电磁流量计自适应极化噪声抵消系统研究

电磁流量计是一种应用广泛的测量导电液体体积流量的仪表。测量时,金属电极与电解质会发生电化学反应,产生极化噪声。极化噪声幅值远高于流量信号幅值,使电极输出信号信噪比较低;极化噪声存在漂移的现象,会影响电磁流量计变送器的信号调理工作,限制电路的放大倍数,增加ADC采样位数、电路成本、功耗等。对此,提出了一种基于前馈控制的自适应极化噪声抵消方案,设计了相应的信号调理电路,通过硬件电路实时提取和抵消极化噪声,极大地提高了电极输出信号信噪比。通过试验,验证了该方案不但能有效滤除极化噪声,而且能提高信号调理电路的放大倍数、减少ADC的采样位数、减少电路的成本和功耗。

Research on Self Adaptive Polarization Noise Cancellation System for Electromagnetic Flowmeter

The electromagnetic flowmeter is widely used for measuring volumetric flowrate of conductive liquids.During measurement,the polarized noise would be generated because of the electrochemistry reaction occurring between metal electrode and electrolyte,i.e.measured liquids.Since the polarized noise is far greater than the flow signal in amplitude,the signal-to-noise ratio(SNR)of the electrode output signal is relatively lower.The polarized noise is unstable with the drift phenomenon that the signal conditioning of the electromagnetic flowmeter transmitter is degraded for which the circuit amplification factor is restricted.The ADC sampling bits,circuit cost,power consumption,etc.are badly increased.For this reason,a self-adaptive polarized noise cancellation scheme with feedforward control is proposed,and the corresponding signal conditioning circuit is designed,so that the SNR of the electrode output signal is greatly improved by means of the extracting and cancelling of the polarized noise in real time.Finally,the test proves that the polarized noise is effectively eliminated,the ADC sampling bits are decreased,and the cost and power consumption of the circuit are reduced.