一种用于电容式电磁流量计的励磁系统研制

Development of an excitation system for capacitively-coupled electromagnetic flowmeter

信噪比低与干扰类型复杂一直是阻碍电容式电磁流量计产品化的关键因素。针对交变励磁磁场对流量信号产生微分干扰与同相干扰的问题,建立了矩形波励磁系统的等效电路并分析了励磁电流的动态特性,结合分析结果与常见励磁电路在电路结构与功耗方面的优劣特点,提出通过缩短励磁电流过渡过程提高流量信号信噪比的方法。为了实现该方法,研制了基于电流模式PWM全桥逆变器的励磁系统,并结合流量计标定装置与流量信号检测系统进行实验验证,实验结果表明该励磁系统可为传感器的磁路提供更高的励磁参数,能在增大流量感应电压信号的同时有效抑制微分干扰与流动噪声。另外,该励磁系统为电容式电磁流量计的传感器与转换器中流量信号检出部分的研究奠定了基础。

Low signal-to-noise ratio and complex interference types are the key factors that block the way to the com- mercialization of capacitively-coupled electromagnetic flowmeter. Aiming at the problem that the alternate exciting magnetic field generates differential interference and in-phase interference to the flow signal, an equivalent circuit for square-wave excitation system is built, and the dynamic characteristic of the exciting current is analyzed. Considering the analysis results, and the advantages and disadvantages of common exciting circuits in circuit structure and power dissipation, an approach is proposed, which can improve the signal-to-noise ratio of the flow signal through shortening the transient process of the exciting current. In order to implement this method, a PWM current-mode H-bridge invert- er based excitation system was developed. In order to testify the validity of the approach, the flowmeter calibration sys- tem and flow signal test system were used to carry out the experiments on the excitation system;and the experiment results show that the excitation system can provide better excitation parameters for the magnetic circuit of the sensor; when increasing the exciting current, voltage and frequency simultaneously, the flow signal increases;meanwhile, the magnetic-field-induced interference is suppressed to a certain level. Moreover, the excitation system also lays a foun- dation for the further development of capacitively-coupled electromagnetic flowmeter.