Fig. 1. Structure of the novel rotational speed measuring device.

Fig. 2. Geometric relationships of the two beams and the measured rotating body.

Fig. 3. Rotational speed measuring system from different perspectives.

Fig. 4. Results of rotational speed measurement: (a) 200 deg/s, (b) 600 deg/s, and (c) 1200 deg/s.

Fig. 5. Photo of radius sensitivity experiment: (a) a piece of foam, (b) two pieces of foam.

Fig. 6. Results of rotational speed measurement: (a) no foam, (b) a piece of foam, and (c) two pieces of foam.

Fig. 7. Photo of angle sensitivity experiment.

Fig. 8. Results of rotational speed measurement: (a) deflection 0 deg, (b) deflection 5 deg, and (c) deflection 10 deg.

Fig. 9. Measurement results under four working conditions.

Fig. 10. Measurement results of the hand-held tachometer.

Fig. 11. Measurement result of the vibration influence.