# Electronics and Communication Engineering - Automatic Control Systems - Discussion

20.

A system has its two poles on the negative real axis and one pair of poles lies on jω axis. The system is

 [A]. stable [B]. unstable [C]. limitedly stable [D]. either (a) or (c)

Explanation:

Poles on j x-axis lead to oscillations.

 Amit Khambad said: (Feb 20, 2015) How explain?

 Anish Kumar said: (May 27, 2015) Limitedly stable. When it lies on left of jw axis then it is known as unstable. When it lies on right of jw axis then it is known as stable. When it lies on jw axis then it is known as limitedly stable.

 Rc Kashyap said: (Mar 22, 2016) When it lies on left of jw axis then it is known as stable. When it lies on right of jw axis then it is known as unstable. When it lies on jw axis then it is known as limitedly stable or marginally stable.

 Jit said: (Feb 8, 2017) But if poles are repeated on jw axis then the system is unstable, right?

 Kishor Kumar said: (Nov 14, 2018) I think it will be limited stable if it has two poles only lies on JW-axis and have no real poles lies on negative real axis, now if it exists (poles on negative real axis) then it will be underdamped oscillation which is the stable case.