ni 6008 wrong counts

I use a ni 6008 device, to count TTL-Signalls from a descrete particle counter.

99% of the time, the ni 6008 counts are correct and the same as the particle counter, but sometimes I receive wrong counts from the ni6008.

The NI 6008 counts much more events, than the particle counter.

I suspect static electricity as a cause. The particle counter ist conected to the mains, the laptop works on batterie. the line between particle counter

and the NI 6008 is shielded.

Is there a solution for my problem?

Thank You

Jochen