Pedal Assist Sensor (Pas); Torque Sensor - Evinci infinity HD Series User Manual

Pedal Assist Sensor (PAS)

In an electric bicycle, the PAS measures if the crank is moving in riding
direction. This information will be passed on the controller which then activates
the motor to support the rider. The PAS can distinguish between forwards and
backward movements of the crank.

Torque Sensor

By measuring the amount of force the rider applies to the pedals the torque
sensor signals without any delay to the controller how much support the motor
has to add. This creates are very responsive but at the same time smooth
riding experience. Torque sensors are mostly placed in the crank, with or
without the motor. They are more expensive to build than PAS sensors.
References
Ref (1): Ministry of Health NZ, Website
Notes:
18