A first-order system G(s) = 5/(0.5s + 1) receives a step input of size 10 at t = 0, starting from rest. How long does the output take to reach 80 % of its final value? Find t.
Step response worksheet with answers
1.Easy
G(s) = 5/(0.5s + 1)U = 1080 %
t = s
2.Easy
A step is applied to a first-order process at t = 0. The output starts at 0 and settles at 10. At t = 1 s it reads 7. Find the time constant τ.
y(∞) = 10y(1) = 7
τ = s
3.Medium
A system has the transfer function G(s) = 108/(s² + 8s + 36) and receives a unit step input. Find the damping ratio ζ.
G(s) = 108/(s² + 8s + 36)
ζ =
4.Medium
A system has the transfer function G(s) = 7/(s² + 2s + 7) and receives a unit step input. The poles are s = σ ± jωd. Find the real part σ.
G(s) = 7/(s² + 2s + 7)
σ =
5.Hard
A second-order system without zeros must have a step response with 4.3 % overshoot. Find the damping ratio ζ.
%OS = 4.3 %
ζ =
6.Hard
A unity negative feedback loop has G(s) = 45/(s(s + 8)). Find the 2 % settling time ts of the closed-loop step response, using ts ≈ 4/(ζωₙ).
G(s) = 45/(s(s + 8))
ts = s
Answer key
- 1. t = 0.8047 s
- 2. τ = 0.8306 s
- 3. ζ = 0.6667
- 4. σ = −1
- 5. ζ = 0.7077
- 6. ts = 1 s
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