SHORT ANSWERS

UNIT-1
1. What are the effects of feedback on the performance of a system? Briefly explain.

A. Feedback in a system significantly impacts its performance by affecting aspects like stability,
accuracy, sensitivity, and disturbance rejection

2. What are the differences between open loop and closed loop control systems?

A. Open loop systems lack feedback, meaning they operate independently of the actual output,
while closed loop systems utilize feedback to adjust the input based on the system's output

3. Explain a closed loop control system with its components

A. Closed loop control system uses feedback to automatically regulate a system to achieve a desired
outcome. Components:plant,feedback path element,error detector and controller

4. Write the advantages and disadvantages of open and closed loop systems.

A. Open loop systems are simpler and cheaper but less accurate and adaptable. Closed loop systems
are more complex and expensive but offer higher accuracy and can handle disturbances.

5. What are the characteristics of servomotors?

A. 1.linear relationship between speed and electric control signal

2.steady state stability

3.wide range of speed control

4.low mechanical and electrical inertia

5.fast response

6. What is synchro?

A. A synchro is an electromagnetic transducer commonly used to convert an angular position of a

7. What are the applications of synchros?

A. Synchros are used in servomechanism as error detector and to convert angular displacement to
proportional electrical signal

8. Define the term 'Impulse response of a system'.

A. The impulse response of a system is defined as the output when the input is a unit impulse
function s(t). Once the impulse response of a linear system is known, the output of the system c(t),
with any input r(t) can be found by using the transfer function.

9. How is the transfer function to be derived when a number of systems are cascaded?

A. When loading is considered, the overall transfer function should be derived ived by basic analysis
without regard to individual transfer functions.
10. Name the analogous electrical elements in force-voltage analogy for the elements of mechanical
translational system?

A. In force-voltage analogy, the analogous quantities in mechanical translational and electrical

UNIT-2
1.Explain the differences AC servomotor and DC servo motor.

2. What do you mean by loop gain?

A. The product of branch gains encouraged in traversing a loop is called the loop gain

3. What do you mean by a signal flow graph?

A. A signal flow graph is a graphical representation of the relationships between the variables of a
set of linear algebraic equations written in the form of cause-and-effect relations

4. compare block diagram and signal flow graph method

5. What do you mean by steady-state response? On what does it depend?

A. The steady-state response of a system is that part of the time response which remains constant as
t→∞. It is dependent on the system poles as well as on the type of the input

6. What is the importance of test signals?

A. *The test signals are used to pre-determined the performance of the system

*The test signals can be easily generated in laboratories and characteristics of test signals
resembles the characteristics of actual signals

7. Define the terms:

(b) Zero

A. The pole of a function F(s) is the value of s for which the function F(s) becomes infinite. The zero
of a function F(s) is the value of s for which the function F(s) becomes zero

8. Define the characteristics equation

A.The denominator of the closed loop transfer function equated to zero is called the characteristics
equation.

9. Define the term 'damping ratio' of a system.

A. The damping ratio of a system is defined as the ratio of actual damping to critical damping

10. What does the time constant of a system indicate?

A. The time constant of a system is indicative of how fast the system tends to reach the final value. A
large time constant corresponds to a sluggish system and a small time constant corresponds to fast
response

UNIT-3
1. What does the presence of negative terms during the formulation of the Routh array mean?

A. The presence of negative terms during the formulation of the Routh array means that the
characteristic equation has one or more roots in the right-half of the s-plane and hence the system is
unstable.
6. What are the applications of the root locus?

A. The applications of the root locus are:

* The root locus can be used to solve higher-order algebraic equations.

* It can be used to determine the absolute stability as well as the relative stability of a system.

* The value of open-loop gain K for any root location can be obtained from the root locus.

* It can be used for the design of control systems.

* It gives information about the transient response of a system.

7. What are the advantages of the root locus?

A. The advantages of the root locus are as follows:

* It can be used to determine the absolute stability as well as the relative stability of control
systems.

* It is a time-domain technique.

* The transient response of a system can be determined from its root locus.

* Higher-order algebraic equations can be solved using the root locus.

* It provides a measure of sensitivity of roots to the variation in the parameter being considered.

* It can be used for design and compensation of control systems.

9. What do you mean by the break angle? How is it determined?

A. The break angle is the angle at which the root locus branches travel immediately after breaking
away

10. What are dominant poles?

A. The dominant poles are the poles which are very near to the origin. They dominate or decide the
transient response of a higher-order system

UNIT-4
1. What is the Bode plot?

