JNTU B.Tech II CONTROL SYSTEMS Previous Question Paper (July/August - 2021 - R16)

An open-loop control system is one in which the control action is independent of the output. It does not have feedback, making it simple to construct and inexpensive, but it is sensitive to external disturbances and parameter variations, and its accuracy depends on calibration.

A closed-loop control system, or feedback control system, is one in which the control action depends on the output. It uses a feedback path to compare the actual output with the desired input (reference), generating an error signal that the controller uses to minimize the difference. While more complex, expensive, and potentially prone to instability, closed-loop systems are highly accurate, robust against disturbances, and less sensitive to non-linearities.

To find the transfer function Y(s)/R(s) for a block diagram, apply Mason's Gain Formula: T(s) = Σ Pk Δk / Δ.

1. Identify all forward paths (Pk) from the input R(s) to the output Y(s).
2. Identify all individual feedback loops and their gains.
3. Calculate the determinant Δ = 1 - (sum of all individual loop gains) + (sum of gains of all non-touching loop pairs) - (sum of gains of all non-touching loop triplets) + ...
4. Determine Δk for each forward path, which is the value of Δ for the part of the system not touching the kth forward path.
5. Substitute these values into the formula to obtain the overall transfer function.

The final result is obtained by simplifying the algebraic expression resulting from the ratio of the forward path gains adjusted by their respective determinants to the system determinant.