82 + Interview Questions in Digital Control Systems in Control Systems Page 1 InterviewSolution

1.	Phase margin is always positive for stable feedback system?(a) True(b) FalseI had been asked this question in a job interview.The doubt is from Compensation Techniques topic in section Digital Control Systems of Control Systems
Answer» The CORRECT CHOICE is (a) True The EXPLANATION is: Phase margin is calculated at the gain cross over frequency at which the gain is 1 and this is calculated for stability and is always positive for STABLE feedback system.

Discussion

2.	The given characteristic equation s^4+s^3+2s^2+2s+3=0has:(a) Zero root in the s-plane(b) One root in the RHS of s-plane(c) Two root in the RHS of s-plane(d) Three root in the RHS of s-planeThis question was posed to me in quiz.Question is from Stability Analysis in division Digital Control Systems of Control Systems
Answer» The CORRECT answer is (c) Two root in the RHS of s-plane Best EXPLANATION: The stability analysis is done USING Routh-Hurwitz criterion and hence the number of roots on the right is calculated.

Discussion

3.	The DFT of a signal x(n) of length N is X(k). When X(k) is given and x(n) is computed from it, the length of x(n)(a) Is increased to infinity(b) Remains N(c) Becomes 2N – 1(d) Becomes N2The question was asked during an interview.The query is from The Z-transform Analysis of Sampled-Data Control Systems in section Digital Control Systems of Control Systems
Answer» Right choice is (a) Is increased to INFINITY Explanation: When X (k) is given and x (N) is COMPUTED from it, the length of x (n) is increased to infinity.

Discussion

4.	The signal is reconstructed back with the help of(a) Zero order hold circuits(b) Extrapolations(c) Signal is reconstructed with zero order holds and extrapolations(d) Signal is not reconstructedThe question was asked during an online exam.Question is taken from Signal Reconstruction in portion Digital Control Systems of Control Systems
Answer» Right answer is (c) SIGNAL is reconstructed with zero order HOLDS and extrapolations To explain I would say: The signal is reconstructed that is the process of converting the discrete time signals into the continuous time signals and this can be DONE with the HELP of hold circuits or extrapolations.

Discussion

5.	Homogeneous solution of: y(n) -9/16y(n-2) = x(n-1)(a) C1(3/4)^n+C2(3/4)^-n(b) C1-(3/4)^n-1+C2(3/4)^n-1(c) C1(3/4)^n(d) C1-(3/4)^nI got this question in semester exam.My question is from The inverse z-transform and Response of Linear Discrete Systrems topic in chapter Digital Control Systems of Control Systems
Answer» Right answer is (a) C1(3/4)^n+C2(3/4)^-n The best explanation: TAKING the z-transform of the given DIFFERENCE EQUATION and solving the homogeneous equation and finding the SOLUTION using complimentary function.

Discussion

6.	Sampling is necessary :(a) In complex control systems(b) Where high accuracy is required(c) Non automated control systems(d) Automated control systemI got this question in a job interview.My query is from Signal Reconstruction topic in section Digital Control Systems of Control Systems
Answer» The correct option is (b) Where high ACCURACY is required The best explanation: Sampling is the process where the continuous systems are converted into discrete time systems with the HELP of zero ORDER hold of the signal and sampling is NECESSARY where high accuracy is needed.

Discussion

7.	Increased pulse-width in the flat-top sampling leads to:(a) Attenuation of high frequencies in reproduction(b) Attenuation of low frequencies in reproduction(c) Greater aliasing errors in reproduction(d) No harmful effects in reproductionThe question was asked during a job interview.This question is from Spectrum Analysis of Sampling Process in chapter Digital Control Systems of Control Systems
Answer» Correct choice is (a) ATTENUATION of HIGH frequencies in reproduction Explanation: As pulse width is increased, the width of the FIRST lobe of the SPECTRUM is DECREASED. Hence, increased pulse-width in the flat-top sampling, leads to attenuation of high frequencies in reproduction.

