigger the digitizer from the motion controller, I would suggest using the breakpoint functions to create a breakpoint and then the Select Signal VI to route that breakpoint to RTSI 0. You could then use the triggering functions for the 5112 which can be found in LabVIEW by opening the Function Palette and navigating to All Functions >> NI Measurements >> NI Scope >> Configuration Settings >> Triggering. Also, you can use the NI-Scope express VI to set up triggering. The triggering VIs will allow you to specify RTSI 0. Therefore, you will be writing the trigger using the breakpoints and Select Signal and read the triggers with the trigger configure VIs for NI-Scope.

Take a look at those VIs and let me know if you have any additional questions on this issue.

Regards,
Scott R.
Applications Engineer
National Instruments