A step is applied to a first-order process at t = 0. The output starts at 0 and settles at 20. At t = 2 s it reads 12. Find the time constant τ.
Step response worksheet with answers
1.Easy
y(∞) = 20y(2) = 12
τ = s
2.Easy
A first-order system G(s) = 0.5/(2s + 1) receives a step input of size 20 at t = 0, starting from rest. Find the output y(1) at t = 1 s.
G(s) = 0.5/(2s + 1)U = 20t = 1 s
y(1) =
3.Medium
A system has the transfer function G(s) = 34/(s² + 5s + 34) and receives a unit step input. Find the percent overshoot %OS of the step response.
G(s) = 34/(s² + 5s + 34)
%OS = %
4.Medium
A system has the transfer function G(s) = 44.5/(s² + 9s + 89) and receives a unit step input. Find the percent overshoot %OS of the step response.
G(s) = 44.5/(s² + 9s + 89)
%OS = %
5.Hard
A unity negative feedback loop has G(s) = 125/(s(s + 6)). Find the 2 % settling time ts of the closed-loop step response, using ts ≈ 4/(ζωₙ).
G(s) = 125/(s(s + 6))
ts = s
6.Hard
A second-order system without zeros must have a step response with 8 % overshoot. Find the damping ratio ζ.
%OS = 8 %
ζ =
Answer key
- 1. τ = 2.183 s
- 2. y(1) = 3.935
- 3. %OS = 22.52 %
- 4. %OS = 18.18 %
- 5. ts = 1.333 s
- 6. ζ = 0.6266
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