Discussion

8.	Convolution is used to find:(a) The impulse response of an LTI System(b) Frequency response of a System(c) The time response of a LTI system(d) The phase response of a LTI systemThis question was addressed to me in quiz.My query is from The Z-transform Analysis of Sampled-Data Control Systems in division Digital Control Systems of Control Systems
Answer» The correct answer is (c) The time RESPONSE of a LTI system To explain: Convolution is the combination of ADDITION and multiplication of the signals and USED to find the IMPULSE response of the LTI system.

Discussion

9.	If the z transform of x(n) is X(z) =z(8z-7)/4z^2-7z+3, then the final value theorem is :(a) 1(b) 2(c) ∞(d) 0I got this question in an interview.This question is from The inverse z-transform and Response of Linear Discrete Systrems topic in section Digital Control Systems of Control Systems
Answer» Correct ANSWER is (a) 1 For explanation I would say: Final VALUE theorem is calculated for the transfer FUNCTION by equating the value of Z as 1 and this can be calculated only for stable systems.

Discussion

10.	Which one of the following rules determine the mapping of s-plane to z-plane?(a) Right side of the s-plane maps into outside of the unit circle in z-plane(b) Left half of s-plane maps into inside of the unit circle(c) Imaginary axis in s-plane maps into the circumference of the unit circle(d) All of the mentionedI have been asked this question in homework.I'd like to ask this question from The Z-Transfer Function topic in division Digital Control Systems of Control Systems
Answer» CORRECT OPTION is (d) All of the mentioned For explanation: S- plane can be mapped into the z plane with certain rules than right side maps into the OUTSIDE, left side maps into the inside and imaginary axis maps on the unit CIRCLE of the z plane.

Discussion

11.	The first step required to convert analog signal to digital is :(a) Sampling(b) Holding(c) Reconstruction(d) QuantizationThis question was posed to me in an internship interview.This interesting question is from Signal Reconstruction topic in division Digital Control Systems of Control Systems
Answer» Correct choice is (a) Sampling Best EXPLANATION: Sampling is the process in which the continuous systems are sampled by the application of the zero order hold and is the first step in the CONVERSION of ANALOG to digital SIGNALS.

Discussion

12.	What is the z-transform of the signal x[n] = a^nu(n)?(a) X(z) =1/z-1(b) X(z) = 1/1-z(c) X(z) = z/z-a(d) X(z) = 1/z-aThis question was addressed to me during an internship interview.This key question is from The Z-Transfer Function topic in chapter Digital Control Systems of Control Systems
Answer» The CORRECT OPTION is (C) X(z) = z/z-a Explanation: By definition this is the basic example of the z-transform and the Z-Transform of the EQUATION is calculated is z/z-a.

Discussion

13.	Assertion (A): The signals a^nu(n) and a^nu(-n-1) have the same Z transform, z/(z-a)Reason (R): the region of convergence of a^nu(n) is \|z\|>\|a\|, whereas the ROC for a^nu(-n-1) is \|z\|(a) Both A and R are true and R is correct explanation of A(b) Both A and R are true but R is not correct explanationof A(c) A is true but R is false(d) A is false but R is trueThis question was posed to me during an interview for a job.I'm obligated to ask this question of The Z-Transfer Function in portion Digital Control Systems of Control Systems
Answer» Right ANSWER is (d) A is false but R is true The best I can explain: Both have the ROC as given in the reason is true but the z TRANSFORM for the SECOND is with a MINUS SIGN.

Discussion

14.	Statement (I): Aliasing occurs when the sampling frequency is less than twice the maximum frequency in the signal.Statement (II): Aliasing is a reversible process.(a) Both statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I).(b) Both Statement (I) and Statement (II) are individually true but Statement (II) is not correct explanation of Statement (I)(c) Statement (I) is true but Statement (II) is false(d) Statement (I) is False but Statement (II) is trueI have been asked this question in an interview for internship.My doubt is from Spectrum Analysis of Sampling Process in section Digital Control Systems of Control Systems
Answer» Correct CHOICE is (c) Statement (I) is true but Statement (II) is false To explain I would say: ALIASING is an irreversible process. Once aliasing has occurred then signal can-not be recovered back.

