I quote my training Manual:
Functional Description(FLAP SKEW DETECTION SYSTEM)
There are eight flap skew sensors that interface with the FSEU. The number in the name of each sensor relates to the flap drive mechanism that the sensor connects to.
The excitation power for the sensors on the left wing is independent from the excitation power for the sensors on the right wing. Also, the wiring for the excitation power goes through each sensor.
The FSEU uses the data from the flap skew sensors to monitor the alignment of the TE flaps. The FSEU compares the data from symmetrical sensors. If the difference in the position of two symmetrical sensors is more than a limit, then there is a skew condition.
If the TE flaps are in a skew condition, the FSEU sends electrical power to the bypass valve. This stops the hydraulic operation of the TE flaps.
Also, during the skew condition, the FSEU sends an input to the flap position indication control. This causes the needles in the flap position indicator to be 15 degrees apart. The FSEU compares the skew sensor data to the flap position transmitter data to determine how to split the needles. If the skew sensor position is more than the position transmitter position, then the FSEU makes the needle for the skewed flap move 15 degrees in the extend direction. If the skew sensor position is less than the position transmitter position, then the FSEU makes the needle for the skewed flap move 15 degrees in the retract direction.