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Replies: 2   Last Post: Dec 12, 2012 3:18 AM

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 justlooking for someone else Posts: 77 Registered: 12/10/04
Posted: Dec 12, 2012 3:18 AM

Sorry, the closed loop transfer function's steady state error is:

abs(1-dcgain(sys))

If using an openloop transfer function, the function must first be closed
abs(1-dcgain(feedback(sys,1))) % for unity feedback

Alternatively if using an openloop transfer function with unity feedback, then the steady state step error is
1/(1+dcgain(sys))

where dcgain(sys) is the static error constant Kp

"A" wrote in message <ka9drm\$n60\$1@newscl01ah.mathworks.com>...
> The previous response to this is not correct. The steady state error can be calculated in two ways depending on the type of transfer function:
>
> abs(dcgain(sys)-1)
> for a closed loop transfer function
>
>
>
> Jon Carter <jdc298REMOVE-THIS@soton.ac.uk> wrote in message <38E0D27C.619EB741@soton.ac.uk>...

> > Hi
> >
> > I'm looking to calculate the steady state error of a transfer function
> > with a unit step input in Matlab. I can do this by using step() to draw
> > a plot of the response, but is there a function that would tell me the
> > error without needing to read it off graphically?
> >
> > Thanks,
> >
> > --
> > Jon
> > jdc298REMOVE-THIS@soton.ac.uk

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