Discussion

15.	The system characterized by the equation y(t) = ax(t) + b is(a) Linear for any value of b(b) Linear if b > 0(c) Linear if b < 0(d) Non-linearThis question was addressed to me by my college director while I was bunking the class.This question is from The z- and s-Domain Relationship in section Digital Control Systems of Control Systems
Answer» Right choice is (d) Non-linear The explanation: The system is non-linear because X(t) = 0 does not lead to y (t) = 0, which is a VIOLATION of the PRINCIPLE of homogeneity.

Discussion

16.	First column elements of the Routh’s tabulation are 3, 5, -3/4, ½, 2. It means that there are:(a) Is one root in the left half of s-plane(b) Are two roots in the left half of s-plane(c) Are two roots in the right half of the s-plane(d) Is one root in the right half of s-planeThe question was posed to me by my college professor while I was bunking the class.I'm obligated to ask this question of Stability Analysis in portion Digital Control Systems of Control Systems
Answer» CORRECT choice is (c) Are two roots in the right half of the s-plane Explanation: Routh HURWITZ criteria is used to find the stability of the system and this is determined by the NUMBER of roots in which the number of roots is EQUAL to the number of SIGN changes.

Discussion

17.	Assertion (A): The closed loop stability can be determined from the poles of an open loop system and the polar plot of the frequency response.Reason (R): Unstable system has right half poles.(a) Both A and R are true and R is correct explanation of A(b) Both A and R are true and R is not correct Explanation of A(c) A is True and R is false(d) A is False and R is trueThe question was posed to me in quiz.My enquiry is from Compensation Techniques in section Digital Control Systems of Control Systems
Answer» Right option is (B) Both A and R are true and R is not correct Explanation of A To explain I WOULD say: CLOSED loop system can be made stable if the POLES of the closed loop system are all lying on the left half of the plane and this can be determined from the poles of an open loop system.

Discussion

18.	Which one of the following is the correct statement? The region of convergence of z-transform of x[n] consists of the values of z for which x[n]is:(a) Absolutely integrable(b) Absolutely summable(c) Unity(d)
Answer» Right OPTION is (B) Absolutely summable The EXPLANATION: The region of CONVERGENCE of z-transform of X[n] consists of the values of z for which x[n]r^-nis absolutely summable.

Discussion

19.	Signal sampling reduces the power demand made on the signal.(a) True(b) FalseI have been asked this question in exam.The query is from Signal Reconstruction topic in chapter Digital Control Systems of Control Systems
Answer» The correct OPTION is (a) True Explanation: Signal SAMPLING refers to the sampling of the signal and reduces the POWER demand that is the power required by the signal and is therefore HELPFUL for signals of weak origin.

Discussion

20.	The frequency of a continuous time signal x (t) changes on transformation from x (t) to x (α t), α > 0 by a factor(a) α(b) 1/α(c) α^2(d) αI have been asked this question in an interview for job.This question is from The Z-Transform in division Digital Control Systems of Control Systems
Answer» Correct ANSWER is (a) α For explanation I WOULD say: x(t)->x(αt), α > 0 α > 1 compression in t, expansion in f by α. α < 1 expansion in t, compression in f by α.

Discussion

21.	Zero-order hold used in practical reconstruction of continuous-time signals is mathematically represented as a weighted-sum of rectangular pulses shifted by:(a) Any multiples of the sampling interval(b) Integer multiples of the sampling interval(c) One sampling interval(d) 1 second intervalsI got this question during an interview.My question is from The Z-transform Analysis of Sampled-Data Control Systems in section Digital Control Systems of Control Systems
Answer» RIGHT choice is (b) Integer MULTIPLES of the sampling interval For explanation: Zero-order HOLD is used to reconstruct the continuous-time signal which is represented as a weighted sum of rectangular PULSES shifted by integer multiples of the sampling interval.

