Fig. 1. Schematic of FMCW interference

Fig. 2. Curves of angular frequency of reference wave and signal wave with modulation current of sawtooth wave

Fig. 3. Waveform of FMCW beat frequency signal with sawtooth current modulation

Fig. 4. Physical image of liquid level sensor

Fig. 5. Experimental system of diaphragm type frequency modulation continuous wave optical fiber liquid level sensor

Fig. 6. Flow chart of initial phase demodulation of beat signal

Fig. 7. Physical image of liquid level measurement system

Fig. 8. Linearity and sensitivity characteristics of liquid level sensor

Fig. 9. Analysis of hysteresis of liquid level sensor

Fig. 10. Repeatability analysis of liquid level sensor

Fig. 11. Stability data graph of liquid level sensor

Fig. 12. Stability analysis of liquid level sensor

Fig. 13. Stability measurement results of liquid depth of 100 mm at the same temperature

Fig. 14. Random error points of shape variable at diaphragm center when liquid depth is 100 mm at the same temperature

Fig. 15. Normal distribution of random error of diaphragm central deformation at the same temperature with liquid level depth of 100 mm

Fig. 16. Temperature characteristics of liquid level sensor