Sunday, April 25, 2010 BSNL TTA EXAM Control Systems BSNL TTA EXAM Control Systems 1. An open loop control system has its (a) control action independent of the output or desired quantity (b) controlling action, depending upon human judgment (c) internal system changes automatically taken care of (d) both (a) and (b) (e) all (a),(b) and (c) 2. A servo system must have (a) feedback system (b) power amplifier to amplify error (c) capacity to control position or its derivative (d) all of these (e) none of these 3. The major disadvantage of a feedback system may be Inaccuracy (b) inefficiency (c) Unreliability (d) instability (e) Insensitivity 4. Properties of a transfer function (a) It is ratio of two polynomials is S and assumes zero initial conditions (b) It depends on system elements and not input and output of the system (c) Coefficients of the powers of S in denominator and numerator are all real constant. The order of denominator is usually greater than or equal to the order of numerator (d) All of these (e) It is a function which transfer one physical system into another physical system. 5. The classical analogous of a simple lever is (a) Capacitor bridge (b) transformer (c) mutual inductor (d) either of these 6. Two blocks G1(s) and G2(s) can be cascaded to get resultant transfer function as (a) G1(s) + G2(s) (b) G1(s) / G2(s) (c) G1(s) G2(s) (d) 1+G1(s) G2(s) (e) 1-G1(s)G2(s) (f) two blocks cannot be cascade 7. The principles of homogeneity and super position can be applied to linear time invariant system (b) non-linear time invariant system (c) digital control system (d) both (a) and (b) 8. Pick up the nonlinear system (a) automatic voltage regulator (b) d.c. servomotor with high field excitation (c) temperature control of a furnaces using thermistor (d) speed control using SCR (e) all of these 9. Signal flow graph (SFG) is a (a) polar graph (b) semi log graph (c) log log graph (d) a special type of graph for analyzing modem control system (e) a topological representation of a set of differential equations 10. Disadvantages of magnetic amplifier (a) time lag, less flexible, non-sinusoidal waveform (b) low power consumption and isolation of the active circuit (c) saturation of the core (d) all of these 11. Pick up false statement regarding magnetic amplifiers (a) The gate coil of an ideal magnetic amplifier has either zero or infinite inductance (b) Resistance of control and gate winding is very small (c) Magnetic amplifier gas dropping load characteristics (d) Magnetic amplifiers are not used to control the speed of d.c. shunt motor (e) Magnetic amplifiers can be used in automatic control of electric drivers of higher rating. 12. High power amplification is achieved by using (a) push pull amplifier (b) amplidyne (c) magnetic amplifier (d) DC amplifier (e) D.C. generator 13. Pick up false statement regarding servomotors (a) The d.c. servomotors are lighter than equivalent a.c. servomotors (b) The d.c. servomotors develops higher starting and reversing torque than equivalent a.c. servomotor. (c) A drag cup a.c. servomotor has one windings on stator and other on rotor (d) Output power of servomotors varies from 1/20 W to 100 W 14. To reduce steady state error (a) decrease natural frequency (b) decrease damping (c) increase damped frequency (d) increase time constant (f) increase gain constant of the system 15. A good factor for Mp should be (a) less than 1 (b) lying between 1.1 and 1.5 (c) more than 2.2 (d) zero (e) infinity 16. Pick up false statement. Routh-Hurwitz criterion (a) is used for determining stability of a system (b) is an algebraic procedure (c) gives the exact location of roots of the characteristic equation (d) does not indicate relative degree of stability or instability 17. Which of the following is the time domain method of determining stability of a control system (a) Bode plot (b) Nyquist plot (c) Nicholos chart (d) Routh-Hurwitz array (e) Constant M and (fy) locus (f) Root locus technique 18. The technique which gives transient response quickly as well as stability information is (a) Nyquist plot (b) Routh-Hurwitz criteria (c) Bode plot (d) Root locus plot (e) Nichols plot 19. The bandwidth can be increased by use of (a) phase lag network (b) phase lead network (c) both (a) and (b) in cascade (d) both (a) and (b) in parallel (e) none of these 20. Nyquist plot