Discussion

22.	The order of a linear constant-coefficient differential equation representing a system refers to the number of(a) Active devices(b) Elements including sources(c) Passive devices(d) None of the mentionedThe question was posed to me in an interview for internship.My query is from The z- and s-Domain Relationship in portion Digital Control Systems of Control Systems
Answer» The CORRECT choice is (d) None of the mentioned Explanation: The order of the DIFFERENTIAL equation is the power of the highest order of the differential term and which refersto the NUMBER of POLES in the transfer function and practically it refers to the number of components that are energy storing elements .

Discussion

23.	Final value theorem is used for:(a) All type of systems(b) Stable systems(c) Unstable systems(d) Marginally stable systemsI have been asked this question in quiz.My enquiry is from The inverse z-transform and Response of Linear Discrete Systrems in portion Digital Control Systems of Control Systems
Answer» Right choice is (b) Stable SYSTEMS Best explanation: Final VALUE theorem is used to CALCULATE the final value as for time infinite and for Z = 1 the final value theorem can be calculated and final value theorem is for for stable systems.

Discussion

24.	The poles of a digital filter with linear phase response can lie(a) Only at z =0(b) Only on the unit circle(c) Only inside the unit circle but not at z =0(d) On the left side of Real (z) =0 lineThis question was posed to me in final exam.This intriguing question comes from Difference Equations topic in chapter Digital Control Systems of Control Systems
Answer» Right CHOICE is (b) Only on the unit circle The best I can explain: For stable systems the poles in z plane must lie INSIDE or on the unit circle and Minimum NUMBER of delay ELEMENTS = (Maximum power of z)-(minimum power of z).

Discussion

25.	Difference equation technique for higher order systems is used in:(a) Laplace transform(b) Fourier transform(c) Z-transform(d) None of the mentionedThis question was posed to me during an online interview.My doubt stems from Difference Equations in section Digital Control Systems of Control Systems
Answer» The correct OPTION is (C) Z-transform The best I can explain: For higher order systems Z- transform which is transforming discrete TIME domain into z domain and is technique is convenient for analysis and DESIGN of linear sampled data systems.

Discussion

26.	Sampling can be done by:(a) Impulse train sampling(b) Natural sampling(c) Flat-top sampling(d) All of the mentionedThe question was posed to me in final exam.My enquiry is from Signal Reconstruction in chapter Digital Control Systems of Control Systems
Answer» Right option is (d) All of the mentioned For explanation: SAMPLING is the process in which the continuous SYSTEMS are sampled by the application of the ZERO order hold and can be done by all the three METHODS.

Discussion

27.	Difference equation solution yields at the sampling instants only:(a) True(b) FalseI have been asked this question in examination.I would like to ask this question from Difference Equations topic in chapter Digital Control Systems of Control Systems
Answer» Right answer is (a) True Easy explanation: Difference EQUATION are the equations used in discrete TIME systems and difference equations are similar to the DIFFERENTIAL equation in continuous systems SOLUTION yields at the sampling instants only.

Discussion

28.	Z-transform converts convolution of time-signals to(a) Addition(b) Subtraction(c) Multiplication(d) DivisionThis question was posed to me by my college director while I was bunking the class.The origin of the question is The z- and s-Domain Relationship topic in chapter Digital Control Systems of Control Systems
Answer» The correct OPTION is (c) Multiplication Explanation: Convolution is the combination of ADDITION and multiplication that is between the same signal or the different SIGNALS and convolution in time domain is always multiplication in Z domain.

Discussion

29.	The FT of a rectangular pulse existing between t = − T 2/ to t = T / 2 is a(a) Sinc squared function(b) Sinc function(c) Sine squared function(d) Sine functionThis question was posed to me in an online interview.My question is from The z- and s-Domain Relationship topic in section Digital Control Systems of Control Systems
Answer» Right CHOICE is (b) Sinc FUNCTION The best I can explain: By definition the Fourier transform is the transformation of TIME domain of SIGNAL to FREQUENCY domain and that of a rectangular pulse is a sinc function.

Discussion

30.	Inverse z-transform of the system can be calculated using:(a) Partial fraction method(b) Long division method(c) Basic formula of the z-transform(d) All of the mentionedThis question was posed to me in final exam.I'm obligated to ask this question of The inverse z-transform and Response of Linear Discrete Systrems in division Digital Control Systems of Control Systems
Answer» Right OPTION is (d) All of the mentioned Easy explanation: Inverse z-transform is the opposite method of converting the transfer FUNCTION in Z DOMAIN to the discrete TIME domain and this can be calculated using all the above formulas.

