A new vibration membrane-type liquid density sensor that is based on resonance theory is presented in order to measure
the density of different kinds of liquids. This sensor, which consists of resonant membrane, exciter, and signal picking
system, possess the advantages of easy fabrication, excellent repetition, high stability and fine resolving ability. Density
of the liquid is measured by comparing the natural frequency variation in air and liquid respectively. In this paper, the
calculating model of the sensor is simplified with one degree freedom system, in which equivalent mass me and
equivalent elasticity coefficient ke are all of importance. Finally, density of water is measured at 20°C by this sensor.
The measured natural frequency in air and water is 5359 Hz and 3769 Hz respectively. Corresponding Q factor (quality
factor) of the sensor is in the range of 500-600. Experiment results have shown that this sensor has good repeatability
and it is a kind of effective method to measure the density of liquid.