why am i not getting same matlab results when doing manually?

lukus09

i want to find rise time, peak time, maximum overshoot and settling time to 2% of the final value for 12/ s^2 + 5s +11 manually.

however when i calcualte the results manually they are different to the matlab results. I know the equations are correct becuase i got them off a book, and have thorughly gone through each equation again to ensure it is correct. Im only getting the maximum overshoot value correct. The rise time and settling time are quite close to matlab results but not exact as they should be because i am rounding to 5 DP!!!

mertesn

Based on what I'm seeing here (and I have no matlab experience) I would suggest some parentheses. I am assuming your formula would look like this on paper:

12

---

s^2 + 5s + 11

What you have written would be interpreted by the computer like this:
(12 / s^2) + 5s + 11.

What you want would look more like this:
12 / (s^2 + 5s + 11)

Hope this helps.

lukus09

sorry its 11 not 12.
but matlab interprets it as a transfe function so it reads it as 12 / s^2 + 5s + 12.

mertesn wrote:

Based on what I'm seeing here (and I have no matlab experience) I would suggest some parentheses. I am assuming your formula would look like this on paper:

12

---

s^2 + 5s + 11

What you have written would be interpreted by the computer like this:
(12 / s^2) + 5s + 11.

What you want would look more like this:
12 / (s^2 + 5s + 11)

Hope this helps.

shwaip

post your code or we have no idea what you're doing wrong.