Coriolis mass flow and density sensor actuation using a phase-locked loop

This paper reports on novel feedback based actua-tion electronics that use the voltage from the induction track of a Coriolis mass flow sensor as input signal for a phase-locked loop. The phase-locked loop consists of a phase detector that measures the difference between the actuation voltage and the induction voltage from the Coriolis mass flow sensor. A voltage controlled oscil-lator is directly tuned by this phase mismatch and synthesizes an harmonic signal for actuation. Therefore, the frequency of the signal synthesized by the phase-locked loop will gradually be adjusted to the resonance frequency of the Coriolis mass flow sensor, making it more robust to disturbances. Besides, waveform shape and amplitude can be easily altered. First experimental results show that the phase-locked loop controls the frequency as a function of density for different fluids. Stability is tested for nitrogen and shows a standard deviation of 0.14818 Hz for 20 ks.