Sense means one of the methods for a living being to gather relatable information about the world; sight, smell, touch, taste and hearing. It can also be said to mean a general conscious awareness of an occurrence or event.
"I sensed his presence the moment he walked into the room."
Since refers to a specified time duration in the past. In some usages, it could mean because.
A. "Where have you been since morning?"
B. "I gave the task to the other applicant since you decided not to reply."