G R(S)o C(s) -H2 图2-34某系统的信号流图 解:前向通路有3个 1→>2→3→)4→5→6B=G1G2G3G4G5△1= 1→>2→>4→>5→6P2=G1G6G4G5△2=1 →2→3→6B3=G1G2G7A3=1+G4H 4个单独回路 4→54L1=-G4H1 2→3→6→2L2=-G2GH2 2→4→5→62L=-G6G4G3H2 2→3→4→5>6>2L4=-G2G3GG3H L1与L2互不接触 L12=G4G2G7H,H A=1+G,H+G2G,H2+GG4GSH2+G2G3G4GSH2+G4GsG,H,H2 C(s) B<(PA+P42+f43) G,G,GG, G,+G,GG,G,+GG,G 1+GH,+G2G,H2+GG4GSH2+G2G3GGSH,+GG, H,H, 例2-14系统的方块图如2-35所示,试画出信号流图,并用梅逊公式求系统的传递函数 R(s)47 1 2 3 4 5 6 R(s) C(s) G1 G2 G3 G4 G6 G5 G7 − H1 − H2 图 2-34 某系统的信号流图 解：前向通路有 3 个 1→ 2 → 3 → 4 → 5 → 6 P1 = G1G2G3G4G5 1 =1 1→ 2 → 4 → 5 → 6 P2 = G1G6G4G5 2 =1 1→ 2 → 3 → 6 P3 = G1G2G7 3 =1+ G4H1 4 个单独回路 4 →5 → 4 L1 = −G4H1 2 → 3 → 6 → 2 L2 = −G2G7H2 2 → 4 → 5 → 6 → 2 L3 = −G6G4G5H2 2 → 3 → 4 → 5 → 6 → 2 L4 = −G2G3G4G5H2 L1与L2 互不接触 L12 = G4G2G7H1H2  =1+ G1H1 + G2G7H2 + G6G4G5H2 + G2G3G4G5H2 + G4G5G7H1H2 4 1 2 7 2 6 4 5 2 2 3 4 5 2 4 2 7 1 2 1 2 3 4 5 1 6 4 5 1 2 7 1 1 2 2 3 3 1 ( ) 1 ( ) ( ) G H G G H G G G H G G G G H G G G H H G G G G G G G G G G G G P P P R s C s + + + + + + + =  +  +   = 例 2-14 系统的方块图如 2-35 所示，试画出信号流图，并用梅逊公式求系统的传递函数 ( ) ( ) R s C s