is drawn on (a) semi log graph paper (b) log log graph paper (c) polar graph paper (d) centimeter graph paper 21. If the gain margin is positive and the phase margin is negative the system is (a) stable (b) unstable (c) indeterminist 22. The Bode plot is applicable to (a) all phase network (b) minimum phase network (c) maximum phase network (d) lag lead network (e) none of these 23. The valid relation between setting time ts and rise time tr is (a) tr>ts (b) ts>tr (c) ts=tr (d) none of these 24. As a root moves further away from imaginary axis the stability (a) increases (b) decreases (c) not affected (d) none of these 25. Flat frequency response means that the magnitude ratio of output to input over the bandwidth is (a) variable (b) zero (c) constant (d) none of above 26. How many octaves are between 200 Hz and 800 Hz (a) Two octave (b) One octave (c) Four octave (d) None of above 27. Human system can be considered as (a) open loop system (b) close loop system with single feedback (c) close loop system with multivariable feedback (d) none of these 28. In a feedback system the transient response (a) Decays at constant rate (b) gets magnified (c) decays slowly (d) decays more quickly 29. Transfer function of a system is used to calculate (a) the steady state gain (b) the main constant (c) the order of system (d) the output for any given input (e) all of the above 30. Transfer function of a system is defined as the ratio of output to input in (a) Laplace transform (b) Z-transform (c) Fourier transform (d) Simple algebraic form 31. Introduction of feedback decreases the effect of (a) disturbances (b) noise signals (c) error signals (d) all the above 32. The system response of a system can be best tested with (a) unit impulse input signal (b) ramp input signal (c) sinusoidal input signal (d) exponentially decaying input signal 33. Which of the following is a closed loop system (a) electric switch (b) car starter (c) de generator (d) auto-pilot for an aircraft 34. Which of the following is used as an error detector (a) potentiometer (b) field controlled ac motor (c) amplidyne (d) armature controlled ac motor 35. The break away point of root loci are (a) open loop poles (b) closed loop poles (c) open loop zeros (d) closed loop zeros 36. Noise in a control system can be kept low by (a) reducing the bandwidth (b) attenuating such frequencies at which external signals get coupled into the system (c) both (a) and (b) (d) none of these 37. Main cause of absolute instability in the control system is (a) parameters of controlling system (b) parameters of controlled system (c) parameters of feedback system (d) error detector where the two signals are compared 38. Basically a controller is (a) a amplifier (b) a clipper (c) a comparator (d) a summer 39. A system with gain margin close to unity or a phase margin close to zero is (a) highly stable (b) highly oscillatory (c) relatively stable (d) none of these 40. Which of following elements is not used in an automatic control system (a) sensor (b) error detector (c) oscillator (d) final control element 41. AC systems are usually preferred to the DC systems in control applications because (a) AC systems are cheaper (b) AC systems are more stable (c) AC systems have better performance characteristics and smaller in size (d) all of these 42. A system has the transfer function (1-s)/(1+s); It is known as (a) low pass system (b) high pass system (c) all pass system (d) none of the above 43. In control systems, excessive bandwidth should be avoided because (a) noise is proportional to bandwidth (b) it leads to low relative stability (c) it leads to slow speed of response (d) none of these 44. In most systems, an increase in gain leads to (a) larger damping ratio (b) smaller damping ratio (c) constant damping ratio (d) none of these 45. A step function is applied to the input of a system and output is of the form y = t, the system is (a) stable (b) unstable (c) not necessarily stable (d) conditionally stable 46. Which of the following can be magnified by magnetic amplifier (a) voltage (b) current (c) power (d) none of above 47. The inductance is not used in lag network because of (a) big size (b) time delay and hysteresis losses (c) high reactance (d) none of these 48. Saturation in a stable control system can cause (a) conditional stability (b) over damping (c) low level oscillations (d) high level oscillations 49. Excessive noise in control systems can cause (a) reduction in bandwidth (b) reduction in gain (c) saturation in amplifying stages
