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)15G₂2G₃++6G₁C(s)

The signal R splits into two parallel blocks G₂ = 15 and G₃ = 2. 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 = 15G₃ = 2signs: + G₂, + G₃
T =
2.Easy
R(s)+10GC(s)0.02H+

An amplifier with gain G = 10 has positive feedback through a path with gain H = 0.02 (the feedback signal is added at the summing junction). Find the closed-loop gain T = C/R.

G = 10H = 0.02positive feedback
T =
3.Medium
R(s)+18s + 6G(s)C(s)0.25H−

A plant G(s) = 18/(s + 6) is controlled in a negative feedback loop whose sensor has the gain H = 0.25. Find the time constant τ of the closed loop.

G(s) = 18/(s + 6)H = 0.25
τ = s
4.Medium
R(s)+6K+2s + 4G(s)C(s)1H₁−−

The plant G(s) = 2/(s + 4) has an inner (minor) negative feedback loop with gain H₁ = 1. A controller gain K = 6 and an outer unity negative feedback loop close the system. Find the closed-loop pole p.

G(s) = 2/(s + 4)H₁ = 1K = 6
p =
5.Hard
R(s)+Ks(s + 3)(s + 4)G(s)C(s)−

The plant G(s) = K/(s(s + 3)(s + 4)) 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(s + 3)(s + 4))unity negative feedback
ω = rad/s
6.Hard
R(s)+20s(s + 3)G(s)C(s)1H−

The plant G(s) = 20/(s(s + 3)) is in a negative feedback loop with sensor gain H = 1. The closed-loop poles are complex. Find their real part σ.

G(s) = 20/(s(s + 3))H = 1
σ =

Answer key

  1. 1. T = 102
  2. 2. T = 12.5
  3. 3. τ = 0.09524 s
  4. 4. p = −18
  5. 5. ω = 3.464 rad/s
  6. 6. σ = −1.5

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