JNTU
JNTU B.Tech III CONTROL SYSTEMS Previous Question Paper (July/August - 2023 - R13)
Note: i) Question paper consists of Part A, Part B. ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions. iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
Part A
Discuss about open loop system with an example.
Answer
An open loop control system is a system in which the control action is independent of the output of the system. In these systems, the output has no effect on the input signal, meaning there is no feedback mechanism to compare the actual output with the desired reference input.
A common example is an electric toaster. The duration of the toasting process is set by a timer, regardless of the actual browning level or temperature of the bread. Since the device does not measure the output (the state of the bread) to adjust its operation, it functions as an open loop system.
Explain how feedback effects Sensitivity of the system.
Answer
Feedback significantly reduces the sensitivity of a control system to variations in internal parameters. Sensitivity is defined as the ratio of the percentage change in the overall transfer function to the percentage change in a specific parameter.
For an open-loop system with transfer function G(s), the sensitivity to changes in G is 1. When negative feedback with a gain H(s) is introduced, the closed-loop transfer function becomes T(s) = G / (1 + GH). The sensitivity of T with respect to G is given by:
Since the term (1 + GH), known as the return difference, is typically much greater than 1 in a well-designed feedback system, the sensitivity is reduced by a factor of (1 + GH). This makes the system output more robust and less dependent on fluctuations in component values or environmental changes.
What is Synchro?
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Draw the block diagram of the second order system.
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Define steady state response and steady state error.
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What does the term ‘type’ of a system indicate? What is its significance?
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What conclusion can be made if there is a row of all zeros in the Routh array?
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Explain the effect of adding zero to G(s)H(s) on the root loci.
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What is Gain cross over frequency and explain it in detail.
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What are frequency domain specifications?
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Part B
Find the impulse response of the system described by G(s)H(s) = 1 / (s^2 + 6s + 8).
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What is the classification of control systems and discuss the importance of mathematical modelling of a control system.
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State essential differences by giving suitable examples and highlight their merits and demerits for open loop and closed loop systems.
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For the geared system shown in Figure 1, find the transfer function relating the angular displacement θL to the input torque T1.
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List the properties of signal flow graphs.
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Obtain the transfer function using block diagram reduction technique (Figure 2).
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Derive an expression for the transfer function of an armature-controlled DC servo motor.
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The open-loop transfer function of unity feedback system is G(s) = 4 / (s(s+1)). Determine the nature of the closed-loop system for a unit-step input. Also determine rise time, peak time, and peak overshoot.
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Obtain the time response of a first order system for a unit step input and plot its response.
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Explain the effect of PD and PI controllers on the system response.
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Explain the Routh’s criteria with an example.
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A system has G(s)H(s) = K / ((s+2)(s+4)(s+8)), where K is positive. Determine the range of K for stability.
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Sketch the root locus of the system G(s)H(s) = K(s+3) / (s(s+6)(s^2+2s+2)).
Find marginal value of K.
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Find the value of K for damping ratio of 0.5.
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Explain the general procedure for constructing Bode plots.
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Draw Bode plots for the given unity feedback control system and determine gain margin and phase margin.
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Sketch the bode plots and determine the gain cross-over and phase cross-over frequencies for the given transfer function.
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