CONTROLLING ENGINEERING January 26, 2019 Vijayan 0 Control engineering or control systems engineering is an engineering discipline that applies automatic control theory to design systemswith desired behaviors in control environments. The discipline of controls overlaps and is usually taught along with electrical engineering at many institutions . Which of the following is an example of an open loop system? Household Refrigerator Respiratory system of an animal Execution of program by computer Stabilization of air pressure entering into the mask An object stationary or moving in a uniform motion w.r.t A will appear to be traveling in a straight path w.r.t B. This apparent path is attributed to Coriolis acceleration. True False The lagrangian is defined as: Sum of kinetic energy and hydraulic energy Mechanical energy Difference of kinetic and potential energy None of these In case of DC servomotor, the back emf is equivalent to an “electric friction” which tends to: Slowly decrease the stability of the system Improve stability of the system Very rapidly decrease the stability of the system Have no effect of stability Assertion (A): DC servomotors are more commonly used in armature controlled mode than field controlled mode.Reason (R): Armature controlled Dc motors have higher starting torque than fiels controlled motors. A is true but R is false Both A and R are true and R is the correct explanation of A Both A and R are true but R is not correct explanation of A A is false but R is true Gear train in the motor is used to reduce the gear ratio? True False For a tachometer, if a(t) is the rotor displacement, e(t) is the output voltage and K is the tachometer constant, then the transfer function is given by: Ks K Ks2 K/s Tachometer feedback in a D.C. position control system enhances stability? True False Backlash in a stable control system may cause: Under damping Over damping High level oscillations Low level oscillations The below figure represents: Lead network Lag network PI controller PD controller The output of an first order hold between two consecutive sampling instants is: Constant Quadratic Function Ramp Function Exponential Function Consider a simple mass spring friction system as given in the figure K1, K2 are spring constants f-friction, M-Mass, F-Force, x-Displacement. The transfer function X(s)/F(s) of the given system will be : 1/(Ms2+fs+K1.K2) 1/(Ms2+fs+K1+K2) 1/(Ms2+fs+K1.K2/K1+K2) K2/(Ms2+fs+K1) For the block diagram given in the following figure, the expression of C/R is: G1G2G3/1-G2G1 G1G2/1-G1G2G3 G1G2G3/1-G1G2G3 G1G2/G3(1-G1G2) The transfer function from D(s) to Y(s) is : 6/3s+7 2/3s+1 2/3s+6 2/3s+7 The overall transfer function from block diagram reduction for cascaded blocks is : Sum of individual gain Product of individual gain Difference of individual gain Division of individual gain The overall transfer function of two blocks in parallel are : Product of individual gain Sum of individual gain Difference of individual gainc Division of individual gain Transfer function of the system is defined as the ratio of Laplace output to Laplace input considering initial conditions________ 6 2 0 Infinite In the following block diagram, G1=10/s G2=10/s+1 H1=s+3, H2=1. The overall transfer function is given by : 10/11s2+31s+10 100/11s2+31s+100 100/11s2+31s+10 100/11s2+31s Oscillations in output response is due to : Negative feedback No feedback Positive feedback None of these Use mason’s gain formula to find the transfer function of the given signal flow graph: abd/1-(bc+ef)+bcef abd/1-(ac) adcdef/1-(bc+ef)+bcef abdeg/1-(bc+ef)+bcef Use mason’s gain formula to find the transfer function of the following signal flow graph: abcd+efg/1-cd-fg-cdfg adcdefg/1-cd-fg-cdfg abef+bcd/1-cd-fg-cdfg acdfg+bcefg/1-cd-fg-cdfg Loop which do not possess any common node are said to be ___________ loops. Touching loops Forward gain Non touching loops Feedback gain Which of the following is not the correct reason to select feedback compensation over cascaded one? No amplification is required as the energy transfer is from higher to lower level. It is economical Suitable devices are not available for compensation(series) Provides greater stiffness against load disturbances The transfer function of a phase-lead controller is given by (1+aTs)/(1+Ts) , a>1 T>0 (1+aTs)/(1+Ts) , a<1 T>0 (1-aTs)/(1+Ts) , a>1 T>0 (1±Ts)/(1+Ts) , a<1 T>0 Given a unity feedback control system with G (s) = K/s(s+4), the value of K for which the damping ratio is 0.5. 