Fans- Locked Rotor vs. Speed Sensor (Tach)

What is the difference between the Locked Rotor and the Speed Sensors (Tach) on DC Fans?

Locked Rotor -
A Locked Rotor Signal is generated when the Blades of the Fan are not spinning. Example: Obstruction in the Blades or failed Bearing.

Speed Sensor (Tach) -
Speed Sensors are to indicate the speed of a fan at different operating Voltage Levels.

Please refer to the Manufacturers Data sheet for the Wire Colors that are used.