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All questions of Time response of discrete systems for Electrical Engineering (EE) Exam

Find the type and order of the system given below:
  • a)
    2,3
  • b)
    2,2
  • c)
    3,3
  • d)
    None of the mentioned
Correct answer is option 'B'. Can you explain this answer?

Nitya Chopra answered
Answer: Type = 2 which is the number of poles at the origin and order is the highest power of the characteristic equation.

The transfer function of the system is G(s) =100/(s+1) (s+100). For a unit step input to the system the approximate settling time for 2% criterion is:
  • a)
    100 sec
  • b)
    4 sec
  • c)
    1 sec
  • d)
    0.01 sec 
Correct answer is option 'B'. Can you explain this answer?

Mahesh Datta answered
Explanation: G(s) =100/(s+1) (s+100)
Taking the dominant pole consideration,
S=-100 pole is not taken.
G(s)= 100/s+1
Now it is first order system, ts=4T=4 sec.

Hence Answer (b) is correct

For complete preparation of Network Theory:

Normalized difference between the time response peak and steady state output is ______________
  • a) 
    Maximum peak overshoot
  • b) 
    Damping factor
  • c) 
    Minimum peak overshoot
  • d) 
    Undershoot
Correct answer is option 'A'. Can you explain this answer?

Devendra Kumar answered
As we know that, Graph of transient time where maximum peak is define as the difference between peak time and settling time.

since Peak time is defined as the maximum peak of the signal.

settling time is that where its become constant , there is no oscillation after settling.

A feedback control systems has the inherent capability that its parameter can be adjusted to alter both its transient and steady state responses.
  • a)
    True
  • b)
    False
Correct answer is option 'A'. Can you explain this answer?

Isha Singh answered
Answer: a
Explanation: Feedback’s inherent capability is that its parameter can be adjusted to alter both transient and steady state responses as together they are referred to as time responses.

 Time response during steady state the output velocity matches with the input velocity but lags behind the input by T.
  • a)
    True
  • b)
    False
Correct answer is option 'A'. Can you explain this answer?

Understanding Time Response in Steady State
In control systems, the time response describes how the output of a system responds to an input over time. When analyzing steady state conditions, it's essential to understand the behavior of the output in relation to the input.
Steady State Characteristics
- During steady state, the system has reached a balance where the output no longer changes with time.
- The output velocity corresponds to the input velocity, implying that the system effectively tracks the input.
Lagging Behavior
- Although the output matches the input in terms of magnitude, it does not do so instantaneously.
- The output is said to "lag" behind the input by a time constant, denoted as T.
- This lag is a result of the system's inherent dynamics, such as inertia and damping characteristics.
Conclusion
- Therefore, the statement that during steady state, the output velocity matches the input velocity but lags behind by T is indeed true.
- This behavior is crucial for system stability and performance in control applications, ensuring that the system can adapt to changes without overshooting or oscillating excessively.
Understanding this concept helps in designing and analyzing control systems in Electrical Engineering, ensuring they perform effectively in real-world applications.

It is generally used to analyze the transient response to one of the standard test signals.
  • a)
    Ture
  • b)
    False
Correct answer is option 'A'. Can you explain this answer?

Rahul Banerjee answered
Answer: a
Explanation: For analyzing transient response mainly step is used and also other signals mainly ramp and parabolic are not used for this analysis but they are used for steady state analysis.

The peak percentage overshoot of the closed loop system is :
  • a)
    5.0%
  • b)
    10.0%
  • c)
    16.3%
  • d)
    1.63%
Correct answer is option 'C'. Can you explain this answer?

Answer: c
Explanation: C(s)/R(s) = 1/s2+s+1
C(s)/R(s) = w/ws2+2Gws+w2
Compare both the equations,
w = 1 rad/sec
2Gw = 1
Mp = 16.3 %

Control system are normally designed to be:
  • a)
    Overdamped
  • b)
    Under damped
  • c)
    Un damped
  • d)
    Critically damped
Correct answer is option 'B'. Can you explain this answer?