Discussion

31.	What is the number of roots of the polynomial F(z) = 4z^3-8z^2-z+2, lying outside the unit circle?(a) 0(b) 1(c) 2(d) 3This question was addressed to me in homework.This key question is from The Z-Transfer Function topic in portion Digital Control Systems of Control Systems
Answer» Correct choice is (B) 1 Easy explanation: Factorizing F (Z) and then the FACTORS are the roots which here come out to be 3.

Discussion

32.	The characteristic equation of a control system is given by s^5+s^4+2s^3+2s^2+4s+6=0. The number of the roots of the equation which lie on the right half of s-plane:(a) 0(b) 1(c) 2(d) 3This question was addressed to me in final exam.My query is from Compensation Techniques in section Digital Control Systems of Control Systems
Answer» Correct answer is (c) 2 For explanation: The SOLUTION is obtained by using the Routh-Hurwitz table in which with the conventional method the number of SIGN changes are SEEN in the first row of the table and number of sign changes is EQUAL to the number of the roots on the RIGHT half of s plane.

Discussion

33.	The following characteristic equation results in stable operation of the feedback system s^3+4s^2+10s+11=0(a) True(b) FalseI got this question in homework.My question is from Stability Analysis topic in portion Digital Control Systems of Control Systems
Answer» The correct option is (a) True Easiest EXPLANATION: STABLE OPERATION can be CHECKED using the Routh-Hurwitz criterion where the FIRST row of the the table is checked and with that.

Discussion

34.	Given a unit step function u (t), its time-derivative is:(a) A unit impulse(b) Another step function(c) A unit ramp function(d) A sine functionThe question was posed to me in unit test.This interesting question is from The z- and s-Domain Relationship topic in division Digital Control Systems of Control Systems
Answer» Right choice is (a) A unit impulse The best I can EXPLAIN: Unit step function is ONE of the test signals and for the BASIC STANDARD signals they are INTERRELATED as the function of differentiation and integration as unit step function is the integral of impulse function.

Discussion

35.	Assertion (A): An LTI discrete system represented by the difference equation. y (n+2)-5y(n+1)+6y(n) =x(n) is unstable.Reason (R): A system is unstable if the roots of the characteristic equation lie outside the unit circle.(a) Both A and R are true and R is the correct explanation of A(b) Both A and R are true but R is NOT the correct explanation of A(c) A is true but R is false(d) A is false but R is falseThe question was posed to me in an interview for job.Enquiry is from Difference Equations topic in portion Digital Control Systems of Control Systems
Answer» The correct ANSWER is (a) Both A and R are true and R is the correct explanation of A To elaborate: Difference equation is y (n+2)-5 y (n+1) + 6 y (n) =x (n). Taking z-transform, H (z) =1/ (z-2) (z-3). The characteristic equation has roots z =2, 3. Since, the characteristic equation has roots OUTSIDE the unit circle, HENCE the system is unstable.

Discussion

36.	Assertion (A): The stability of the system is assured if the ROC includes the unit circle in z-plane.Reason (R): For a causal stable system all the poles should be outside the unit circle in the z-plane.(a) Both A and R are true and R is the correct explanation of A(b) Both A and R are true bit R is NOT the correct explanation of A(c) A is true but R is false(d) A is false but R is trueI have been asked this question during an internship interview.The doubt is from Difference Equations topic in division Digital Control Systems of Control Systems
Answer» Correct ANSWER is (c) A is TRUE but R is false For explanation I would say: A causal system LTI system is STABLE if and only if all of poles of H(Z) lie inside the UNIT circle.

Discussion

37.	The discrete-time signal x (n) = (-1)^n is periodic with fundamental period(a) 6(b) 4(c) 2(d) 0I got this question in a national level competition.The above asked question is from The Z-Transform in division Digital Control Systems of Control Systems
Answer» Right answer is (c) 2 The explanation: PERIOD of the SIGNAL refers to the instant of TIME at which the signal REPEATS itself and for this Period =2 of the GIVEN discrete time signal.

