已知:直流电桥电路中U = 4 V, R1= R2 = R3 = R4 = 120Ω,若R1为金属应变片,其余为外接电阻。试求:当R1的增量为 ΔR1 =1.2Ω时,电桥输出电压 U。为多少?
如图所示
U0=Ubc-Ucd
=U*R2/(R1+R2)-U*R3/(R3+R4)
=U*(R2R4-R1R3)/((R1+R2)(R3+R4))
当增量△R1<<R1时,高阶微量可忽略。并带入R1=R2=R3=R4
则输出电压:
U0=(U/4)△R1/R1
=1V*△R1/R1
=0.01V