数字电桥测量LC谐振特性

Measuring the resonance characteristics of LC circuit with digital electric bridge

了解LC电路的谐振特性是核磁共振激发或检测实验的关键,为此介绍了在使用数字电桥测量LC电路的幅频和相频特性中,既要了解交流毫伏表的测量局限性,又需理解电压与电流之间相位差的物理含意及其重要性.同时,基于物理原理和数学描述,理解直接测量和间接测量或显示量之间关系,而最终实验显示结果可能是由复杂的数据处理分析所得.实验结果表明:LC并联谐振可实现电流放大功能,更适合于核磁共振激发;LC串联谐振具有电压放大作用,有利于核磁共振检测.本工作拓展了LC谐振特性的实验测量方法,帮助了学生认识到最终实验显示结果可能并非直接测量原始数据.

The resonance characteristics of LCcircuit were the key properties for effective excitation or detection of nuclear magnetic resonance.The aim of measuring the amplitude-frequency and phase-frequency characteristics of the LCcircuit with digital electric bridge was not only to understand the importance of the phase difference between voltage and the current,but also to realize the limitations of AC voltmeter.The relationship between direct measurement and the displayed data was described based on the physical principle and its mathematical expression,the final results may be obtained after complex analysis.The results showed that the parallel LCresonance could realize current amplification for the excitation of nuclear magnetic resonance,and the series LCresonance could act as voltage amplifier for the detection of nuclear magnetic resonance.This work not only extended the measurement methods of LCresonance characteristics,but also helped students to realize that the final results may not be the raw data directly measured.