Is an oscillator based measurement adequate in a liquid environment?

Oscillator based measurements with quartz crystal resonators are analyzed. The investigations have shown, that classical thickness monitors and also many chemical vapor sensors based on a quartz crystal microbalance (QCM) work properly even with simple oscillators. It was demonstrated, that for applications in a liquid environment more sophisticated electronics are necessary. Also a comparison between the experimental results in liquids and the theoretical predictions is hardly possible without the knowledge of the oscillator behavior. As our solution we present an automatic gain controlled oscillator with two output signals, the oscillator frequency and a signal which is representing the damping of the quartz resonator. Further on a calibration method is introduced, which allows one to calculate the series resonance frequency f_s and the series resistance R_s from these oscillator signals