Q601. Stepper motors are controlled by?
A) Frequency of pulses
B) DC voltage
C) AC voltage
D) Current amplitude
Ans: A
Explanation: The speed of a stepper motor is proportional to the frequency of input pulses.
Q602. The primary function of a servo amplifier is to?
A) Step down voltage
B) Convert AC to DC
C) Amplify control signal to drive motor
D) Store energy
Ans: C
Explanation: Servo amplifiers take low-power control signals and amplify them to power levels suitable for the motor.
Q603. A closed-loop control system in servo drives ensures?
A) Speed regulation
B) Position accuracy
C) Load variation compensation
D) All of the above
Ans: D
Explanation: Closed-loop control ensures speed, position accuracy, and load disturbance rejection.
Q604. In stepper motors, the step angle can be reduced by?
A) Increasing rotor poles
B) Decreasing rotor poles
C) Increasing stator poles
D) Both A and C
Ans: D
Explanation: A higher number of stator and rotor poles reduces the step angle.
Q605. A stepper motor takes 400 steps for one full revolution. Step angle = ?
A) 1.8°
B) 0.9°
C) 0.45°
D) 3.6°
Ans: B
Explanation: Step angle = 360° / 400 = 0.9°.
Q606. The servo motor's feedback device is used to?
A) Measure load torque
B) Provide speed or position information
C) Control voltage
D) Reduce noise
Ans: B
Explanation: Feedback devices provide real-time speed or position data to the controller.
Q607. Stepper motors are not suitable for?
A) Open-loop control
B) Precise position control
C) High-speed continuous motion
D) Low-speed control
Ans: C
Explanation: Stepper motors perform poorly at very high speeds due to loss of torque.
Q608. In a servo system, “lag error” refers to?
A) Supply delay
B) Delay between command and actual position
C) Pulse drop
D) Overvoltage
Ans: B
Explanation: Lag error is the difference between desired and actual position in servo operation.
Q609. Hybrid stepper motors combine?
A) DC and AC operation
B) Variable reluctance and permanent magnet principles
C) Series and shunt field
D) None of these
Ans: B
Explanation: Hybrid steppers combine permanent magnet and variable reluctance operation.
Q610. A stepper motor used for CNC tool positioning is preferred because?
A) Simple open-loop operation
B) High starting torque
C) Precise incremental motion
D) All of the above
Ans: D
Explanation: Stepper motors suit CNC systems for precise and repeatable step movement.
Q611. In servo systems, “gain” determines?
A) Stability
B) Speed of response
C) Output voltage
D) Frequency
Ans: B
Explanation: Increasing gain increases the response speed but may reduce stability.
Q612. The stator of a stepper motor usually has?
A) Field winding
B) Permanent magnets
C) Multiple phase windings
D) Brushes
Ans: C
Explanation: The stator has multi-phase windings energized sequentially for stepping action.
Q613. The feedback loop in servo motors helps in?
A) Power amplification
B) Correcting position errors
C) Increasing current
D) Generating frequency
Ans: B
Explanation: The feedback loop constantly corrects position/speed errors.
Q614. In stepper motors, detent torque is present when?
A) Power is on
B) Power is off
C) Motor is running
D) Motor accelerates
Ans: B
Explanation: Detent torque exists even when the motor is unpowered due to magnetic attraction.
Q615. The most precise stepper motor type is?
A) Permanent magnet
B) Variable reluctance
C) Hybrid
D) Unipolar
Ans: C
Explanation: Hybrid steppers provide high torque and fine step angles (as small as 0.9°).
Q616. A servo motor system generally consists of?
A) Motor, encoder, controller, amplifier
B) Motor and battery
C) Motor and resistor
D) Motor only
Ans: A
Explanation: Servo systems require a controller, amplifier, feedback device, and motor.
Q617. The stepping rate defines?
A) Rotor speed
B) Step frequency
C) Torque
D) Load inertia
Ans: B
Explanation: Stepping rate refers to the number of steps per second, determining motor speed.
Q618. The stability of a servo system depends on?
A) Gain margin and phase margin
B) Load torque
C) Encoder pulses
D) Step angle
Ans: A
Explanation: Gain and phase margins determine servo stability.
Q619. The motor which converts digital pulses into mechanical shaft rotation is?
A) Servo motor
B) Stepper motor
C) Induction motor
D) DC motor
Ans: B
Explanation: Stepper motors directly translate digital pulses into mechanical motion.
Q620. In a servo system, overshoot occurs when?
A) System gain is low
B) Damping is low
C) Load torque is high
D) Feedback is missing
Ans: B
Explanation: Low damping leads to overshoot in response.
Q621. The primary advantage of closed-loop stepper systems is?
A) No controller
B) Reduced noise
C) Feedback correction to prevent step loss
D) Higher voltage
Ans: C
Explanation: Closed-loop steppers prevent step loss and improve accuracy.
Q622. Stepper motors are controlled using?
A) Digital logic circuits
B) Servo amplifiers
C) Rectifiers
D) Phase splitters
Ans: A
Explanation: Stepper motors use digital logic controllers for pulse sequencing.
Q623. Servo motors are generally preferred for?
A) Static loads
B) Dynamic, varying loads
C) Constant torque loads
D) Simple drives
Ans: B
Explanation: Servo motors handle dynamic loads efficiently due to feedback control.
Q624. The servo drive’s control mode can be?
A) Torque mode
B) Speed mode
C) Position mode
D) All of the above
Ans: D
Explanation: Servo drives can operate in torque, speed, or position control modes.
Q625. Microprocessor-based controllers in stepper drives improve?