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Question : (1) Instrument is a device for determining (a) the magnitude of a quantity (b) the physics of a variable (c) either of the above (d) both (a) and (b) (2) Electronic instruments are preferred because they have (a) no indicating part (b) low resistance in parallel circuit (c) very fast response (d) high resistance in series circuit (e) no passive elements. (3) A DC wattmeter essentially consist of (a) two ammeters (b) two voltmeters (c) a voltmeter and an ammeter (d) a current and potential transformer (4) Decibel is a unit of (a) power (b) impedance (c) frequency (d) power ratio (5) A dc voltmeter may be used directly to measure (a) frequency (b) polarity (c) power factor (d)power (6) An accurate voltmeter must have an internal impedance of (a) very low value (b) low value (c) medium value (d) very high value (7) The insulation resistance of a transformer winding can be easily measured with (a) Wheatstone bridge (b) megger (c) Kelvin bridge (d) voltmeter (8) A 100 V voltmeter has full-scale accuracy of 5%. At its reading of 50 V it will give an error of (a) 10% (b) 5% (c) 2.5% (d) 1.25% (9) You are required to check the p. f. of an electric load. No p.f. meter is available. You would use: (a) a wattmeter (b) a ammeter, a voltmeter and a wattmeter (c) a voltmeter and a ammeter (d) a kWh meter (10) The resistance of a field coil may be correctly measured by using (a) a voltmeter and an ammeter (b) Schering bridge (c) a Kelvin double bridge (d) a Maxwell bridge (11) An analog instrument has output (a) Pulsating in nature (b) Sinusoidal in nature (c) Which is continuous function of time and bears a constant relation to its input (d) Independent of the input quantity (12) Basic charge measuring instrument is (a) Duddel's oscillograph (b) Cathode ray oscillograph (c) Vibration Galvanometer (d) Bailastic Galvanometer (e) Battery Charging equipment (13) A.C. voltage can be measured (using a d.c. instrument) as a value obtained (a) by subtracting the d.c. reading from it's a.c. reading. (b) Using the output function of the multimeter (c) By using a suitable inductor in series with it (d) By using a parallel capacitor with it (e) None of the above (14) A moving coil permanent magnet ammeter can be used to measure (a) D. C. current only (b) A. C. current only (c) A. C. and D. C. currents (d) voltage by incorporating a shunt resistance (e) none of these (15) Select the wrong statement (a) the internal resistance of the voltmeter must be high (b) the internal resistance of ammeter must be low (c) the poor overload capacity is the main disadvantage of hot wires instrument (d) the check continuity with multimeter, the highest range should be used. (e) In moving iron voltmeter, frequency compensation is achieved by connecting a capacitor across its fixed coil. (16) Which of the following instrument is suitable for measuring both a.c. and d.c. quantities. (a) permanent magnet moving coil ammeter. (b) Induction type ammeter. (c) Quadrant electrometer. (d) Moving iron repulsion type ammeter. (e) Moving iron attraction type voltmeter. (17) Swamping resistance is used in moving coil instruments to reduce error due to (a) thermal EMF (b) temperature (c) power taken by the instrument (d) galvanometer sensitivity. (18) A power factor meter is based on the principle of (a) electrostatic instrument (b) Electrodynamometer instrument (c) Electro thermo type instrument (d) Rectifier type instrument. (19) A potentiometer recorder is used for (a) AC singles (b) DC signals (c) both (a) and (b) (d) time varying signals (e) none of these. (20) Transformers used in conjunction with measuring instruments for measuring purposes are called (a) Measuring transformers (b) transformer meters (c) power transformers (d) instrument transformers (e) pulse transformers. (21) Leakage flux in an electrical machine is measure by (a) Ballistic galvanometer (b) Flux meter (c) Either (a) or (b) (d) Vibration galvanometer (e) CRO (22) A C.R.O. is used to indicate (a) supply waveform (b) magnitude of the applied voltage (c) B.H. loop (d) all of these (e) Magnitude of the current flowing