20 + Interview Questions in Error Analysis in Control Systems Page 1 InterviewSolution

1.	What is the response of the feedback function with open loop transfer function G(s) = 4/s(s+5) and input is input step?(a) 1-1/3(4e^-t – e^-4t)(b) 1-1/2(6e^-t – e^-4t)(c) 1-1/3(6e^-t – e^-4t)(d) 1-1/2(4e^-t – e^4t)This question was posed to me in semester exam.This intriguing question comes from Integral Square Error & its Minimization topic in chapter Error Analysis of Control Systems
Answer» Correct option is (a) 1-1/3(4e^-t – e^-4t) Easiest explanation: We should FIRST GET the response in s domain which is C(s)/R(s) = G(s)/1+G(s) = R(s) 4/(s+1)(s+4) and as the input is unit step which R(s)=1/s the equation becomes 4/s(s+1)(s+4). Then we APPLY partial fraction to the equation and we get values of A, B, C as 1, -4/3, 1/3 and then inverse Laplace TRANSFORM is applied to C(s) and we get response as1-1/3(4e^-t – e^-4t).

Discussion

2.	The steady state error for a unity feedback system for the input r(t) to the system G(s) =K(s+2)/s(s^3+7s^2+12s) is 6R/K. The input r (t) is _______(a) Rt2/2(b) Rt3/2(c) Rt5/2(d) Rt7/2The question was asked in an international level competition.The origin of the question is Steady State Error in division Error Analysis of Control Systems
Answer» Correct choice is (a) Rt2/2 The best explanation: Ka = 2K/12 = K/6. Ess = 6R/K. So, as we TAKE Rt^2/2 we GET 6R/K as the error. The other options can’t be true because the INPUT is EXCEEDING the desired input. It is inversely proportional to the GAIN.

Discussion

3.	For a unity feedback control system, the open loop transfer function G(s) = 10(s+2)/s^2(s+1). What is the acceleration error constant?(a) Infinity(b) 5(c) 10(d) 20I have been asked this question in an online interview.My doubt stems from Integral Square Error & its Minimization topic in portion Error Analysis of Control Systems
Answer» The correct option is (d) 20 The best EXPLANATION: As LIMIT s tends to zero s^2 G(s) H(s) = s^2 G(s) = 10*2/1 = 20. THEREFORE we get the value of KA as 20 and both kv and ks are infinity.

Discussion

4.	A performance index must offer selectivity.(a) True(b) FalseThis question was posed to me in an internship interview.This interesting question is from Integral Square Error & its Minimization topic in chapter Error Analysis of Control Systems
Answer» Right answer is (a) True Explanation: It must offer selectivity, that is, an OPTIMAL adjustment of parameters must CLEARLY distinguish non optimal adjustment of parameters. If there was no selectivity we WOULD not have been able to distinguish between parameters.

Discussion

5.	Systems of type higher than 1 are not employed in practice.(a) True(b) FalseThe question was posed to me in exam.This question is from Steady State Error in division Error Analysis of Control Systems
Answer» The correct choice is (b) False Explanation: SYSTEMS of TYPE higher than 2 are not employed in practice as they’re difficult to STABILIZE and DYNAMIC error increases. Systems of type 2 or lower are already STABLE and has less dynamic error.

Discussion

6.	What is the need for a controller?(a) Receive control signals(b) Transmit control signals(c) Modify control signals(d) Create control signalsI had been asked this question during an internship interview.My question is based upon Integral Square Error & its Minimization in section Error Analysis of Control Systems
Answer» RIGHT answer is (c) MODIFY control signals Explanation: Controller is needed to modify control signals for better control ACTION. Some control signals are raw signals which can’t function properly so we use controllers for modifying them.

Discussion

7.	The open loop transfer function for a unit feedback system is G(s) = K/s(sT+1). By what factor the amplitude gain K should be reduced so that the peak overshoot becomes 25% from 75%?(a) 75(b) 25(c) 20(d) 10I got this question in an internship interview.Query is from Integral Square Error & its Minimization in section Error Analysis of Control Systems
Answer» Correct choice is (c) 20 The explanation is: The peak overshoot is decreased by INCREASING the damping RATIO. The damping ratio is INCREASED by reducing the gain K by same proportion and for DECREASING the peak overshoot from 75% to 25% the factor of AMPLITUDE becomes 19.6% which is approximately 20%.

