A step is applied to a first-order process at t = 0. The output starts at 0 and settles at 10. At t = 2 s it reads 4. Find the time constant τ.
Step response worksheet with answers
1.Easy
y(∞) = 10y(2) = 4
τ = s
2.Easy
A first-order system G(s) = 15/(s + 5) receives a step input of size 10 at t = 0, starting from rest. Find the final value y(∞) of the output.
G(s) = 15/(s + 5)U = 10
y(∞) =
3.Medium
A system has the transfer function G(s) = 47.5/(s² + 15s + 95) and receives a unit step input. The poles are s = σ ± jωd. Find the real part σ.
G(s) = 47.5/(s² + 15s + 95)
σ =
4.Medium
A system has the transfer function G(s) = 20/(s² + 4s + 40) and receives a unit step input. Find the damping ratio ζ.
G(s) = 20/(s² + 4s + 40)
ζ =
5.Hard
A second-order system without zeros must have a step response with 5 % overshoot. Find the damping ratio ζ.
%OS = 5 %
ζ =
6.Hard
A unity negative feedback loop has G(s) = 145/(s(s + 8)). Find the 2 % settling time ts of the closed-loop step response, using ts ≈ 4/(ζωₙ).
G(s) = 145/(s(s + 8))
ts = s
Answer key
- 1. τ = 3.915 s
- 2. y(∞) = 30
- 3. σ = −7.5
- 4. ζ = 0.3162
- 5. ζ = 0.6901
- 6. ts = 1 s
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