Discussion

38.	Let x(t) be a continuous-time, real valued signal band-limited to F Hz. The Nyquist sampling rate in Hz, For y(t) =x(0.5t) +x(t)-x(2t) is(a) F(b) 2F(c) 4F(d) 8FThe question was posed to me during an interview for a job.The above asked question is from Spectrum Analysis of Sampling Process topic in chapter Digital Control Systems of Control Systems
Answer» Right choice is (C) 4F The best explanation: Expansion in time domain in COMPRESSION in frequency domain and vice-versa. So, the MAXIMUM frequency component in given SIGNAL is 2F Hz. And according to sampling theorem. Nyquist rate =2FM =4F Hz.

Discussion

39.	How many roots with positive real parts do the equation s^3+s^2-s+1=0 have?(a) 0(b) 1(c) 2(d) 3The question was posed to me in unit test.Origin of the question is Compensation Techniques in section Digital Control Systems of Control Systems
Answer» The correct OPTION is (c) 2 Best EXPLANATION: The roots with positive real PARTS are calculated with the help of the routh-hurwitz table and since the sign changes two TIMES in first COLUMN therefore have two roots have positive parts.

Discussion

40.	For what values of K does the polynomial s^4+8s^3+24s^2+32s+K=0 have roots with zero real parts?(a) 10(b) 20(c) 40(d) 80I have been asked this question in an internship interview.My enquiry is from Compensation Techniques topic in section Digital Control Systems of Control Systems
Answer» Right answer is (d) 80 For explanation I WOULD SAY: The solution is OBTAINED by using the Routh-Hurwitz table and in which with the conventional method the number of sign changes are seen in the FIRST row of the table and number of sign changes is equal to the number of the roots on the right HALF of s plane.

Discussion

41.	The system having input x (n) related to output y(n) as y (n) = log \|x (n)\| is:(a) Nonlinear, causal, stable(b) Linear, noncausal, stable(c) Nonlinear, causal, not stable(d) Linear, noncausal, not stableI got this question in an online quiz.I would like to ask this question from The Z-transform Analysis of Sampled-Data Control Systems in chapter Digital Control Systems of Control Systems
Answer» The CORRECT option is (a) Nonlinear, causal, stable Explanation: As y (n) is the FUNCTION of x (n) hence it is nonlinear but it is BOUNDED and also depends UPON PAST and present values therefore it is stable and causal respectively.

Discussion

42.	The Routh-Hurwitz criterion cannot be applied when the characteristic equation of the system contains any coefficients which is :(a) Negative real and exponential function(b) Negative real, both exponential and sinusoidal function of s(c) Both exponential and sinusoidal function of s(d) Complex, both exponential and sinusoidal function of sI have been asked this question in homework.My query is from Stability Analysis topic in section Digital Control Systems of Control Systems
Answer» Right ANSWER is (b) NEGATIVE real, both exponential and sinusoidal function of s The BEST explanation: The Routh-Hurwitz criterion cannot be APPLIED when the CHARACTERISTIC equation of the system contains any coefficients which is negative real, both exponential and sinusoidal function of s.

Discussion

43.	The continuous time system described by 2 y(t) = x (t^2) is(a) Causal, linear and time varying(b) Causal, non-linear and time varying(c) Non causal, non-linear and time-invariant(d) Non causal, linear and time-invariantI had been asked this question in an online interview.The above asked question is from The z- and s-Domain Relationship topic in section Digital Control Systems of Control Systems
Answer» The correct choice is (d) Non CAUSAL, linear and time-invariant Best explanation: Y (t) depends upon the future value therefore the SYSTEM is ANTICIPATIVE and hence is not causal. But as it follows the SUPERPOSITION theorem so it is linear.

