Noise Reduction Methods for Resonant Sensor Impedance Phase Measurement

In the present paper, the sources of noise in measuring the phase impedance of a resonant sensor are identified. Possible measurement methods are described in terms of their influence on the resonant sensor used. A suitable measurement method has been selected for our proposed resonant flow sensor. Subsequently, the effects of sensor connection, temperature, frequency instability of the used generator on the phase reading were simulated. From these, the corresponding uncertainties were then calculated. Active shielding was then used for the sensing amplifier, as it is necessary to reduce the input capacitance of the voltage measuring amplifier as much as possible. This affects the resonance significantly and is undesirable. Therefore, a special amplifier with active shielding and very low input quiescent current of the order of 10 ⁻¹⁵ A was used. Suppression of interference from external sources such as switching power supplies and radio signals was done by a suitable active band-pass filter. For phase measurement, the AD8302 circuit was used in a suitable circuit suppressing its nonlinearity in the vicinity of the zero phase impedance measurement. Its analog output is sampled by a precision $\mathrm{A}/\mathrm{D}$ converter and then sent to the server by the ESP32 processor. This is followed by digital signal conditioning for statistical evaluation of sensor phase changes. The results obtained show that the proposed concept is suitable for challenging low flow continuum measurements.