Ayush Kumar answered
Answer: b
Explanation: Practically there are some non-linearity present in the system as friction but in mathematical model these are considered by considering high gain and lower damping.

Rise time, Peak time, maximum peak overshoot, settling time, and steady state error are mutually dependent.
  • a)
    True
  • b)
    False
Correct answer is option 'A'. Can you explain this answer?

Debanshi Nair answered
Answer: a
Explanation: Rise time, peak time, settling time and maximum peak overshoot are the prime factors of the time domain analysis and they must be specified in a consistent manner but they are mutually dependent.

The step response of the system is c(t) = 10+8e-t-4/8e-2t . The gain in time constant form of transfer function will be: 
  • a)
    -7
  • b)
    7
  • c)
    7.5
  • d)
    -7.5
Correct answer is option 'D'. Can you explain this answer?

Swara Dasgupta answered
Differentiating the equation and getting the impulse response and then taking the inverse Laplace transform and converting the form into time constant form we get K = -7.5.

Laplace transform of unit impulse signal is :
  • a)
    A/s
  • b)
    A
  • c)
    1
  • d)
    1/s
Correct answer is option 'C'. Can you explain this answer?

Mahi Bose answered
Answer: c
Explanation: Laplace response of impulse signal is one which implies Laplace response is systems response.

Standard test signals in control system are:
  • a)
    Impulse signal
  • b)
    Ramp signal
  • c)
    Unit step signal
  • d)
    All of the mentioned
Correct answer is option 'D'. Can you explain this answer?

Answer: d
Explanation: Standard test signals are impulse, ramp and unit step all of the above to test the dynamic behavior of the control system.

The output in response to a unit step input for a particular continuous control system is c(t)= 1-e-t. What is the delay time Td? 
  • a)
    0.36
  • b)
    0.18
  • c)
    0.693
  • d)
    0.289
Correct answer is option 'C'. Can you explain this answer?

Anirban Gupta answered
Answer: c
Explanation: The output is given as a function of time. The final value of the output is limn->∞c(t)=1; . Hence Td (at 50% of the final value) is the solution of 0.5=1-e-Td, and is equal to ln 2 or 0.693 sec.

The damping ratio and peak overshoot are measures of:
  • a)
    Relative stability
  • b)
    Speed of response
  • c)
    Steady state error
  • d)
    Absolute stability
Correct answer is option 'B'. Can you explain this answer?

Aman Jain answered
Answer: b
Explanation: Speed of response is the speed at which the response takes the final value and this is determined by damping factor which reduces the oscillations and peak overshoot as the peak is less then the speed of response will be more.

A system has a complex conjugate root pair of multiplicity two or more in its characteristic equation. The impulse response of the system will be:
  • a)
    A sinusoidal oscillation which decays exponentially; the system is therefore stable
  • b)
    A sinusoidal oscillation with a time multiplier ; the system is therefore unstable
  • c)
    A sinusoidal oscillation which rises exponentially ; the system is therefore unstable
  • d)
    A dc term harmonic oscillation the system therefore becomes limiting stable
Correct answer is option 'C'. Can you explain this answer?

The impulse response of a system can provide valuable information about its behavior and stability. In this case, we are given that the system has a complex conjugate root pair of multiplicity two or more in its characteristic equation. Let's analyze the implications of this on the system's impulse response.

Complex Conjugate Root Pair
A complex conjugate root pair in the characteristic equation of a system indicates the presence of oscillatory behavior in the system's response. Complex conjugate roots are of the form a ± bi, where a and b are real numbers and i is the imaginary unit (√-1). These roots give rise to sinusoidal terms in the impulse response.

Multiplicity Two or More
The multiplicity of a root refers to the number of times it appears in the characteristic equation. When a complex conjugate root has a multiplicity of two or more, it means that it appears multiple times in the equation. This results in an exponential rise or decay in the sinusoidal terms of the impulse response.

Implications on the Impulse Response
Based on the given information, the impulse response of the system will exhibit the following characteristics:

1. Sinusoidal Oscillation: The presence of a complex conjugate root pair indicates the occurrence of sinusoidal terms in the impulse response. These sinusoids represent the oscillatory behavior of the system.

