Chapter 4 designs and determines the parameters of the algorithm adopted in the instrument system . analyzes and compares the different effects to frequency estimation when using digital filters with different group delay ; determines the data length , a parameter of frequency estimation ; introduces the method of available judgment of sensing signal and determines the judgment threshold as well 第四章设计和确定了仪器系统软件算法的部分参数：分析和比较了不同群延迟特性的数字滤波器对频率估计的影响；确定了影响频率估计参数?数据长度的取值规律；给出了判断传感信号有效性的检测方法并确定了检测门限的取值规律。