Discussion

8.	The Laplace transform of a parabolic signal is _______(a) 1(b) A/s^3(c) A/s^2(d) A/sI have been asked this question in an interview.Query is from Steady State Error in division Error Analysis of Control Systems
Answer» Correct option is (a) 1 For EXPLANATION: As u(t) is a unity STEP FUNCTION r(t)=0;t<0 and r(t)=1; t=0. The parabolic signal is a signal which has varying amplitudes and when we TAKE Laplace Transform of that we GET 1 as the answer.

Discussion

9.	For a unity feedback system, the open loop transfer function is G(s) = K(s+2)/s^2 (s^2+7s+12). What is the type of system?(a) One(b) Two(c) Three(d) FourI got this question at a job interview.My question is based upon Steady State Error in section Error Analysis of Control Systems
Answer» Right choice is (b) Two Explanation: As in the NUMERATOR it is mentioned K(s+2) so we GOT two poles in the open loop transfer function at the origin. For a GIVEN transfer function we calculate poles and ZEROS and the number of poles determine the type of the system.

Discussion

10.	The steady state error for a unit step input is ________(a) 1/kp(b) 1/(1-kp)(c) 1/2kp(d) 1/(1+kp)The question was posed to me during an online exam.Asked question is from Steady State Error topic in chapter Error Analysis of Control Systems
Answer» Right answer is (d) 1/(1+kp) For explanation I WOULD say: R(s) =1/s for unit step and for the TRANSFER FUNCTION whose limit tends to ZERO, it is 1/1+kp. We use Laplace and Inverse Laplace Transform to CALCULATE the same.

Discussion

11.	For a system whose transfer function is G(s) =10/s (1+s), what are the dynamic error coefficients k2 & k3 respectively as k1 is infinity?(a) 11, 10.1(b) 10.1, 11(c) 10, 11.1(d) 9, 10.1I got this question in my homework.Origin of the question is Steady State Error topic in portion Error Analysis of Control Systems
Answer» RIGHT answer is (c) 10, 11.1 The best explanation: We should COMPARE it with E(s)/R(s) = 1/k1+1/k2s+1/k3s^2.G(s) = 10/s(1+s) is compared with the above equation which is the PARENT equation for calculating dynamic error CONSTANTS where k1 comes as infinity and K2, K3 takes the value of 10 & 11.1 respectively.

Discussion

12.	The response of a servomechanism is 1+0.2e^-60t-1.2e^-10t when subjected to a unit step input. What is the damping ratio?(a) 1.21(b) 1.43(c) 1.59(d) 1.74The question was posed to me in an interview for job.My question is from Integral Square Error & its Minimization in section Error Analysis of Control Systems
Answer» The correct CHOICE is (b) 1.43 The best I can EXPLAIN: First we apply Laplace Transform to the system and as R(s) = 1/s we get closed loop transfer FUNCTION as C(s)/R(s) = 600/s^2+70s+600. Then we compare it with the standard equation for second ORDER transfer function we got damping ratio = 70/2wn = 1.43.

Discussion

13.	How many types of controllers and compensators are there respectively?(a) 4, 3(b) 3, 4(c) 4, 5(d) 5, 4This question was posed to me in an interview.This question is from Integral Square Error & its Minimization topic in chapter Error Analysis of Control Systems
Answer» Correct option is (a) 4, 3 Explanation: There are 4 types of controllers namely PID, PI, PD. There are 3 types of compensators namely LAG, LEAD & Lag-Lead compensators.

Discussion

14.	What is the analogous electrical element of Frictional coefficient (B) in Force-Current Analogy for mechanical translational system?(a) Resistance(b) Conductance(c) Flux(d) VoltageThis question was addressed to me during an interview.My enquiry is from Integral Square Error & its Minimization in chapter Error Analysis of Control Systems
Answer» The correct option is (b) Conductance For explanation I would SAY: As RESISTANCE is the analogous element of B in F-V analogy so here it is the reciprocal of resistance, conductance is the answer. Force voltage analogy MEANS both the EQUATIONS will have differential equation of the same form.

Discussion

15.	Actuator is the basic component of an automatic control system.(a) False(b) TrueThe question was posed to me during an online interview.Enquiry is from Integral Square Error & its Minimization in division Error Analysis of Control Systems
Answer» Right choice is (b) True The explanation: There are 5 basic components of an automatic control system. They are ERROR detector, AMPLIFIER, ACTUATOR, plant, and sensor. So, Actuator is a basic COMPONENT of automatic control system.