2. Exponential Rise: Since the complex conjugate root pair has a multiplicity of two or more, the sinusoidal terms in the impulse response will experience exponential rise. This means that the amplitude of the oscillation will increase over time.

3. Unstable System: An exponentially rising sinusoidal term indicates an unstable system. As the amplitude continuously grows, the system's response becomes unbounded and uncontrollable. This behavior is undesirable in most engineering applications.

Conclusion
In summary, a system with a complex conjugate root pair of multiplicity two or more in its characteristic equation will have an impulse response that exhibits a sinusoidal oscillation with exponential rise. This behavior indicates an unstable system, as the response grows without bound.

The peak percentage overshoot of the closed loop system is :
  • a)
    5.0%
  • b)
    10.0%
  • c)
    16.3%
  • d)
    1.63%
Correct answer is option 'C'. Can you explain this answer?

Nitin Chawla answered
Answer: c
Explanation: C(s)/R(s) = 1/s2+s+1
C(s)/R(s) = w/ws2+2Gws+w2
Compare both the equations,
w = 1 rad/sec
2Gw = 1
Mp = 16.3 %

Consider the input with the inputs 4 u(t) and the impulse response 5 +7 , the time constants of the output are,
  • a)
    0.2, 0.33 and 0.5
  • b)
    4.5 and 7
  • c)
    0.2, 0.4 and 0.7
  • d)
    0.2, 0.1 and 0.25
Correct answer is option 'A'. Can you explain this answer?

Shivam Sharma answered
Output response so calculated is the inverse Laplace transform of the input and impulse response and hence converting the resultant form in the time constant form time constant can be directly determined.CORRECT OPTION IS (A).

Find the initial and final values of the following function:
F(s) = 12(s+1)/s(s+2)^2(s+3)
  • a)
    1,∞
  • b)
    0,∞
  • c)
    ∞,1
  • d)
    0,1
Correct answer is option 'D'. Can you explain this answer?

Ameya Nambiar answered
Answer: d
Explanation: Using final and initial values theorem directly to find initial and final values but keeping in mind that final value theorem is applicable for stable systems only.

The transfer function of a system is G(s) = 100/(s+1) (s+100). For a unit step input to the system the approximate settling time for 2% criterion is:
  • a)
    100 sec
  • b)
    4 sec
  • c)
    1 sec
  • d)
    0.01 sec
Correct answer is option 'B'. Can you explain this answer?

Rounak Rane answered
Answer: b
Explanation: Comparing the equation with the characteristic equation and then finding the value of G and w and calculating the value of settling time as 4 sec from 4/Gw.

Let c(t) be the unit step response of a system with transfer function K(s+a)/(s+K). If c(0+) = 2 and c(∞) = 10, then the values of a and K are respectively.
  • a)
    2 and 10
  • b)
    -2 and 10
  • c)
    10 and 2
  • d)
    2 and -10
Correct answer is option 'C'. Can you explain this answer?

Ayush Kumar answered
Answer: c
Explanation: Applying initial value theorem which state that the initial value of the system is at time t =0 and this is used to find the value of K and final value theorem to find the value of a.

Transient response analysis is done for_________ systems.
  • a)
    Unstable
  • b)
    Stable
  • c)
    Conditionally stable
  • d)
    Marginally stable
Correct answer is option 'B'. Can you explain this answer?

Sagarika Patel answered
Transient response analysis is the most general method for computing forced dynamic response. The purpose of a transient response analysis is to determine the behavior of a structure subjected to time-varying excitation. The transient excitation is explicitly defined in the time domain.

Which of the following transfer function will have the greatest maximum overshoot? 
  • a)
    9/(s2+2s+9)
  • b)
    16/(s2+2s+16)
  • c)
    25/(s2+2s+25)
  • d)
    36/(s2+2s+36)
Correct answer is option 'D'. Can you explain this answer?

Disha Das answered
Answer: d
Explanation: Comparing the characteristic equation with the standard equation the value of the damping factor is calculated and the value for the option d is minimum hence the system will have the maximum overshoot .

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