A. The Bode plot also called the logarithmic plot, is a frequency response plot of the transfer
function of a system. It consists of two plots: magnitude plot and phase plot. The magnitude plot is a
graph between the magnitude of G(jw)H(jw) expressed in dB and the frequency won the log scale.
The phase plot is a graph between the phase angle of G(jw)H(jw) in degrees and the frequency w on
the log scale.

2. What is the advantage of polar plots?

A. An approximate polar plot can be drawn quickly and polar plots can be used for stability studies of
control systems

3. Define corner frequency.

A. The magnitude Bode plot can be approximated by straight line asymptotes. The frequency at
which the low frequency and high frequency asymptotes meet is called the corner frequency. The
slope of the magnitude plot changes at the corner frequencies

4. Define the gain crossover frequency.

A. The gain crossover frequency is defined as the frequency at which the resultant magnitude is zero
dB, i.e., the gain crossover frequency is defined as the frequency at which |G(jw)H(jw)| = 1.

5. Define the phase crossover frequency

A. The phase crossover frequency is defined as the frequency at which the resultant phase is -180°
i.e. the phase crossover frequency is defined as the frequency at which ⟨G(j)H(j) = -180°.

6. How do you determine the gain crossover frequency @ and phase crossover frequency from the
Bode plot?

A. To determine the gain crossover frequency and phase crossover frequency from the Bode plots,
first draw the magnitude and phase Bode plots. Locate the frequency at which the resultant
magnitude plot crosses the zero dB line. This gives the gain cross-over frequency.

Locate the frequency at which the resultant phase plot crosses the -180° line. This gives the phase
crossover frequency

7. What is the drawback of the Nyquist stability criterion?

A. The drawback of the Nyquist stability criterion is that unlike the root locus method, the Nyquist
criterion does not give the exact location of the characteristic equation roots

8. What is the effect of addition of a zero to G(s)H(s) on the Nyquist plot?

A. The effect of addition of a zero to the loop transfer function is to rotate the high frequency
portion of the Nyquist plot by 90° in the counterclockwise direction without affecting the value at w
= 0. So, it has the affect of reducing the overshoot and the general affect of stabilization

9. What are constant N circles?

A. Let N = tan a, where a is the phase of the closed-loop transfer function with unity feedback. For
each constant value of N, a circle can be drawn in the complex plane. The family of these circles is
called N circles.

10. What is the advantage of constant M and N circles?

A. The advantage of constant M and N circles is that the closed-loop frequency response
specifications can be determined directly from the open-loop frequency response using M and N
circles.
UNIT-5
1. What are compensators?

A. Compensators are corrective sub-systems used to compensate for the deficiency in the
performance of the plant

4. What are the advantages of frequency-domain methods of compensation?

A. The advantages of frequency-domain methods of compensation are: (i) simplicity in analysis and
design and (ii) ease in experimental determination of frequency response for real systems.

5. In the state-model with usual notation, what are x(t), u(t), y(t), A, B, C, D and what are their
dimensions?

A. In the state model, x(t) is an n x 1 state vector, u(t) is an m x 1 input vector, y(t) is a p x 1 output
vector, A is an n x n system matrix, B is an n x m input matrix, C is a p x n output matrix, and D is a p x
m transmission matrix.

6. What are the effects and limitations of phase-lag control?

A.

* The gain crossover frequency is decreased and thus the bandwidth of the system is reduced

* The rise and settling times of the system are usually longer, since the bandwidth is usually
decreased

* The system is more sensitive to parameter changes, with a sensitivity function greater than one for
frequencies above its bandwidth

* The addition of attenuation of high frequencies improves the signal to noise ratio of the system
7. Explain State space

A. State-space: The n dimensional space whose coordinate axes consists of the x₁ axis, x2 axis,...,x,
axis where x₁, x2, ..., xn, are state variables is called a state-space.

8.What do you mean by a (a) homogeneous state equation ( tion?

A. (a) A homogeneous state equation is one in which the forcing function is zero.

( b) A nonhomogeneous state equation is one in which the forcing function is present

9.

10. What is the necessary and sufficient condition for output controllability of the system?

A. The necessary and sufficient condition for output controllability of a system is that the rank of the
matrix [CB CAB... CAn-1B D] should be m