More counters means less accuracy

[JoJoBeartheThird]

Using the code I've attached below, I'm trying to acquire on 3 channels simultaneously. When I used one channel,the numbers are perfect. But when I had a second channel, the numbers are a bit off. With three channels, all three channels are off by about 10%. I'm not sure why this is happening. My PFI38 is wired to the square wave function on my 6602. Is that incorrect? I'm not sure if the problem is my programming or if I've set up the board improperly.

Thanks.

[gus]

What version of NI-DAQ are you using? And what signals are connected to PFI39, 35, and 31? The way this VI is currently implemented, you will not be measuring the same period of your signal for each of these. All three pairs of counters will measure at different times, not concurrently. I might be able to help you some more if you can give me some more information about your system.

gus....

[JoJoBeartheThird]

Ni-daq 7.2 and there are 3 PMT modules connected to PFI39,35,31. My goal is to acquire counts from all three at the same time. Obviously, something is going wrong. Any help is appreciated; the whole dma/counter thing doesn't make a lot of sense to me.

Thanks,
Jo

[gus]

If it is possible for you to use DAQmx, I would recommend it. If not, it looks like you might be able to simply change the trigger mode to "single triggered". You may still have some issues that might require you to change the layout of your program though.

Let me know how this works for you.
gus....

[JoJoBeartheThird]

I changed the trigger mode to "single triggered" but that has had no effect. I had tried using the DAQmx earlier on this project but it did not work and a collegue suggested I do it this way.