Answer / pravin kumar

uninterrupted power supply is ups.

dc to ac converter is inverters.

Answer / vineet kumar

While both provide backup power during mains outage, with
the UPS the switch is instantaneous whereas with the
Inverter there is a gap of a second or two. This gap is OK
for household gadgets such as lights, fans, fridge, etc. but
not OK for computers.

In technical terms:

UPS: The mains power comes to the UPS. The AC is converted
to DC and this DC is constantly charging the battery. The
output of the battery is fed to the Sine wave inverter and
it converts DC to AC and this feeds the equipment. Since
power out is always drawn from the battery, there is no time
lag when mains swicthes off; it justs stops the battery from
being charged and the UPS continues to supply power till the
battery runs out.

Inverter: The mains power comes to the Inverter. This is
directly sent to the output but the AC is also converted to
DC and this DC is constantly charging the battery. A sensor
and relay mechanism checks whether the mains is ON or OFF.
When the main switches OFF, the relay actuator triggers to
switch from mains to inverter. Rest is same like the UPS.
Because of this sensor and relay, there is a gap between
triggering.

UPS involves more costly circuitary and is therefor more
expensive to make and sell.

hiii,i am richa.. i want to know .. the criteria for appearung for BEL... how much percent i shuold have and is it will be for per semester or for a whole year

0 Answers   HCL,

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could u plz send me a sample placement paper for hpcl trainee engg exam..(electronics& telecommunication stream)...thnku deepikameena1@gmail.com

0 Answers   HPCL,

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What is he use of embeded systems?

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HI FRDS AM saranya i did BE (2009 PASSOUT)I PLAN TO DO DOTNET. CAN ANYBODY TELL ME WHICH TRINEE CENTRE WILL BE BEST FOR DOTNET WITH PLACEMENTS

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plz send last 5 year paper set for JE-II(ELECTRICAL)Exam held on few month in mumbai

0 Answers   RRB,

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why do we conduct the campus interviews?

4 Answers   Infosys,

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. If we have a parallel plate capacitor of plate area 'A' and plate separatoin t and having a capacity C and a metallic plate r of area A and of negligible thickness is introduced in the capacitor at a distance from either of the two plates as shown in the given figure then the capacity of the capacitor will become a.) b.) C c.) 2C d.) 4C

3 Answers   Bhel, BSNL,

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Pls send Syllabus of Jr.Eng grade2 electronics e.n.no 02/2008 & model qustions to my id amarlalmeppurath@yahoo.com

0 Answers   NSN, RK Company,

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What is parallel data transfer process?

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IN GENERAL PRACTICE HOW KVAR AND CAPACITANCE VALUE OF CAPACITOR CALCULATED?

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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

1 Answers   BSNL,

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Which two currents are relatively close in magnitude?

0 Answers  

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