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++2G₁C(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 = 2. Find the overall gain T = C/R.

G₁ = 2G₂ = 11G₃ = 1signs: + G₂, + G₃
T =
2.Easy
R(s)+7s + 8G(s)C(s)−

A plant G(s) = 7/(s + 8) is placed in a unity negative feedback loop. Find the closed-loop pole p.

G(s) = 7/(s + 8)unity negative feedback
p =
3.Medium
R(s)+32s + 7G(s)C(s)0.5H−

A plant G(s) = 32/(s + 7) is controlled in a negative feedback loop whose sensor has the gain H = 0.5. Find the time constant τ of the closed loop.

G(s) = 32/(s + 7)H = 0.5
τ = s
4.Medium
R(s)+Ks(s + 8)G(s)C(s)−

The plant G(s) = K/(s(s + 8)) 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(s + 8))unity negative feedback
K =
5.Hard
R(s)+Kcontroller+D(s)+5s + 4plantC(s)−

A proportional controller K drives the plant G(s) = 5/(s + 4) in a unity negative feedback loop. A disturbance step of size 10 enters at the plant input while R = 0. Find the smallest gain K that keeps the steady-state output at or below 0.625.

G(s) = 5/(s + 4)D = 10css ≤ 0.625
K =
6.Hard
R(s)+K(s + 5)(s + 6)(s + 8)G(s)C(s)−

The plant G(s) = K/((s + 5)(s + 6)(s + 8)) is in a unity negative feedback loop. At the largest stable gain the loop oscillates. Find the frequency of oscillation ω in rad/s.

G(s) = K/((s + 5)(s + 6)(s + 8))unity negative feedback
ω = rad/s

Answer key

  1. 1. T = 24
  2. 2. p = −15
  3. 3. τ = 0.04348 s
  4. 4. K = 16
  5. 5. K = 15.2
  6. 6. ω = 10.86 rad/s

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