[SciPy-User] Wrong Step Response

otti otti@gargamels-haus....
Wed May 23 03:01:31 CDT 2012

Hello everyone,

after reading some threads about step response problems in the mailing list
i couldnt come up with a proper solution for my problem.

I've got the following transfer function:

G = Vr/(sT1*(1+sT2))

Vr = 2/15
T1 = 0.2
T2 = 1

For this i like to plot the step response so i made the following script:

*---Begin Script*

# some imports
import numpy as np
import matplotlib.pyplot as plt
import scipy as sp
from scipy import signal

# Constants
T1 = 0.2
T2 = 1
Vr = float(2)/15
Tsim = 50

# Denumerator
N0 = np.array([T1*T2 ,T1 , 0])

# numerator
Z0 = Vr

# create tfcn
sys = sp.signal.lti(Z0, N0)

# create the step response
t = np.linspace(0, Tsim, 1000)
u = np.arange(len(t))
u = np.ones_like(u)
yout = sp.signal.lsim2(sys, T=t, U=u)[1]

plt.plot(t, u, t, yout/yout.max())

*---End Script*

This gives me the following response, which i know is not the rigth one 
because i made this one
already in a lab at university with MATLAB but i don't have MATLAB at 
home because i prefer to use Numpy+Scipy+Matplotlib.

wrong step response

Here is the correct response:

correct step response

After several hours of reading an trying different approaches im kind of 
frustrated ^^.

I would be really thankfull for any help so that i can keep on going the 
Scipy track.

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