Abstract: The sensor for liquid density measurement based on the resonance theory is driven and detected based on the piezoelectric effect and inverse piezoelectric effect in this paper. The automatic gain control (AGC) circuit based on piezoelectric excitation and piezoelectric detection with simple structure and low power consumption is designed, when the output signal of sensor changes large, the gain of excitation signal can be automatically adjusted with the output signal amplitude so that the output signal amplitude remains stable. The circuit has many advantages, for example simple structure, good flexibility and reliability, fast speed of response and so on. Meanwhile, the calibration experiments are taken, and results conform that the repeatability error is about ±0.05% and the accuracy is about 1.0kg/m³. In a word, the sensor designed in this paper can achieve liquid density measurement online with high precision in real-time.

Key words: Liquid density, Resonant sensor, Piezoelectric excitation, Piezoelectric detection, Automatic gain control