Q1. What do you mean by transportation lag?
Ans. The transportation lag is the delay between the time an input signal is applied to a system and the time the system reacts to that input signal. Transportation lags are common in industrial applications. They are often called “dead time”.
Q2. How 2 phase AC servo motor-differs from normal induction motor?
Ans. 1. Rotor of servo motor is built with high resistance and X/R ratio is small. Due to this torque speed characteristic is nearly linear.
- Rotor inertia is kept low.
Q3. What is the value of ξ used in practical systems?
Ans. 0.6<ξ<0.8, which is a compromise between fast but oscillatory under-damped response and slow but without oscillations critically damped response.
Q4. If Pole is added closer to the origin,what is the effect on response of the system?
Ans. Addition of pole always tend to make system more sluggish and unstable so it should be always avoided to add a pole closer to origin.
Q5. What is the difference between peak-overshoot and resonant peak?
Ans. Resonant peak value is infinite at ξ = 0.707 while peak-overshoot dies at ξ = 1. Peak overshoot is a time domain characteristic while resonant peak is frequency domain characteristic.
Q6. If an unbounded input is applied to system and results in unbounded output then state whether system will be stable or not?
Ans. Since input is unbounded so we cannot comment about the stability of system. It may be stable and may be unstable ,for stability bounded input produces bounded output.\\
Q7. What is the difference between absolute and relative stability of a system?
Ans. Absolute stability just gives whether the system is stable or not while relative stability not only gives answer about stability but also tells the margin of stability.
Q8. What are the time domain methods of determining stability of a system?
Ans. Routh stability criterion and root locus are time domain methods for determining the stability of a system..
Q9. What are frequency domain methods to determine the stability of a system?
Ans. Polar plot,Nyquist Plot, Bode Plot, Nichlos Chart and Constant M-N circle are frequency domain methods to determine the stability of a system.
Q10. Which method is best suitable for showing the change in behavior of a system when a pole is added or removed from system?
Ans. Root Locus is best method.
Q11. Bode Plot is suitable for which type of system,minimum phase or non-minimum phase?
Ans. It is suitable only for minimum phase transfer function systems.
Q12. If the order of system increases what happens to stability and steady state error of that system?
Ans. With increase in order of system both stability as well as steady state error decreases.
Q13. What is the difference between controller and compensator?
Ans. Both controller and compensator has the function of improving the stability and response of the system. But controller is incorporated in the system during its manufacturing while compensator is incorporated when system fails to work according to specifications i.e.during its operation.
Q14. What is peak overshoot? Is it desirable?
Ans. Difference between the maximum value attained by a response and final value of response, is known as peak overshoot. It should be as low as possible because it increases noise in the system.
Q15. What is the disadvantage of using a PD controller?
Ans. A PD controller is basically HPF. So it has large bandwidth and amplifies more noise and this deteriorates the SNR of system.
Q16. Nyquist plot is symmetric with respect to real axis. Why?
Ans. Nyquist plot is suitable for Linear Time Invariant system that’s why it is symmetric, as the transfer function is rational with real coefficient polynomials.
Q17. What is the difference between derivative feedback controller and derivative controller?
Ans. In derivative controller, actuating signal is proportional to the derivative of error signal while in derivative feedback controller, actuating signal is proportional to the derivative of output signal and is connected in feedback path.
Q18. What will happen to Bode plot when gain ,K < 0?
Ans. There is no effect on magnitude plot but a phase of – 180o is provided by K term to phase plot.
Q19. Why PI controller is rarely used?
Ans. A PI controller decreases the steady state error of system but it increases the order of system and hence tends to destabilize it.
Q20. Is their difference between polar plot and Nyquist plot?
Ans. A polar plot is sub-part of Nyqist plot. A Nyquist plot varies from ω = 0 to ω = ∞, ω = ∞, to ω = - ∞, and finally ω = - ∞, to ω = ∞, while polar plot varies from ω = 0 to ω = ∞ only(positive frequencies only).
Q21. What happens to stability and steady state error when the gain of a system is increased ?
Ans. With increase in gain, stability as well as steady state error of system decreases.
Q22. As rise time of a system increases, what happens to speed?
Ans. Since, so as rise time increases bandwidth of system decreases so is the speed.
Q23. Which system is always stable?
Ans. A second order with stable subsystems is always stable and poles are in LHS of s-plane.
Q24. Why transfer function approach is not suitable for dynamic systems?
Ans. Transfer function approach of system response analysis do not consider the initial conditions of system and dynamic systems are not LTI system and also possess initial conditions.
Q25. As type of a system increases, _______ number inputs can be applied to it.
Ans. As the type of system increases, the steady state error decreases so more number of inputs can be applied to the system.
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