1769 HSC Help needed with RPM

Hello Im using a 1769 HSC card with a L35E and trying to get the RPM. Ive been reading through forums for a couple days trying all the ideas from people who have had similar issues but I still cant get the current.rate(x) working.  Im using a single channel encoder at 60ppr. I believe the card is set up right and the channel is enabled. The counter seems to work fine but the rate stays 0 when im spinning the encoder slow but will jump to  100 or 200 if I spin it fast. 

Any help would be appreciated.

Thanks