关于一种基于IIR陷波器和平均滤波器的改进方法，即先利用Hilbert变换计算出相位差粗值，再经IIR陷波器和平均滤波器得到相位差精确值。-About based IIR notch filter and an improved method of the average filter, i.e. first use of the Hilbert transform to calculate the phase difference crude values, and then by the IIR notch filter and the average filter to obtain a retardation exact value.