# Recent questions and answers in Control System

What are the advantages of open loop control system?

What is Mason's gain formula?

The open loop control system is one in which _____.

What are some examples of a closed loop system?

What is an example of an open loop system?

what is open loop and close loop control system?

With negative feedback, the system stability and system gain respectively (a) Increases and increases (b) Increases and decreases (c) Decreases and increases (d) Decreases and decreases

The effect of negative feedback on distortion and bandwidth is A) Both distortion and bandwidth get decreased B) Both distortion and bandwidth get increased C) Distortion is reduced and bandwidth is increased D) Distortion is increased and bandwidth is decreased

What will happen to the gain margin if the gain of the open loop system is doubled? A) Doubled B) Becomes half C) Is not affected D) Becomes one-fourth

What is the time response of a system whose poles lie on the right hand side of s-plane? A) Exponentially increasing B) Exponentially decreasing C) Sinusoidal oscillations D) Step response

What is the steady state error of type-0 system for ramp input?  A) ∞ B) A/K C) A/(1+K) D) 0

A system is critically damped. If the gain of the system is increased, the system will behave as: A) overdamped B) underdamped C) oscillatory D) critically damped

A lag-lead compensator for a second order system (A) improves steady state errors, reduces relative stability (B) marginally improves steady state errors, increases relative stability (C) reduces steady state errors, increases relative stability (D) improves both transient response and steady state response

A PD controller is used to compensate a system. Compared to the uncompensated system, the compensated system has: (1) A higher type number. (2) Reduced damping. (3) Higher noise amplification. (4) Larger transient overshoot.

Which one most appropriate dynamic system? (1) y(n) + y(n – 1) + y(n + 1) (2) y(n) + y(n – 1) (3) y(n) = x(n) (4) y(n) + y(n – 1) + y(n + 3) = 0

Synchros in control systems are used as (a) error detectors (b) encoders (c) both (a) and (b) (d) none of these

For a desirable transient response of a second order system, the damping ratio must be between (a) 0.4 and 0.8 (b) 0.8 and 1.0 (c) 0.3 and 0.5 (d) 0.2 and 0.4

In a control system, the comparator measures the difference between (a) output and input (b) output of controller and system (c) actual and desired performance (d) input and error signal

The best method for determining the stability and transient response of a control system is (a) Bode Plot (b) Nyquist plot (c) Root locus (d) Routh-Hurwitz

A system with gain margin close to unity or a phase margin close to zero is (a) conditionally stable (b) relatively stable (c) highly stable (d) highly oscillatory

In force-current analogy, analogous of displacement is (a) charge (b) flux linkage (c) voltage (d) current density

By increasing the gain ‘k’ of a system, steady state error of the system (a) increases (b) decreases (c) remains unaffected (d) nothing can be said

The sensitivity of a closed loop system to gain changes and load disturbances depends upon (a) forward gain (b) loop gain (c) frequency (d) all the above

In a closed loop control system  (a) control action depends upon the output and also on the input command (b) output signal is fed back to be compared with the reference signal (c) the accuracy is better than in the open loop system (d) all of the above

Companding is a technique used to achieve: -  a) uniform quantization b) delta modulation c) non uniform quantization d) differential quantization

For a stable feedback control system, the phase margin is  a) always positive b) always negative c) may be positive or negative d) always greater than 180o

In root locus plot, a point on the real axis lies on the locus, if the number of open loop poles plus zeros on real axis to the a) left of the point is odd b) left of the point is even . c) right of the pointis odd d) right of the point is even

Introduction of integral action in the forward path of a unity feedback system results in a  A) Marginally stable system B) System with no steady state error C) System with increased stability margin D) System With better speed of response

For a feedback control system of type 2, the steady error for a rap input is  A) Infinite B) Constant C) Zero D) Indeterminate

The correct sequence of steps required to improve system stability is  (A) Insert derivative action, use negative feedback, reduce gain (B) Reduce gain, use negative feedback, insert derivative action (C) Reduce gain, insert derivative action, use negative feedback (D) Use negative feedback, reduce gain, insert derivative action

The driving point impedance with poles at ω = 0(zero) and ω = ∞ (infinity) must have the  (a) s term in the denominator and an excess term in the numerator (b) s term in the numerator and an excess term in the denominator (c) s term in the numerator and equal number of terms in the numerator and denominator (d) s term in the denominator and equal number of terms in the numerator and denominator

For a 2nd order feedback control system, the peak resonance magnitude should be Mp ≤ 1.15. Hence the damping ratio (δ) is  (a) 0.1 (d) 0.5 (c) 0.707 (d) 1

The characteristic equation for a closed loop system with forward gain K is s4 + 4s3 + 8s2 + 6s + K = 0. The critical gain value Kc for stability should not exceed  (a) 3.25 (b) 9.75 (c) 13.0 (d) 23.3

The loop transfer of a system is G(s) H(s) = 5/(s+1) (2s+1)(3s+1) which has the phase crossover frequency fc = 0.16 Hz. The gain margin (dB) of the system is  (a) 6 (b) 4 (c) 2 (d) 0

For a 2nd order servo system, the damping ratio δ = 0.5456 and undamped natural frequency is ωn = 31.6 rad/sec. The percent overshoot is  (a) 7.07 (b) 10.2 (c) 14.10 (d) 21.21

For a system with derivative feedback, forward path transfer is G(s) = I / (s2 + s + 1) and feedback path transfer is H(s) = Ks. What is the value of K to obtain a critically-damped closed loop transient response.  (a) 0.5 (b) 0.707 (c) 1 (d) 1.414

In lag compensator the damping ratio, gain and steady state error (ess) are   (a) Decreases, Decreases and Increases (b) Decreases, Increases and Increases (c) Increases, Increases and Decreases (d) Increases, Decreases and Decreases

The critical point lies within the nyquist plot then the system is   (a) Marginally stable (b) Unstable (c) Stable (d) Undetermined

The gain margin of a system is 0 dB. It represents a   (a) Stable system (b) Unstable system (c) Marginally stable system (d) Conditionally stable system

Order of the open loop transfer function is _____ to order of closed loop transfer function   (a) not equal (b) equal (c) less than (d) greater than

Poles are real and negative and equal then the system is _____ damped system   (a) Undamped (b) Underdamped (c) Critically damped (d) Overdamped

For the minimum phase system, which of these is the most appropriate one ?  (A) All poles are inside the unit circle in the z-plane  (B) All zeros are inside the unit circle in the z-plane  (C) All poles and zeros are inside the unit circle in the z-plane  (D) All poles and zeros are outside the unit circle in the z-plane

An absolutely integrable signal x(t) is known to have a pole at s = 2. Which one of the following is true ? (A) B, C and D are true (B) x(t) can be left-sided (C) x(t) can be right-sided (D) x(t) can be both-sided

If x(t) is of finite duration and absolutely integrable, the ROC of its Laplace Transform X(s) is (A) Left half-plane (B) Entire s-plane (C) Right half-plane (D) Finite duration plane

Let x1(t) and x2(t) be periodic with fundamental periods T1 and T2 respectively. Under what condition be the sum x(t) = x1(t) + x2(t) be periodic ? (A) Only for T1 = T2 (B) Always periodic (C) For T1/T2 equal to a rational number (D) Not periodic

Given a unity feedback system with G(s)=k/s (s+4), the value of k for damping ratio of 0.5 is

A system is linear if and only if it satisfies