Im not sure of your knowledge level, so I'm going to dump quite a bit of information out without really answering your question directly.i need help, which is why i am posting.
I can only get up to:
40k / s^3 + 3s^2 + + 15s + 40k
Yes, it is different, but it's good that you do understand 2'nd order systems. Otherwise, it would be too difficult to understand this system or any other higher order systems. Is the information I provided in any way useful? Do you see the value in representing your 3'rd order system as the concatenation (i.e. multiplication of transfer functions) of a first order system with a second order system? Do you understand how to determine that your system contains a second order underdamped systems?I do understand second order system but as this is a third it is different.
Referring to the feedback that you show in the figure, - is it positive or negative feedback? The diagram shows a summing node with no indication of positive or negative signs. This usually means all inputs are added, but your total transfer function is only correct if the feed back is negative.the open loop transfer function is attached.
which orginal post are you refering to? that was the question i was given.If you take a look at the material at this link you should be able to spot the flaw in your interpretation of the expression for the transfer function in your original post.
hgmjr
OK, makes sense now. Your first post is the open loop transfer function and then later you give the closed loop transfer function with negative feedback.yes steveb it is useful. thanks
which orginal post are you refering to? that was the question i was given.
As for the negative or positive. the postive sign is on at the top and negative on the lower.
thanks for your keep responses guys
Above is the original post that started this thread. The formula it contains is the one to which I was referring.40K / s(s+3)(s+5)
How do i find the damping ratio and also the gain...K?
thanks
It would help to know exactly what the issue is. Otherwise we will just be guessing and not helping you in the area that is giving you trouble.I still am having trouble in working out the expression
The expression you have given for the closed-loop transfer function is correct. I would however recommend that you proceed and multiply the s-terms in the denominator.ok, yes im farmilair with quadratic equation.
I have to use both matlab and hand calculations for it.
I have to firstly find the gain K, given steadystate error 0.15. I guess with the K value i can easily plot the root locus but i need to find K which is what i am asking.
From the root locus i need to find the undamped namtural freq, damping ratio and settling time.
I then need to find the K to get a damping ratio of 0.5.
the problem arises when we have not really been taught matlab so it is exceptionally hard for me. I know a little but not enough to derive what i need.
You have the diagram which is part of the question.
i forgot to add can use matlab to get the root locus.
So i need to find K to insert it into matlab. Then i cant get the root locus and work out the rest. So my question is how do i get the gain value K from 40K / s(s+3)(s+5).
and i would like to know if my first step is correct.
40K / s(s+3)(s+5)+40K
thank you
You have many steps, so let's go one at a time.I have to firstly find the gain K, given steadystate error 0.15. I guess with the K value i can easily plot the root locus but i need to find K which is what i am asking.
I'm having trouble understanding this specification. I don't know what unit velocity means.what we are given is steady state input error to unit velocity = 0.15