Q1. A servo motor is primarily used for
A) Constant speed operation
B) Variable speed operation
C) Position control
D) Power transmission
Answer: C
Explanation: Servo motors are used for precise control of position, speed, and acceleration in automatic control systems.
Q2. The control signal applied to a servo motor is usually a
A) DC voltage
B) Pulse-width modulated signal
C) Constant current
D) AC voltage only
Answer: B
Explanation: PWM signals control the angular position or speed in servo motors by varying the pulse width.
Q3. Stepper motor converts
A) Electrical energy into linear displacement
B) Electrical pulses into angular displacement
C) Electrical energy into mechanical vibration
D) Electrical energy into torque directly
Answer: B
Explanation: Stepper motors convert each input pulse into a fixed angular movement of the shaft.
Q4. The step angle of a stepper motor is defined as
A) Angle rotated per input voltage
B) Angle rotated per input pulse
C) Maximum rotation per cycle
D) None of these
Answer: B
Explanation: Step angle = angle through which shaft moves in response to each pulse.
Q5. A typical step angle for a 4-phase, 50-pole stepper motor is
A) 1.8°
B) 7.5°
C) 0.9°
D) 15°
Answer: A
Explanation: Step angle = 360 / (number of steps per revolution). Common stepper motors have 1.8° step angle (200 steps per revolution).
Q6. Servo motors are mostly used in
A) Pumps
B) Fans
C) Robotics
D) Compressors
Answer: C
Explanation: Due to high precision and fast response, servo motors are widely used in robotics and CNC machinery.
Q7. The speed of a stepper motor depends on
A) Supply voltage
B) Frequency of input pulses
C) Shaft load
D) Number of poles
Answer: B
Explanation: Speed ∝ frequency of pulses applied to the stator windings.
Q8. In a stepper motor, if pulse frequency increases, then speed
A) Decreases
B) Increases
C) Remains constant
D) Becomes zero
Answer: B
Explanation: Higher pulse frequency means faster step transitions, increasing speed.
Q9. The main drawback of stepper motors is
A) Complex control circuit
B) Low torque at high speed
C) High cost
D) Excessive noise
Answer: B
Explanation: Stepper motors lose torque as speed increases due to inductance and current lag.
Q10. Closed-loop control is usually associated with
A) Induction motor
B) Synchronous motor
C) Servo motor
D) DC shunt motor
Answer: C
Explanation: Servo motors work in closed-loop systems with feedback to maintain accuracy.
Q11. A stepper motor can be classified as
A) Synchronous motor
B) Induction motor
C) DC motor
D) Reluctance motor
Answer: A
Explanation: Stepper motor is a special type of synchronous motor as rotor steps are synchronized with stator magnetic field pulses.
Q12. The torque developed in a stepper motor depends on
A) Current in the stator winding
B) Voltage applied
C) Rotor inertia only
D) Supply frequency
Answer: A
Explanation: Torque is proportional to stator current and magnetic field strength.
Q13. Holding torque in a stepper motor refers to
A) Torque during rotation
B) Torque when stationary but energized
C) Torque during acceleration
D) Torque at full speed
Answer: B
Explanation: Holding torque is the torque available when the motor is energized but not rotating.
Q14. Servo motors can be
A) AC or DC type
B) Only DC type
C) Only AC type
D) Stepper type
Answer: A
Explanation: Servo motors exist in both AC and DC types, depending on the control system.
Q15. In servo systems, tachogenerators are used for
A) Speed feedback
B) Torque control
C) Voltage regulation
D) Position indication
Answer: A
Explanation: Tachogenerators produce voltage proportional to speed for feedback in servo loops.
Q16. The response of a servo motor is
A) Slow
B) Nonlinear
C) Fast
D) Constant
Answer: C
Explanation: Servo motors are designed for fast response to control signals.
Q17. A permanent magnet stepper motor has
A) Laminated rotor
B) Soft iron rotor
C) Permanent magnet rotor
D) Hybrid rotor
Answer: C
Explanation: PM stepper motor uses a permanent magnet rotor interacting with stator fields.
Q18. The hybrid stepper motor combines
A) Variable reluctance and PM types
B) DC and AC motors
C) Servo and induction motors
D) Series and shunt motors
Answer: A
Explanation: Hybrid stepper motor combines permanent magnet and variable reluctance principles.
Q19. Which of the following is NOT an advantage of stepper motor?
A) Precise positioning
B) Open-loop control
C) High speed efficiency
D) High reliability
Answer: C
Explanation: Stepper motors are inefficient at high speeds due to reduced torque.
Q20. The number of steps per revolution in a stepper motor is
A) 360 / Step angle
B) Step angle × 360
C) (Step angle / 360) × frequency
D) None of these
Answer: A
Explanation: Steps per revolution = 360 / Step angle.
Q21. The resolution of a stepper motor is improved by
A) Increasing step angle
B) Decreasing step angle
C) Increasing load
D) Increasing voltage
Answer: B
Explanation: Smaller step angle means finer control and higher resolution.
Q22. The servo motor rotor usually has
A) High inertia
B) Low inertia
C) Large diameter
D) Laminated steel core
Answer: B
Explanation: Low inertia ensures quick response to control signals.
Q23. Stepper motors are suitable for
A) Conveyor drives
B) Positioning systems
C) Fans and pumps
D) Traction drives
Answer: B
Explanation: Stepper motors are ideal for positioning and incremental motion control.
Q24. Which of the following is an open-loop system?
A) Servo motor control
B) Stepper motor drive
C) DC motor with tachogenerator
D) Automatic speed regulator
Answer: B
Explanation: Stepper motors usually work without feedback, hence open-loop.
Q25. A DC servo motor uses
A) Field control
B) Armature control
C) Both A and B
D) None of these
Answer: C
Explanation: DC servo motor control can be achieved by armature or field control methods.
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