A detailed discussion is given of the effects of intermodulation caused by the nonlinearity in bridge null detector system. A resonant filter circuit with high Q value was designed and fabricated to restrain this effect. The required large inductances for the harmonic filter are realized by a winding on high - permeability porcelain jar cores, the highest Q value and lowest losses noise can be obtained by adjusting the gap of two porcelain jar. Experiment results shows that the input noise of the filter is less than 1 nV/ ?/Hz, and the error caused by intermodulation distortion effect was reduced efficiently by more than two orders of magnitude.%详细讨论了由于电桥指零仪系统的非线性而产生的谐波交叉调制效应对电桥平衡的影响,设计并制作了一种高Q值的谐振滤波器以抑制此效应的影响.谐振滤波器的电感线圈采用高导磁率的瓷罐型铁芯绕制而成,通过调节两个瓷罐的间隙的大小以获得最大的Q值,从而降低由于铁芯损耗产生的热噪声.实验结果表明,该谐振滤波器的等效输入噪声小于1nV√Hz,采用该滤波电路后,交叉调制效应造成的影响被有效降低了两个数量级以上.
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