Abstract: An oscillation condition was proposed and experimentally verified for an elec-troderaeparated piezoelectric sensor (ESPS) in non-electrolyte liquid, it was ex-pressed as C_s≥2R_qωC_o²/[Y+(1+Y²)^1/2-2RqωC_o, where C_s is the solution capaci-tance, R_q, C_o and ω are the motional resistance, static capacitance and resonant an-gle frequency of the crystal, respectively.And Y＝tgθ, where θ is the phase shift inthe oscillator.The relationships between the minimum cell constant needed for ES-PS to oscillate and each of the following parameters, permittivity, density and vis-cosity of the liquid as well as the oscillator phase shift were discussed.The″ cease-to-oscillate″ frequency of ESPS was measured.The oscillation ability of ESPSin-creases with increasing permittivity or decreasing density and viscosity of the liq-uid.An oscillator with a larger Yvalue is helpful to drive ESPS.

Key words: Piezoelectric sensor, Quartz crystal, Cell constant