Steam turbine and method to determine the rotation of a rotor blade in the flow channel of a steam turbine

Steam turbine has an optical measurement system (60) for measuring the timing of a turbine blade (33) that is placed in a flow channel (25). The measurement system comprises an emitter (55) for transmission of a light beam (61) onto the turbine blade and a receiver (57) that collects the reflected light beam. Transmitter and receiver are separate entities. An Independent claim is made for a method for measuring the timing of a turbine blade in which a light emitter and receiver are set up so that the reflection angle of light transmitted, reflected by the blade and detected is greater than 45 degrees.