Problem - digital trigger edges slowing down on fast rotations

[stefo83]

Hi, all. I have problem to figure out. I want to measure strain with two strain gages on 90 degrees (NI 9237 Half Bridge II) and I have motor with metal plate on it with 52 tooth (gear) to measure on every tooth the strain. For rotation I use NI 9401 digital input.

I need for example 1000 samples from first digital edge to second. ( on metal plate). I try start trigger. In slow speed (turn around with hand) of metal plate everything is OK. But if I turn around metal plate fast digital trigger edges slowing down. For one cycle on metal plate on slow speed cout me 52 digital edges 1000 sampels per edge (metal plate is with 52 tooths), but on fast speed count me 25 edges. Is that problem coming from syncronise of digital input and analog input. I made example with DAqmx express Vi. I set up on Digital imput and then count me every tooth independently from speed and everything is OK, but when i buid trigger for strain on fast rotation speed trigger edges slowing down.

Can anyone help me with that?

Thanks previously.

[johnsold · Accepted solution]

It looks like you are collecting 1000 samples at 10000 samples per second. That takes 100 ms. If your trigger edges occur faster than 100 ms apart, some of them will be missed.  If you are rotating your toothed plate with 52 teeth faster than one cycle every 5.2 seconds, some of the triggers will occur before the previous data collection is finished.  

What is the fastest speed that you will sping the metal palte?

Lynn