A) Efficiency
B) Resolution and smoothness
C) Cost
D) Magnetic losses
Ans: B
Explanation: Microprocessor control allows micro-stepping and smoother rotation.
Q626. The number of leads in a unipolar stepper motor?
A) 4
B) 5 or 6
C) 8
D) 3
Ans: B
Explanation: Unipolar stepper motors have 5 or 6 wires depending on configuration.
Q627. Which type of stepper motor provides maximum torque?
A) PM
B) VR
C) Hybrid
D) DC
Ans: C
Explanation: Hybrid stepper motors have high torque and precision.
Q628. The torque-speed curve of a stepper motor shows that torque?
A) Increases with speed
B) Decreases with speed
C) Remains constant
D) Randomly fluctuates
Ans: B
Explanation: Stepper motor torque decreases with increasing speed.
Q629. Servo motors are generally?
A) DC only
B) AC or DC type
C) Induction type
D) Stepper type
Ans: B
Explanation: Servo motors can be AC or DC, depending on control needs.
Q630. The main cause of step loss in steppers is?
A) Excess load or high acceleration
B) Low supply voltage
C) Too many pulses
D) High resistance
Ans: A
Explanation: Excess load or high stepping rate causes the rotor to miss steps.
Q631. The response time of a servo motor depends on?
A) Inertia and torque
B) Step angle
C) Current rating
D) Supply frequency
Ans: A
Explanation: Torque and inertia determine the acceleration and response speed.
Q632. When a servo system oscillates, it indicates?
A) Overdamping
B) Underdamping
C) Zero error
D) Perfect tuning
Ans: B
Explanation: Underdamping causes oscillations around the set point.
Q633. The encoder resolution in servo motors is measured in?
A) Degrees
B) Pulses per revolution (PPR)
C) Steps per second
D) Hertz
Ans: B
Explanation: Encoder resolution is expressed in PPR.
Q634. Stepper motor direction reversal can be done by?
A) Reversing pulse polarity
B) Changing pulse sequence
C) Changing frequency
D) Increasing voltage
Ans: B
Explanation: Changing pulse sequence reverses the rotation direction.
Q635. The servo motor error detector output is?
A) AC voltage
B) Error signal
C) Pulse train
D) Current
Ans: B
Explanation: It generates an error signal proportional to deviation from setpoint.
Q636. Stepper motor performance can be improved using?
A) Micro-stepping driver
B) Higher voltage
C) Cooling system
D) Smaller rotor
Ans: A
Explanation: Micro-stepping provides smoother, more precise operation.
Q637. The servo drive that controls speed through feedback is called?
A) Speed servo
B) Position servo
C) Torque servo
D) Open-loop drive
Ans: A
Explanation: A speed servo regulates motor velocity via feedback.
Q638. In stepper motors, torque pulsation can be reduced by?
A) Increasing load
B) Micro-stepping
C) Reducing current
D) Using a single-phase drive
Ans: B
Explanation: Micro-stepping smooths torque output by applying fractional phase currents.
Q639. Servo motors are designed for?
A) Constant speed
B) Fast acceleration/deceleration
C) High voltage operation
D) Simple loads
Ans: B
Explanation: Servo motors excel in rapid acceleration and deceleration.
Q640. The rotor in a hybrid stepper motor has?
A) Laminated teeth
B) Smooth surface
C) Salient poles
D) Slotted core
Ans: A
Explanation: Hybrid stepper rotors have laminated teeth for precision.
Q641. Stepper motor speed is proportional to?
A) Step frequency
B) Supply voltage
C) Step angle
D) Load torque
Ans: A
Explanation: Speed = (Step frequency × Step angle) / 360°.
Q642. Servo system “hunting” refers to?
A) Continuous oscillation about set point
B) Step loss
C) Load inertia
D) Drive failure
Ans: A
Explanation: Hunting occurs when the system oscillates due to improper damping.
Q643. Stepper motors are mostly used in?
A) Fans
B) CNC, robotics, printers
C) Pumps
D) Conveyor belts
Ans: B
Explanation: Stepper motors are ideal for CNCs, robotics, and printing applications.
Q644. Servo motors use feedback to control?
A) Voltage
B) Speed and position
C) Temperature
D) Current
Ans: B
Explanation: Feedback ensures precise speed and position control.
Q645. The motor producing maximum torque at standstill is?
A) Induction motor
B) Stepper motor
C) Servo motor
D) DC motor
Ans: B
Explanation: Stepper motors produce maximum torque at zero speed (holding torque).
Q646. The loop gain of a servo system determines?
A) Accuracy
B) Speed of response
C) Both A and B
D) Efficiency
Ans: C
Explanation: Higher gain improves speed and accuracy, up to the stability limit.
Q647. In stepper drives, pulse frequency determines?
A) Torque
B) Speed
C) Step size
D) Direction
Ans: B
Explanation: Speed is proportional to pulse frequency.
Q648. Servo drive fault detection is used for?
A) Thermal protection
B) Overcurrent and position error
C) Encoder signal loss
D) All of the above
Ans: D
Explanation: Servo drives include protection for thermal, overcurrent, and signal faults.
Q649. In a 1.8° stepper motor, number of steps per revolution is?
A) 100
B) 180
C) 200
D) 400
Ans: C
Explanation: Steps = 360° / 1.8° = 200 steps/rev.
Q650. In servo drives, PID control provides?
A) Position and speed accuracy
B) Power control
C) Energy storage
D) Frequency modulation
Ans: A
Explanation: PID controllers ensure accurate dynamic response and error minimization.
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