Abstract：A very low noise 24-bit analog-to-digital converter that is deployed in a new scheme of signal processing circuit for the electromagnetic flow meters enables the feasibility of using only one stage DC-coupled instrumentation amplifier. This method can overcome the unavoidable loss in the common-mode rejection ratio in the conventional AC-coupled amplifying circuit, and keep low enough circuit noise while having ultra-high input impedance, therefor improve the resolution of the flow measurement. The new scheme is able to accept 450 millivolts DC difference on the sensor electrodes, has extraordinary input dynamic range and excellent linearity. The prototype has achieved ±0.2% of reading on range 0.5 to 5 meters/second in the flow calibration test.
2018, Vol. 28 