Discussion

44.	If the Fourier series coefficients of a signal are periodic then the signal must be(a) Continuous-time, periodic(b) Discrete-time, periodic(c) Continuous-time, non-periodic(d) Discrete-time, non-periodicThe question was asked in unit test.I need to ask this question from The Z-transform Analysis of Sampled-Data Control Systems in portion Digital Control Systems of Control Systems
Answer» Correct OPTION is (b) Discrete-time, periodic The BEST I can EXPLAIN: Discrete-time, periodic these are the properties of the discrete-time periodic signal.

Discussion

45.	When two honest coins are simultaneously tossed, the probability of two heads on any given trial is:(a) 1(b) 3/4(c) 1/2(d) ¼This question was addressed to me during an interview.My enquiry is from The Z-transform Analysis of Sampled-Data Control Systems in section Digital Control Systems of Control Systems
Answer» Right CHOICE is (d) ¼ The BEST I can explain: TOTAL outcomes =4 Favorable outcomes =1 Hence probability =1/4.

Discussion

46.	The use of sampled data control system are:(a) For using analog components as the part of the control loop(b) For time division of control components(c) Whenever a transmission channel forms a part of closed loop(d) None of the mentionedI have been asked this question in an online interview.The query is from Signal Reconstruction topic in division Digital Control Systems of Control Systems
Answer» The correct choice is (c) Whenever a transmission CHANNEL forms a part of closed loop To explain I would say: SAMPLED DATA control SYSTEM is the system where the data used is sampled and is used whenever a transmission channel forms a part of closed loop system.

Discussion

47.	The auto-correlation function of a rectangular pulse of duration T is(a) A rectangular pulse of duration T(b) A rectangular pulse of duration 2T(c) A triangular pulse of duration T(d) A triangular pulse of duration 2TI got this question at a job interview.My doubt is from The z- and s-Domain Relationship in section Digital Control Systems of Control Systems
Answer» RIGHT option is (d) A triangular PULSE of duration 2T Explanation: The auto-correlation function is the method of correlating the VARIOUS instants of the SIGNAL with itself and that of a rectangular pulse of duration T is a triangular pulse of duration 2T.

Discussion

48.	The z-transform corresponding to the Laplace transform G(s) =10/s(s+5) isThe question was posed to me in homework.I want to ask this question from The inverse z-transform and Response of Linear Discrete Systrems in division Digital Control Systems of Control Systems
Answer»

Discussion

49.	H (z) is discrete rational transfer function. To ensure that both H(z) and its inverse are stable:(a) Poles must be inside the unit circle and zeros must be outside the unit circle(b) Poles and zeroes must be inside the unit circle(c) Poles and zeroes must be outside the unit circle(d) Poles must be outside the unit circle and zeros must be inside the unit circleThe question was posed to me in exam.The doubt is from The Z-Transform in chapter Digital Control Systems of Control Systems
Answer» Correct option is (b) Poles and zeroes must be inside the unit CIRCLE The BEST I can EXPLAIN: For H(Z) to be STABLE the poles must be inside the unit circle and for the inverse of H(z) to be stable the poles of it must be inside the unit circle.

Discussion

50.	A signal represented by x(t) =5cos 400πt is sampled at a rate 300 samples/sec. The resulting samples are passed through an ideal low pass filter of cut-off frequency 150 Hz. Which of the following will be contained in the output of the LPF?(a) 100 Hz(b) 100 Hz, 150 Hz(c) 50 Hz, 100 Hz(d) 50 Hz, 100 Hz, 150 HzThis question was posed to me in an internship interview.The question is from Spectrum Analysis of Sampling Process topic in portion Digital Control Systems of Control Systems
Answer» The correct choice is (a) 100 Hz For explanation: X (t) =5cos400πt fm =200 Hz The output of the LPF will contain FREQUENCIES which are LESS than fc =150 Hz. So, fs-fm =300-200 =100 Hz is the only component PRESENT in the output of LPF.

Discussion

Explore topic-wise InterviewSolutions in .

