EASA module 4 Electronic Fundamentals mcq 5

Angular displacement of the control coils with respect to the reference coils in a two phase induction motor are
a) 0o, 180o
Ans b) 90o, 270o
c) 90o, 120o
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A two phase induction motor used in a servomechanism
a) will always require a starter
Ans b) is self starting under light loads
c) runs with no slip
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A servomotor having only a tachogenerator as a feedback device will
a) vary its speed with input error voltage
Ans b) have a constant speed for any given input voltage
c) null out at a position dependant upon input error voltage
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A hysteresis servo motor is used in a servomechanism because
Ans a) it has good starting characteristics
b) good speed/voltage relationship
c) low inertia
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The null position of a torque synchro system is when
Ans a) the TX and TR rotors are parallel to each other
b) the TX and TR rotors are 90o to each other
c) the TX and TR rotors are 120o to each other
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Reversal of two of the stator connections on a torque synchro receiver would cause
a) the transmitter to become the receiver
b) the output to move the same direction as the input
Ans c) the output to move the reverse direction to the input
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An AC tachogenerator stator has
a) two windings 180o apart
b) three windings 120o apart
Ans c) two windings 90o apart
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A junction diode
Ans a) has one p-n junction
b) is similar to a vacuum diode but cannot rectify
c) can handle only very small currents
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When the rotor of an AC tachogenerator is stationary, the rotor has
a) no circulating currents
Ans b) low circulating currents
c) no magnetic fields
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The output of a tachogenerator should be
Ans a) sinusoidal
b) exponential
c) linear
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With a constant input to a speed control servo, the servo motor
a) moves to a certain position
Ans b) moves at a constant speed
c) oscillates, but otherwise does not move
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A closed loop servomechanism
a) must only have position feedback
b) must have both position and velocity feedback
Ans c) can have either position or velocity feedback
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Critical damping in a servomechanism is
a) the point which allows just one overshoot before the load comes to rest
Ans b) the amount of damping that results in the load just not oscillating
c) the critical damping required for the optimum damping of the servomechanism
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In a control synchro system the power supply is connected to the
Ans a) transmitter rotor and amplifier
b) receiver rotor and amplifier
c) transmitter and receiver rotors
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Reverse rotation of a control transformer rotor can be caused by
Ans a) connections between the transformer rotor and the amplifier reversed
b) connections to the transmitter rotor reversed
c) short circuit between two transmission lines
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Velocity feedback
Ans a) opposes the demand input
b) assists the demand input
c) prevents dead space errors
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Velocity lag can be decreased by
a) introduction of an integrator
b) keeping the error detector (summing point) output as low as possible
Ans c) decreasing the coulomb friction in the system
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The junction barrier offers opposition to only
a) holes in the p-region
b) free electrons in the n-region
Ans c) majority carriers in both regions
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An increase in velocity feedback will
Ans a) decrease the speed the load moves
b) increase the speed the load moves
c) have no effect on speed
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A two phase motor will stop when
a) the reference phase is reversed
b) the control phase is reversed
Ans c) the control phase is zero
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A tachogenerator output is
a) variable frequency, constant voltage
Ans b) variable voltage, constant frequency
c) variable frequency, variable voltage
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Rate feedback can be obtained from a
a) synchro
Ans b) tachogenerator
c) potentiometer
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Positional feedback can be obtained from a
a) synchro
b) tachogenerator
Ans c) potentiometer
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The frictional force in a servomechanism that is proportional to speed is called
a) stiction
b) coulomb friction
Ans c) viscous friction
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The 'null' point in a control synchro is when the two rotors are
Ans a) at 90o to each other
b) parallel to each other
c) wired in