Champlin PD uses the ARMER digital trunking system, so make sure you are using a compatible digital scanner.
Frequency and talgkroup info for ARMER can be found here:
Allied Radio Matrix for Emergency Response (ARMER) Trunking System, Various, Minnesota - Scanner Frequencies
Champlin PD is dispatched on the Hennepin North Main, which is talkgroup ID 10002. You will hear several different PDs on that talkgroup, Champlin units are 52xx.
If you are wanting to hear the Fire Dept, Champlin shares it's FD with Anoka (Anoka-Champlin FD) and can be heard on the Anoka Co. Fire Dispatch talkgroup.