Phase margin is always positive for stable feedback system?(a) True(b) FalseI had been asked this question in a job interview.The doubt is from Compensation Techniques topic in section Digital Control Systems of Control Systems

Sampling is necessary :(a) In complex control systems(b) Where high accuracy is required(c) Non automated control systems(d) Automated control systemI got this question in a job interview.My query is from Signal Reconstruction topic in section Digital Control Systems of Control Systems

If the z transform of x(n) is X(z) =z(8z-7)/4z^2-7z+3, then the final value theorem is :(a) 1(b) 2(c) ∞(d) 0I got this question in an interview.This question is from The inverse z-transform and Response of Linear Discrete Systrems topic in section Digital Control Systems of Control Systems

The first step required to convert analog signal to digital is :(a) Sampling(b) Holding(c) Reconstruction(d) QuantizationThis question was posed to me in an internship interview.This interesting question is from Signal Reconstruction topic in division Digital Control Systems of Control Systems

What is the z-transform of the signal x[n] = a^nu(n)?(a) X(z) =1/z-1(b) X(z) = 1/1-z(c) X(z) = z/z-a(d) X(z) = 1/z-aThis question was addressed to me during an internship interview.This key question is from The Z-Transfer Function topic in chapter Digital Control Systems of Control Systems

Which one of the following is the correct statement? The region of convergence of z-transform of x[n] consists of the values of z for which x[n]is:(a) Absolutely integrable(b) Absolutely summable(c) Unity(d)

Signal sampling reduces the power demand made on the signal.(a) True(b) FalseI have been asked this question in exam.The query is from Signal Reconstruction topic in chapter Digital Control Systems of Control Systems

The frequency of a continuous time signal x (t) changes on transformation from x (t) to x (α t), α > 0 by a factor(a) α(b) 1/α(c) α^2(d) αI have been asked this question in an interview for job.This question is from The Z-Transform in division Digital Control Systems of Control Systems

Final value theorem is used for:(a) All type of systems(b) Stable systems(c) Unstable systems(d) Marginally stable systemsI have been asked this question in quiz.My enquiry is from The inverse z-transform and Response of Linear Discrete Systrems in portion Digital Control Systems of Control Systems

Difference equation technique for higher order systems is used in:(a) Laplace transform(b) Fourier transform(c) Z-transform(d) None of the mentionedThis question was posed to me during an online interview.My doubt stems from Difference Equations in section Digital Control Systems of Control Systems

Sampling can be done by:(a) Impulse train sampling(b) Natural sampling(c) Flat-top sampling(d) All of the mentionedThe question was posed to me in final exam.My enquiry is from Signal Reconstruction in chapter Digital Control Systems of Control Systems

Difference equation solution yields at the sampling instants only:(a) True(b) FalseI have been asked this question in examination.I would like to ask this question from Difference Equations topic in chapter Digital Control Systems of Control Systems

What is the number of roots of the polynomial F(z) = 4z^3-8z^2-z+2, lying outside the unit circle?(a) 0(b) 1(c) 2(d) 3This question was addressed to me in homework.This key question is from The Z-Transfer Function topic in portion Digital Control Systems of Control Systems

The following characteristic equation results in stable operation of the feedback system s^3+4s^2+10s+11=0(a) True(b) FalseI got this question in homework.My question is from Stability Analysis topic in portion Digital Control Systems of Control Systems

The discrete-time signal x (n) = (-1)^n is periodic with fundamental period(a) 6(b) 4(c) 2(d) 0I got this question in a national level competition.The above asked question is from The Z-Transform in division Digital Control Systems of Control Systems

How many roots with positive real parts do the equation s^3+s^2-s+1=0 have?(a) 0(b) 1(c) 2(d) 3The question was posed to me in unit test.Origin of the question is Compensation Techniques in section Digital Control Systems of Control Systems

For what values of K does the polynomial s^4+8s^3+24s^2+32s+K=0 have roots with zero real parts?(a) 10(b) 20(c) 40(d) 80I have been asked this question in an internship interview.My enquiry is from Compensation Techniques topic in section Digital Control Systems of Control Systems

The z-transform corresponding to the Laplace transform G(s) =10/s(s+5) isThe question was posed to me in homework.I want to ask this question from The inverse z-transform and Response of Linear Discrete Systrems in division Digital Control Systems of Control Systems