The Motion Encoder System does not Auto-ID when connected to a LabPro interface so you need to open a file.

To use a single Motion Encoder system, connect to DIG/SONIC 1 and open the file, ”
Motion Encoder System.cmbl,” in the Experiment Files>Probes and Sensors>Motion Encoder System folder.

Because the file is set up for a Motion Encoder in the DIG/SONIC 1 port, it will not work if you connect the Motion Encoder to DIG/SONIC 2.

If you want to use two Motion Encoder Systems at the same time on a LabPro, you will need to set up the second Motion Encoder using Set Up Sensors from the Experiment menu. The other option is to download the following file, unzip it, and open it with Logger Pro.
http://www2.vernier.com/til/3232/two-motion-encoders.zip

The Motion Encoder System is automatically recognized when connected to all our newer interfaces-there is no need to open a file.

See also
Motion Encoder System Troubleshooting and FAQs