Helmet Impact Testing using NI digital output device to trigger data acquisition from analog inputs

I have a really interesting project in which I am performing Helmet Impact tests using Matlab (ver 2015b) & Data Acquisition toolbox.

I have a NI compact DAQ with 8 modules. Modules 1-7 are analog input devices (NI 9234 for accelerometers / 9239 for angular rate sensors); Module 8 is a NI 9481 on which I am using a digital output to trigger a relay, which in turn activates a mechanical release to drop the helmet and start data acquisition.

But am encountering a problem trying to trigger the digital output and acquire 1 second of data from the analog inputs at 12,800Hz.

I find that I can either trigger the digital output, in which case I acquire only 1 data sample on each of the 21 analog input channels, or comment out the digital output, in which case I can acquire all 12800 lines of data.

The entire test takes less than 1 second.

Any help / suggestions would be most appreciated.

My m-file (testdaq) is attached

Thank you John