Q26. The main function of feedback in a servo system is to
A) Amplify the input signal
B) Reduce steady-state error
C) Increase speed
D) Provide power gain
Answer: B
Explanation: Feedback in a servo system helps maintain accuracy by minimizing steady-state error between input and output.
Q27. The damping in a servo motor is provided to
A) Increase torque
B) Reduce overshoot
C) Increase speed
D) Reduce efficiency
Answer: B
Explanation: Damping prevents oscillations and ensures smooth transient response in servo systems.
Q28. The accuracy of a stepper motor depends mainly on
A) Step angle
B) Voltage rating
C) Rotor resistance
D) Shaft material
Answer: A
Explanation: Smaller step angles produce more accurate positioning.
Q29. Which of the following stepper motors offers the highest resolution?
A) Permanent magnet type
B) Variable reluctance type
C) Hybrid type
D) Any of the above
Answer: C
Explanation: Hybrid stepper motors combine features of PM and VR types, giving finer step angles and higher resolution.
Q30. The operation of a stepper motor is based on
A) Lenz’s law
B) Faraday’s law
C) Magnetic attraction and repulsion
D) Hysteresis loss
Answer: C
Explanation: Stepper motors operate by magnetic attraction and repulsion between stator and rotor magnetic fields.
Q31. Servo motors are mainly designed for
A) High torque, low speed
B) High power applications
C) Low torque, high precision
D) Low power factor
Answer: C
Explanation: Servo motors prioritize accuracy and responsiveness over torque capacity.
Q32. The frequency of input pulses in a stepper motor controls
A) Torque
B) Speed
C) Current
D) Load angle
Answer: B
Explanation: Frequency of pulses determines how many steps per second occur, hence controlling speed.
Q33. The maximum torque a stepper motor can produce without losing synchronism is called
A) Holding torque
B) Detent torque
C) Pull-out torque
D) Pull-in torque
Answer: C
Explanation: Pull-out torque is the maximum torque at which the motor can remain synchronized with the input pulses.
Q34. Detent torque in a stepper motor is
A) Torque when the motor is off
B) Torque when the motor is at high speed
C) Torque during acceleration
D) None of the above
Answer: A
Explanation: Detent torque is the torque required to move the rotor from its rest position when unenergized.
Q35. The AC servo motor is basically a
A) Induction motor
B) Synchronous motor
C) Universal motor
D) Stepper motor
Answer: A
Explanation: AC servo motor is a modified two-phase induction motor with low rotor inertia and high starting torque.
Q36. In a DC servo motor, the control signal is applied to
A) Field circuit
B) Armature circuit
C) Both field and armature
D) Shaft position sensor
Answer: B
Explanation: Armature voltage is varied to control speed and torque in DC servo motors.
Q37. Stepper motors are most commonly used in
A) Elevators
B) Printers and CNC machines
C) Pumps
D) Fans
Answer: B
Explanation: Stepper motors provide precise position control required in printers and CNC machines.
Q38. The direction of rotation of a stepper motor depends on
A) Pulse amplitude
B) Pulse frequency
C) Pulse sequence
D) Pulse width
Answer: C
Explanation: Changing the phase sequence of input pulses reverses the rotation direction.
Q39. The control system used in a stepper motor drive is usually
A) Digital
B) Analog
C) Mechanical
D) Hydraulic
Answer: A
Explanation: Stepper motors are digitally controlled using pulse trains from microcontrollers or computers.
Q40. Which one of the following is NOT a type of stepper motor?
A) Variable reluctance
B) Permanent magnet
C) Hybrid
D) Induction type
Answer: D
Explanation: Induction motor is not a type of stepper motor.
Q41. A hybrid stepper motor typically has a step angle of
A) 7.5°
B) 1.8°
C) 0.5°
D) 15°
Answer: B
Explanation: Hybrid stepper motors commonly have a step angle of 1.8°, offering 200 steps per revolution.
Q42. The torque developed in a stepper motor decreases when
A) Step rate increases
B) Step rate decreases
C) Supply voltage increases
D) Load decreases
Answer: A
Explanation: At higher stepping rates, current cannot fully build up due to inductance, reducing torque.
Q43. In a servo motor, the feedback device is usually a
A) Resistor
B) Encoder or potentiometer
C) Relay
D) Rectifier
Answer: B
Explanation: Encoders or potentiometers provide position or speed feedback for control systems.
Q44. Which of the following statements is true for servo motors?
A) They operate without feedback
B) They are constant speed devices
C) They are used in closed-loop systems
D) They cannot be reversed
Answer: C
Explanation: Servo motors always operate in closed-loop systems for accurate control.
Q45. The pulse rate required to rotate a stepper motor at 600 rpm with 200 steps/rev is
A) 1000 pulses/sec
B) 2000 pulses/sec
C) 3000 pulses/sec
D) 4000 pulses/sec
Answer: B
Explanation:
Speed = (Pulse rate × 60) / Steps per revolution
→ Pulse rate = (600 × 200) / 60 = 2000 pulses/sec.
Q46. The main advantage of stepper motors over DC motors is
A) Higher efficiency
B) Simpler mechanical construction
C) Precise position control without feedback
D) Higher torque
Answer: C
Explanation: Stepper motors can achieve precise position control in open-loop configuration.
Q47. In a servo system, error detector compares
A) Input and output signals
B) Voltage and current
C) Torque and speed
D) None of the above
Answer: A
Explanation: The error detector finds the difference between desired (input) and actual (feedback) outputs.
Q48. The most common feedback element used in servo systems is
A) Thermistor
B) Potentiometer
C) Transistor
D) SCR
Answer: B
Explanation: Potentiometers provide simple and continuous feedback proportional to position.
Q49. The open-loop transfer function of a servo system determines
A) Stability
B) Accuracy
C) Damping
D) Gain
Answer: A
Explanation: Stability of the servo system depends on the poles of the open-loop transfer function.
Q50. Stepper motors are preferred in applications where
A) Smooth continuous motion is required
B) High acceleration and deceleration are needed
C) Precise and repeatable movement is required
D) Large power is required
Answer: C
Explanation: Stepper motors are ideal for precise, incremental, and repeatable motion such as in robotics, CNC, and automation.
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