电阻-电容-电感的测量仪

R、L、C测量仪-1-R、L、C测量仪（桂林理工大学广西桂林421001）指导老师：肖老师摘要：把R、L、C转换成频率信号f，转换的原理分别是RC振荡电路和LC电容三点式振荡电路。单片机计数得出被测频率，由该频率计算出各个参数值，数据处理后，送显示。关键词：RC振荡电路LC电容三点式目录第一章系统设计··························································································31．1设计要求························································································31．1．1设计任务··············································································31．1．2技术要求··············································································31．2方案比较························································································31．3方案论证························································································41．3．1总体思路··············································································41．3．2设计方案··············································································4第二章主要电路设计与说明···········································································52．1TS556芯片简介·················································································52．1．1芯片的顶视图及各引脚的功能···················································52．1．2芯片的等效功能方框图及工作原理·············································52．2CD4066芯片的简介···········································································72．3测XR的RC振荡电路·········································································72．3．1用556时基电路构成多谐振荡器················································72．3．2测量电阻的电路模块·······························································92．4测XC的RC振荡电路······································································102．5测XL的电容三点式振荡电路·····························································11第三章软件设计························································································11第四章系统测试························································································124．1测试仪器······················································································124．2指标测试及误差分析·······································································124．2．1电阻的测量·········································································124．2．2电容的测量·········································································134．2．3电感的测量·········································································13第五章总结······························································································13参考文献····································································································13附录········································································································14R、L、C测量仪-2-附录1元器件清单······················································································14附录2程序清单·························································································15附录3总体电路图······················································································17附录4印制板图·························································································18附录5系统使用说明···················································································19第一章系统设计1．1设计要求1．1．1设计任务设计并制作一台数字显示的电阻、电容和电感参数测试仪，示意框图如下：1．1．2技术要求基本要求（1）测量范围电阻100Ω～1MΩ电容100pF～10000pF电感100µH～10mH（2）测量精度+5％（3）制作4位数码管显示器，显示测量数值，并用发光二极管分别指示所测元件的类别和单位发挥部分（1）扩大测量范围（2）提高测量精度（3）测量量程自动转换1．2方案比较目前，测量电子元件集中参数R、L、C的仪表种类较多，方法也各不相同，这些方法都有其优缺点。电阻R的测试方法最多。最基本的就是根据R的定义式来测量。在如图1.2.1中，分别用电流表和电压表测出通过电阻的电流和通过电阻的电压，根据公式/RUI求得电阻。这种方法要测出两个模拟量，不易实现自动化。而指针式万用表欧姆档是把被测电阻与电流一一对应，由此就可以读出被测电阻的阻值，如图1.2.2所示。这种测量方法的精度变化大，若需要较高的精度，必须要较多的量程，电路复杂。R、L、C测量仪-3-能同时测量电器元件R、L、C的最典型的方法是电桥法（如图1.2.3）。电阻R可用直流电桥测量，电感L、电容C可用交流电桥测量。电桥的平衡条件为12()()12nxjjnxZZeZZe通过调节阻抗1Z、2Z使电桥平衡，这时电表读数为零。根据平衡条件以及一些已知的电路参数就可以求出被测参数。用这种测量方法，参数的值还可以通过联立方程求解，调节电阻值一般只能手动，电桥的平衡判别亦难用简单电路实现。这样，电桥法不易实现自动测量。Q表是用谐振法来测量L、C值（如图1.2.4）。它可以在工作频率上进行测量，使测量的条件更接近使用情况。但是，这种测量方法要求频率连续可调，直至谐振。因此它对振荡器的要求较高，另外，和电桥法一样，调节和平衡判别很难实现智能化。图1.2.4用阻抗法测R、L、C有两种实现方法：用恒流源供电，然后测元件电压；用恒压源供电，然后测元件电流。由于很难实现理想的恒流源和恒压源，所以它们适用的测量范围很窄。很多仪表都是把较难测量的物理量转变成精度较高且较容易测量的物理量。基于此思想，我们把电子元件的集中参数R、L、C转换成频率信号f,然后用单片机计数后在运算求出R、L、C的值，并送显示，转换的原理分别是RC振荡和LC三点式振荡。其实，这种转换就是把模拟量进拟地转化为数字量，频率f是单片机很容易处理的数字量，这种数字化处理一方面便于使仪表实现智能化，另一方面也避免了由指针读数引起的误差。1．3方案论证1．3．1总体思路本设计中把R、L、C转换成频率信号f，转换的原理分别是RC振荡电路和LC电容三点式振荡电路，单片机根据所选通道，向模拟开关送两路地址信号，取得振荡频率，作为单片机的时钟源，通过计数则可以计算出被测频率，再通过该频率计算出各个参数。然后根据所测频率判断是否转换量程，或者是把数据处理后，把R、L、C的值送数码管显示相应的参数值，利用编程实现量程自动转换。1．3．2设计方案该设计方案的总体方框图如图1.3.1所示。R、L、C测量仪-4-图1.3.1设计的总体方框图第二章主要电路设计与说明2．1TS556芯片简介方案选择中，利用555时基电路构成多谐振荡器来测量电阻R、电容C，为了测量两个物理量需要两块555时基电路，为节省一部分硬件空间，以一片556时基电路来代替。2．1．1芯片的顶视图及各引脚的功能556双时基集成是COMS型的，内含两个相同的555时基电路，它的顶视图如下图2.1.1所示，双列直插14脚封装。图2.1.1555时基电路顶视图顶视图各引脚的功能分别为：1、13脚：放电；2、12脚：阈值；3、11脚：控制；4、10脚：复位；5、9脚：输出；6、8脚：置位触发；7脚：GND；14脚：+电源Vcc。2．1．2芯片的等效功能方框图及工作原理芯片的等效功能方框图如下图2.1.2所示，由于556双时基集成块内含两个相同的555时基电路，它的等效功能方框图与一个555时基电路的等效功能方框图相同，在下面的分析R、L、C测量仪-5-中，可就12个556芯片单独分析。图2.1.2555时基电路等效功能方框图芯片的工作原理12TS556的等效功能框图中包含两个COMS电压比较器A和B，一个RS触发器，一个反相器，一个P沟道MOS场效应管构成的放电开关SW，三个阻值相等的分压电阻网络，以及输出缓冲级。三个电阻组成的分压网络为上比较器A和下比较器B分别提供23Vcc和13Vcc