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1、Principle of Sensors传感器原理电阻应变式传感器Resistance Strain-Gage Sensors 3.3.3、交流电桥及其平衡AC Bridge and Its Balance 交流电桥及其平衡交流电桥及其平衡交流电桥及其平衡交流电桥及其平衡AC Bridge and Its Balance AC Bridge and Its Balance 直流电桥直流电桥直流电桥直流电桥优点：优点：优点：优点：电源稳定、平衡电路简单，仍是主要测量电路；缺点：缺点：缺点：缺点：直流放大器较复杂，存在零漂和工频干扰。DC bridge DC bridge AdvantagesAd
2、vantages:The power supply is stable,the balance circuit is simple,and it is still the main measuring circuit;Disadvantages:Disadvantages:DC amplifier is complex,with zero drift and power frequency interference.交流电桥交流电桥交流电桥交流电桥优点：优点：优点：优点：放大电路简单无零漂，不受干扰，为特定 传感器带来方便；缺点：缺点：缺点：缺点：不易取得高精度。AC bridge AC br
3、idge AdvantagesAdvantages:The amplifier circuit is simple,free of zero drift and interference,and is specific Sensors bring convenience;Disadvantages:Disadvantages:It is difficult to obtain high precision.交流电桥特点：交流电桥特点：交流电桥特点：交流电桥特点：Characteristics of AC Bridge:Characteristics of AC Bridge:交流电桥由单频交流
4、电源供电，交流电桥各臂的电阻要考虑分布电容的影响，这时桥臂不再是纯电阻了，可将桥臂视为复阻阻抗，分别为Z1,Z2,Z3,Z4The AC bridge is powered by a single frequency AC power supply,and the resistance of each arm of the AC bridge should consider the influence of distributed capacitance.At this time,the bridge arm is no longer a pure resistance,but can be
5、regarded as a complex resistance impedance,which is Z1,Z2,Z3,Z4输出电压应用复数表示The output voltage shall be expressed in complex numbers 交流电桥由于引线分布电容的影响，平衡调节电路与直流电桥有明显的差别。Due to the influence of distributed capacitance of leads,the balance adjustment circuit of AC bridge is obviously different from that of
6、 DC bridge.平衡条件平衡条件平衡条件平衡条件Equilibrium condition Equilibrium condition 交流电桥平衡条件：交流电桥平衡条件：交流电桥平衡条件：交流电桥平衡条件：When working with one arm:When working with one arm:交流电桥输出为：交流电桥输出为：交流电桥输出为：交流电桥输出为：The AC bridge outputs are:The AC bridge outputs are:各桥臂阻抗各桥臂阻抗各桥臂阻抗各桥臂阻抗:Impedance of each bridge:Impedance o
7、f each bridge:式中：x 电抗、r 电阻、Z 复数的模、幅角Where:x-reactance,r-resistance,z-complex modulus,-amplitude 分别将复数和指数形式代入交流电桥平衡条件，可得到交流电桥平衡两种不同的表达形式。By substituting complex and exponential forms into AC bridge equilibrium conditions,two different expressions of AC bridge equilibrium can be obtained.下面以复数形式为例进行讨论
8、。下面以复数形式为例进行讨论。下面以复数形式为例进行讨论。下面以复数形式为例进行讨论。Lets take the plural form as an example for discussion.Lets take the plural form as an example for discussion.R3、R4为平衡桥臂，为固定电阻，Z1、Z2为两个应变片，阻值为R1、R2，分布电容为C1、C2，复阻抗分别为：R3 and R4 are balanced bridge arms with fixed resistors,Z1 and Z2 are two strain gauges wit
9、h resistance values of R1 and R2,distributed capacitance of C1 and C2,and complex impedance of:要使电桥初始平衡，则应满足：To make the bridge initially balanced,it should meet the following requirements:可得平衡条件为：The available equilibrium conditions are：交流电桥输出特性交流电桥输出特性交流电桥输出特性交流电桥输出特性Output characteristics of AC b
10、ridge Output characteristics of AC bridge 已知已知已知已知KnownKnown四臂工作，忽略分母项非线性，则近似输出特性为Four-arm operation,ignoring the nonlinearity of denominator term,the approximate output交流电桥的平衡调节电路交流电桥的平衡调节电路交流电桥的平衡调节电路交流电桥的平衡调节电路Balance adjusting circuit of alternating current bridge Balance adjusting circuit of al
11、ternating current bridge 电阻平衡电路调节Adjustment of resistance balance circuit 电容平衡电路调节Adjustment of capacitance balance circuit R5R6组成电阻平衡调节电路，改变 R6 使R1 R2 R5电阻值变化R5R6 constitutes a resistance balance adjusting circuit,and changing R6 makes the resistance value of R1,R2 and R5 change C、R组成电容平衡调节电路，改变 R 使Z1 Z2 阻抗变化C and R constitute a capacitance balance adjusting circuit.Changing R makes the impedance of Z1 and Z2 change