Block diagrams worksheet with answers

Free printable Block diagrams worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy
R(s)11G₂1G₃+−6G₁C(s)

The signal R splits into two parallel blocks G₂ = 11 and G₃ = 1. Their outputs meet at a summing junction with the signs shown (+ and −), and the sum passes through G₁ = 6. Find the overall gain T = C/R.

G₁ = 6G₂ = 11G₃ = 1signs: + G₂, − G₃
T =
2.Easy
R(s)9G₂6G₃++10G₁C(s)

The signal R splits into two parallel blocks G₂ = 9 and G₃ = 6. Their outputs meet at a summing junction with the signs shown (+ and +), and the sum passes through G₁ = 10. Find the overall gain T = C/R.

G₁ = 10G₂ = 9G₃ = 6signs: + G₂, + G₃
T =
3.Medium
R(s)+5K+4s + 6G(s)C(s)1H₁−−

The plant G(s) = 4/(s + 6) has an inner (minor) negative feedback loop with gain H₁ = 1. A controller gain K = 5 and an outer unity negative feedback loop close the system. Find the closed-loop pole p.

G(s) = 4/(s + 6)H₁ = 1K = 5
p =
4.Medium
R(s)+K(s + 3)(s + 9)G(s)C(s)−

The plant G(s) = K/((s + 3)(s + 9)) is in a unity negative feedback loop. Find the gain K for which the closed loop is critically damped (two equal real poles).

G(s) = K/((s + 3)(s + 9))unity negative feedback
K =
5.Hard
R(s)+Kcontroller+D(s)+1s + 10plantC(s)−

A proportional controller K drives the plant G(s) = 1/(s + 10) in a unity negative feedback loop. A disturbance step of size 1 enters at the plant input while R = 0. Find the smallest gain K that keeps the steady-state output at or below 0.01.

G(s) = 1/(s + 10)D = 1css ≤ 0.01
K =
6.Hard
R(s)+5s + 1G₁+1s + 8G₂C(s)0.5H₁−0.25H₂−

Reduce the block diagram with G₁ = 5/(s + 1), G₂ = 1/(s + 8), an inner negative feedback H₁ = 0.5 around G₂ and an outer negative feedback H₂ = 0.25. Find the DC gain T(0) of C(s)/R(s).

G₁ = 5/(s + 1)G₂ = 1/(s + 8)H₁ = 0.5H₂ = 0.25
T(0) =

Answer key

  1. 1. T = 60
  2. 2. T = 150
  3. 3. p = −30
  4. 4. K = 9
  5. 5. K = 90
  6. 6. T(0) = 0.5128

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