A variable speed wind turbine having a doubly fed induction generator includes an exciter machine mechanically coupled to the DFIG and a power converter placed between a rotor of the DFIG and the exciter machine which guarantees a stable voltage to the power converter. Transmission of light through a Fabry-Perot etalon is exponentially sensitive to small displacements in a movable mirror due to an applied accelerating force. A plurality of operating system abstraction layers are provided. The retainer is further configured to be removeably engaged with the open receptacle.