Discussion

16.	The ramp input is applied to a unity feedback system with type number 1 and zero frequency 20. What is the percentage of steady state error?(a) 1%(b) 2%(c) 5%(d) 9%I got this question at a job interview.My question is from Steady State Error in division Error Analysis of Control Systems
Answer» The correct option is (c) 5% To explain I WOULD say: Steady STATE error is the error calculated between the final output and desired output and the error must be less and this steady state error is inversely PROPORTIONAL to gain. Here unity FEEDBACK system is given with zero frequency 20 so we take 1/20^th part and the answer comes as 5%.

Discussion

17.	A unity feedback system has an open loop transfer function G(s) =25/s(s+8). What is the percentage of it’s peak overshoot?(a) 0.13%(b) 1.13%(c) 1.26%(d) 1.52%This question was posed to me in an international level competition.Question is from Integral Square Error & its Minimization in portion Error Analysis of Control Systems
Answer»

Discussion

18.	The For a unity feedback system the open loop transfer function is G(s) = K(s+2)/s^2 (s^2+7s+12). What is the value of Ka?(a) 12/k(b) k/12(c) k/6(d) 6/kThe question was posed to me in exam.This interesting question is from Steady State Error topic in chapter Error Analysis of Control Systems
Answer» Correct ANSWER is (c) k/6 For EXPLANATION: As limit s tends to zero :s^2G(s) = K(s+2)/ (s^2+7s+12) = k/6.Ka is the ACCELERATION error CONSTANT which is calculated by the above method.

Discussion

19.	The initial response when output is not equal to input is ______(a) Error response(b) Transient response(c) Dynamic response(d) Static responseThis question was posed to me by my school principal while I was bunking the class.The above asked question is from Steady State Error in portion Error Analysis of Control Systems
Answer» CORRECT choice is (b) Transient response Explanation: The response is not LONG last lasting and real, so it is a transient response. It can’t be a static or DYNAMIC response as the OUTPUT doesn’t match the input and ALSO there’s no chance of error response.

Discussion

20.	A unit integrator is applied to a modified system along with a ramp input. The modified value of the steady state error is 0.25. What was the initial value?(a) 0.05(b) 0.1(c) 0.15(d) 0.2I got this question during an internship interview.My question is based upon Steady State Error topic in section Error Analysis of Control Systems
Answer» Correct choice is (d) 0.2 Easy explanation: The INTEGRATOR is similar to the phase LAG systems and it is used to reduce or eliminate the steady state error and when it is cascaded with the ramp input. We know that when unit integrator is applied with a ramp input the steady state error will AUTOMATICALLY INCREASE but here we wanted the initial VALUE which will be obviously less than the modified steady state error and by the same proportion.

Discussion

Explore topic-wise InterviewSolutions in .

A performance index must offer selectivity.(a) True(b) FalseThis question was posed to me in an internship interview.This interesting question is from Integral Square Error & its Minimization topic in chapter Error Analysis of Control Systems

Systems of type higher than 1 are not employed in practice.(a) True(b) FalseThe question was posed to me in exam.This question is from Steady State Error in division Error Analysis of Control Systems

The Laplace transform of a parabolic signal is _______(a) 1(b) A/s^3(c) A/s^2(d) A/sI have been asked this question in an interview.Query is from Steady State Error in division Error Analysis of Control Systems

For a unity feedback system, the open loop transfer function is G(s) = K(s+2)/s^2 (s^2+7s+12). What is the type of system?(a) One(b) Two(c) Three(d) FourI got this question at a job interview.My question is based upon Steady State Error in section Error Analysis of Control Systems

The steady state error for a unit step input is ________(a) 1/kp(b) 1/(1-kp)(c) 1/2kp(d) 1/(1+kp)The question was posed to me during an online exam.Asked question is from Steady State Error topic in chapter Error Analysis of Control Systems

How many types of controllers and compensators are there respectively?(a) 4, 3(b) 3, 4(c) 4, 5(d) 5, 4This question was posed to me in an interview.This question is from Integral Square Error & its Minimization topic in chapter Error Analysis of Control Systems

Actuator is the basic component of an automatic control system.(a) False(b) TrueThe question was posed to me during an online interview.Enquiry is from Integral Square Error & its Minimization in division Error Analysis of Control Systems

The ramp input is applied to a unity feedback system with type number 1 and zero frequency 20. What is the percentage of steady state error?(a) 1%(b) 2%(c) 5%(d) 9%I got this question at a job interview.My question is from Steady State Error in division Error Analysis of Control Systems

The For a unity feedback system the open loop transfer function is G(s) = K(s+2)/s^2 (s^2+7s+12). What is the value of Ka?(a) 12/k(b) k/12(c) k/6(d) 6/kThe question was posed to me in exam.This interesting question is from Steady State Error topic in chapter Error Analysis of Control Systems