Beginner timing program - triggering with photogates

Question

Hello, 
  I am attempting to create a program in which I can time the sprint time of runners that break photogates, which are connected to channels on the measurement device. The idea is that once the photogate is broken, there is a voltage trigger that begins a timer, and the timer stops once the the next photogate trigger is broken (another voltage trigger). I have something very basic attached in which if a voltage threshold is surpassed (from one channel), a time is taken, and then potentially when the next threshold is surpassed, another time is taken, and perhaps the two times can be subtracted, but I can't seem to make this work out of the program, thus it is not quite exactly what I am looking for. I am very new to LabView and I think the solution might be simple, but I can't seem to work it out. Could you give me any suggestions?
Thanks for any help.
Attachments:
sprintspeed_timer2.vi ‏33 KB

Answer 1

For the program to do what you want you only have to have it remember all the times it triggered - in my example I used a shift register with an array for that.
There are a few things to be aware of (maybe more than I'll think of now):
1. Windows is not a real time OS - your measurement may be off by a couple of microseconds. If it has to be exact doing the timing in software will not suit you.
2. If you can live with that you still have to be careful with that timing VI. It counts to 2^32 - 1, and then it starts over. That might happen during the time you want to take.
Regards Florian
Attachments:
sprintspeed_timer2_array.vi ‏25 KB