A sensor assembly comprises a base plate and a sensor member displaceable relative to the base plate. A spring arrangement operates in first and second stages in response to displacement of the sensor member relative to the base plate. Different resolutions of force and torque measurements are associated with the first and second stages. A light sensitive transducer senses displacement of the sensor member relative to the base plate and generates corresponding output signals. A collimator directs a plurality of light beams onto the light sensitive transducer so that the light beams strike different pixels of the light sensitive transducer to sense displacement of the sensor member relative to the base plate.