【摘要】 分析了锁相真有效值测量的工作原理,需使测量系统一直跟踪电源频率的漂移,并把工频电源的周期严格N等分,才能消除原理性测量误差。采用锁相技术能产生与电源频率锁定的倍频脉冲。用CMOS专用数字锁相芯片CD4046(内部集成有鉴相器和压控振荡器)和分频芯片CD4040构成了实际锁相电路,外加由电阻和电容形成的简单的片外积分环路滤波器。给出了硬件电路,并分析了其基本工作原理。描述了相位锁定过程,并讨论了相位锁定后的电路工作情况。实际运行证明所设计的硬件电路测量精度合乎要求。更多还原

【Abstract】 The principle of phase-lock true RMS(Root Mean Square) measuring is analyzed.In order to eliminate the theoretical measuring error,power frequency shift is tracked by measuring system for strict dividing power period into N equal sections.The phase-lock technique is used to generate multiple frequency pulse,which follows the power frequency.A phase-lock circuit composed of special phase-lock CMOS chip CD 4046 and frequency dividing chip CD 4040 is designed,with a simple external integral loop filter composed of a resistance and a capacitance.The phase-detector and the voltage-controlled oscillator are integrated in the chip CD 4046.The hardware circuit is presented,and the basic working principle is analyzed.The phase-lock process is described,and the post-phase-lock working process is discussed.Practical operations demonstrate that the designed circuit meets the requirement of measuring precision.更多还原