JNTU B.Tech II CONTROL THEORY Previous Question Paper (November/December - 2020 - R16)

An open-loop control system is one in which the control action is independent of the output. It is simple, inexpensive, and stable, but it is highly sensitive to external disturbances and parameter variations, and it cannot automatically correct for errors. In contrast, a closed-loop control system (feedback system) compares the output with the reference input and adjusts the control action to minimize the error. While more complex, expensive, and potentially unstable, closed-loop systems offer higher accuracy, reduced sensitivity to disturbances, and improved transient response characteristics.

Since the specific block diagram image was not provided, the general procedure to determine the transfer function C(s)/R(s) is as follows:

1. Identify and eliminate all minor feedback loops using the standard formula: G(s) / (1 ± G(s)H(s)).
2. Shift take-off points and summing points as necessary to simplify the topology, ensuring that the equivalent transfer function is maintained.
3. Combine blocks in series by multiplying their transfer functions and blocks in parallel by adding them algebraically.
4. Continue the reduction process until the system is represented by a single forward path block G'(s) and a single feedback path H'(s).
5. Apply the closed-loop transfer function formula: C(s)/R(s) = G'(s) / (1 + G'(s)H'(s)) for negative feedback, or C(s)/R(s) = G'(s) / (1 - G'(s)H'(s)) for positive feedback.