1 34 16 64 The LVDT is used in the measurement of: Displacement Acceleration Velocity Humidity A system with gain margin close to unity and phase margin close to zero is : Highly stable Oscillatory Relatively stable Unstable Consider a system if represented by state space equation and x1 (t) =x2 (t), then the Controllable Uncontrollable Observable Unstable A transfer function of the system does not have pole-zero cancellation? Which of the following statements is true? System is neither controllable nor observable System is completely controllable and observable System is observable but uncontrollable System is controllable and unobservable Complex conjugate pair: Center Focus point Saddle point Stable node A.C. servomotor resembles Two phase induction motor Three phase induction motor Direct current series motor Universal motor Two sequences x1 (n) and x2 (n) are related by x2 (n) = x1 (- n). In the z- domain, their ROC’s are The same Reciprocal of each other Negative of each other Complements of each other 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: Absolutely integrable Absolutely summable Unity <1 The region of convergence of the z-transform of a unit step function is: |z|>1 |z|<1 (Real part of z)>0 (Real part of z)<0 Z and Laplace transform are related by: s = ln z s =ln z/T s =z s= T/ln z The scientific principle that makes hydraulic systems possible is Boyle’s law Bernoulli’s principle Pascal’s principle The fluid flow principle Proportional controller: Introduces offset Increases bandwidth Increases margin of stability Reduces velocity constant Operations performed by pneumatic controllers: Flexible operations High torque high speed operations Fire and explosion proof operation All of the mentioned Operations performed by hydraulic controllers: Flexible operations High torque high speed operations Fire and explosion proof operation All of the above The calculation in multistage process must always start from the first stage : True False Operations performed by electronic controllers: Flexible operations High torque high speed operations Fire and explosion proof operation All of the above What is the effect of phase lag compensation on the performance of a servo system? For a given relative stability, the velocity constant is increased For a given relative stability, the velocity constant is decreased The time response is made faster The bandwidth of the system is increased Fuzzy logic is : Used to respond to questions in a humanlike way A new programming language used to program animation The result of fuzzy thinking A term that indicates logical values greater than one Electrical time-constant of an armature-controlled dc servomotor is : Equal to mechanical time-constant Smaller than mechanical time-constant Larger than mechanical time-constant Not related to mechanical time-constant The unit impulse response of a system having transfer function K/(s+a) is shown below. The value of a is : t1 1/t1 1/t2 t2 The principle of invariant imbedding is : The optimal control sequence is function of initial state The optimal control sequence is function of number of stages N Control problem is imbedded with the family of problems with fixed initial value and final state The optimal control sequence is function of final state The optimal control at each state is ________ combination of states. Linear Non-linear Time variant Time invariant If a first order system and its time response to a unit step are as shown below, the gain K is : 0.25 0.8 4 2 Derivative error compensation: Improvement in transient response Reduction in steady state error Reduction is settling time Increase in damping constant In a stable control system backlash can cause which of the following? Underdamping Overdamping Poor stability at reduced values of open loop gain Low-level oscillations PD controller is used to compensate system. Compared to the uncompensated system, the compensated system has: A higher type number b) Reduced damping Reduced damping Higher noise amplification Large transient overshoot Feedback is : Linear Time variant Time invariant Non-linear P+D controller: Introduces offset Increases bandwidth Increases margin of stability Reduces velocity constant In an automatic control system which of the following elements is not used? Error detector Final control element Sensor Oscillator Signal flow graphs: They apply to linear systems The equation obtained may or may not be in the form of cause or effect Arrows are not important in the graph They cannot be converted back to block diagram Signal flow graphs are reliable to find transfer function than block diagram reduction technique. True False The type 2 system has at the origin. No net pole Net pole Simple pole Two poles In a control system integral error compensation _______ steady state error Increases Minimizes Does not have any effect on All of the above With feedback _____ reduces. System stability System gain System stability and gain All of the above Which of the following should be done to make an unstable system stable? The gain of the system should be decreased The gain of the system should be increased The number of poles to the loop transfer function should be increased The number of zeros to the loop transfer function should be increased

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