The invention relates to a sensor assembly for use in a bearing including at least one bearing cage configured to accommodate at least one rolling element of the bearing, the sensor assembly including a driven oscillator circuit providing a receiver, a function generator and a primary coil, and a passive oscillator circuit including a temperature dependent capacitance. The passive oscillator circuit is configured to be attached to the bearing cage such that the inductor coil interacts with the primary coil of the driven oscillator circuit. It is proposed that a directional coupler is provided in a signal line between a function generator and the primary coil of the system, wherein the directional coupler is arranged to output a signal reflected from the passive resonant circuit in the cage toward a tuned receiver receiving the feedback of the signals generated by the function generator.