in it. (23) An oscillator is a (a) an amplifier having feedback network (b) a high gain amplifier (c) a wide band amplifier (d) a untuned amplifier (e) None of these (24) Distortion can be measured by (a) Wave meter (b) Digital filters (c) Wein bridge circuit (d) Bridge T filter circuit (25) Series connected Q- meter is preferable for measurement of components having (a) high impedance (b) low impedance (c) both (a) and (b) (d) high frequency (e) low capacitance (26) A potentiometer is (a) an active transducer (b) a passive transducer (c) a secondary transducer (d) a digital transducer (e) a current sensing transducer (27) The basic components of a digital voltmeter are: (a) A/D converter and a counter (b) A/D converted and a rectifier (c) D/A converter and a counter (d) Ramp generator and counter (e) Comparator (28) Which of the following electrical equipment cannot convert ac into dc (a) diode (b) converter (c) transformer (d) mercury arc rectifier (29) Voltage measurement are often taken by using either a voltmeter or (a) an ammeter (b) an ohmmeter (c) an oscillator (d) a watt-meter (30)The electric device which blocks DC but allows AC is called: (a) capacitance (b) inductor (c) an oscilloscope (d) a watt-meter (31 ) The range of an ammeter can be extended by using a (a) shunt in series (b) shunt in parallel (c) multiplier in series (d) multiplier in parallel (32)A device that changes one form of energy to another is called (a) rheostat (b) oscillator (c) transducer (d) varicap (33) Aquadag is used in CRO to collect (a) primary electron (b) secondary electron (c) both primary and secondary (d) none of above (34) A vertical amplifier for CRO can be designed for (a) only a high gain (b) only a broad bandwidth (c) a constant gain time bandwidth product (d)all of the above (35) One of the following is active transducer (a) Strain gauge (b) Selsyn (c) Photovoltic cell (d) Photo emissive cell (36) The dynamic characteristics of capacitive transducer are similar to those of (a) low pass filter (b) high pass filter (c) band pass filter (d) band stop filter (37) Thermocouples are (a) passive transducers (b) active transducers (c) both active and passive transducers (d) output transducers (38) The size of air cored transducers as compare to iron core counter part are (a) bigger (b) smaller (c) same (39) From the point of view of safety, the resistance of earthing electrode should be: (a) low (b) high (c) medium (d) the value of resistance of electrode does not effect the safety (40) In CRT the focusing anode is located (a) between pre accelerating and accelerating anodes (b) after accelerating anodes (c) before pre accelerating anodes (d) none of above (41) Which transducer converts heat energy into electrical energy (a) I. V. D. T. (b) thermocouple (c) photoconductor (d) none of the above (42) Which of photoelectric transducer is used for production of electric energy by converting solar energy (a) photo emission cell (b) photo diode (c) photo transistor (d) both (b) and (c) (43) Which of the following instruments consumes maximum power during measurement? (a) induction instruments (b) hot wire instruments (c) thermocouple instruments (d) electrodynamometer instruments (44) Which of the following meters has the best accurancy (a) moving iron meter (b) moving coil meter (c) rectifier type meter (d) thermocouple meter (45) The function of the safety resistor in ohm meter is to (a) limit the current in the coil (b) increase the voltage drop across the coil (c) increase the current in the coil (d) protect the battery (46) Which of the following instruments is free from hysteresis and eddy current losses? (a) M.l. instrument (b) electrostatic instrument (c) electrodynamometer type instrument (d)all of these (47) The dielectric loss of a capacitance can be measured by (a) Wien bridge (b) Owen bridge (c) Schering bridge (d) Maxwell bridge (48) Reed frequency meter is essentially a (a) recording system (b) deflection measuring system (c) vibration measuring system (d) oscillatory measuring system (49) In measurements made using a Q meter, high impedance elements should preferably be connected in (a) star (b) delta (c) series (d) parallel (50) A digital voltmeter measures (a) peak value (b) peak-to-peak value (c) rms value (d) average value
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