Q351. The most common feedback element used in industrial servo systems is?
A) Tachogenerator
B) Potentiometer
C) Encoder
D) Resolver
Ans: C
Explanation: Encoders provide precise digital position and speed feedback for servo systems.
Q352. In a stepper motor drive, pulse frequency controls?
A) Torque
B) Speed
C) Direction
D) Phase sequence
Ans: B
Explanation: The pulse frequency determines motor speed; faster pulses = higher speed.
Q353. A servo motor’s direction of rotation changes when?
A) Polarity of error signal reverses
B) Frequency changes
C) Supply changes
D) Load increases
Ans: A
Explanation: Reversing the polarity of the error signal reverses motor direction.
Q354. The term “slew rate” in stepper motors refers to?
A) Acceleration time
B) Maximum pulse rate before losing steps
C) Stall torque
D) Holding torque
Ans: B
Explanation: Slew rate is the highest pulse rate the stepper can follow without missing steps.
Q355. A typical servo control loop includes?
A) Only motor
B) Motor, controller, feedback
C) Motor and amplifier
D) Sensor only
Ans: B
Explanation: Servo control uses a closed-loop system of controller–amplifier–feedback–motor.
Q356. The torque developed in a DC servo motor is proportional to?
A) Field current
B) Armature current
C) Supply voltage
D) Speed
Ans: B
Explanation: Torque ∝ Armature current in DC servo motors.
Q357. Stepper motor torque decreases with?
A) Pulse frequency
B) Load
C) Voltage
D) Current
Ans: A
Explanation: Torque falls as pulse frequency (speed) increases due to inductive effects.
Q358. Servo motors are designed for?
A) Low inertia, high response
B) High inertia, low speed
C) Constant torque
D) Maximum power
Ans: A
Explanation: Low inertia allows quick acceleration/deceleration for precision control.
Q359. Stepper motors are generally driven by?
A) Phase-controlled rectifiers
B) Chopper drivers
C) Pulse train generators
D) PWM inverters
Ans: C
Explanation: Stepper drives use pulse train generators to control steps and speed.
Q360. The steady-state error in a servo system can be reduced by?
A) Increasing gain
B) Using integral control
C) Increasing damping
D) Decreasing inertia
Ans: B
Explanation: Integral control eliminates steady-state error by integrating the error over time.
Q361. The torque-speed curve of a stepper motor is called?
A) Droop curve
B) Pull-out curve
C) Pull-in curve
D) Speed characteristic
Ans: B
Explanation: The pull-out torque curve defines the limit beyond which synchronization is lost.
Q362. The AC servo motor is generally?
A) Induction type
B) DC commutator type
C) Universal type
D) Stepper type
Ans: A
Explanation: AC servo motors are two-phase induction type with special winding for control.
Q363. Stepper motor “pull-in torque” is?
A) Maximum torque without losing synchronism from rest
B) Torque at maximum speed
C) Holding torque
D) Acceleration torque
Ans: A
Explanation: Pull-in torque is the max torque to start/stop without losing steps.
Q364. Closed-loop stepper systems use?
A) Encoder feedback
B) No feedback
C) Tachometer
D) Potentiometer
Ans: A
Explanation: In closed-loop operation, encoder feedback corrects step errors dynamically.
Q365. The transfer function of a servo system relates?
A) Input voltage to current
B) Output to input
C) Torque to speed
D) Load to power
Ans: B
Explanation: Transfer function = Output/Input, representing system behavior mathematically.
Q366. The damping ratio of a servo system affects?
A) Overshoot and settling time
B) Steady-state gain
C) Torque
D) Inertia
Ans: A
Explanation: Proper damping ratio minimizes overshoot and ensures fast settling.
Q367. In a hybrid stepper motor, rotor has?
A) Teeth and permanent magnets
B) Smooth surface
C) Laminations only
D) No magnets
Ans: A
Explanation: Hybrid steppers combine teeth and PM to enhance torque and accuracy.
Q368. The control signal in a servo motor represents?
A) Desired output
B) Actual speed
C) Error feedback
D) Load torque
Ans: A
Explanation: The control signal defines the desired motion or position.
Q369. The feedback transducer in a servo system converts?
A) Electrical to mechanical
B) Mechanical to electrical
C) Thermal to mechanical
D) Electrical to magnetic
Ans: B
Explanation: Feedback transducers (like encoders) convert mechanical motion to electrical signals.
Q370. Which stepper motor type is most precise?
A) Variable reluctance
B) Permanent magnet
C) Hybrid
D) Switched reluctance
Ans: C
Explanation: Hybrid steppers have smallest step angles (0.9° or less) and best precision.
Q371. The servo motor amplifier receives input from?
A) Feedback device
B) Controller
C) Motor
D) Supply
Ans: B
Explanation: The controller sends the error-corrected signal to the amplifier.
Q372. The main difference between open-loop and closed-loop stepper systems is?
A) Speed
B) Feedback
C) Torque
D) Size
Ans: B
Explanation: Closed-loop steppers include feedback, while open-loop do not.
Q373. The purpose of acceleration control in stepper motors is to?
A) Prevent step loss
B) Increase speed
C) Reduce voltage
D) Reduce inertia
Ans: A
Explanation: Gradual acceleration avoids missed steps during start-up.
Q374. The device used for pulse generation in stepper motor drives is?
A) Timer
B) Microcontroller
C) Frequency generator
D) All of these
Ans: D
Explanation: Pulse generation can be done by timers, microcontrollers, or oscillators.
Q375. The position error in servo systems can be minimized by?
A) Increasing loop gain
B) Using integral control
C) Both A and B
D) Reducing voltage
Ans: C
Explanation: Higher gain and integral action improve precision and minimize steady-state error.
Q376. Stepper motor current control is achieved by?
A) PWM chopper
B) Linear amplifier
C) Relay circuit
D) DC supply
Ans: A
Explanation: PWM chopper drives regulate phase current for torque control.
Q377. The “pull-out torque” defines?
A) Max torque before losing synchronism
B) Minimum torque at start
C) Idle torque
D) None
Ans: A
Explanation: Pull-out torque = maximum torque where motor remains synchronized.
Q378. In servo systems, velocity feedback improves?
A) Damping
B) Accuracy
C) Gain
D) Overshoot
Ans: A
Explanation: Velocity feedback increases damping and stabilizes motion.
Q379. The response of a servo system is characterized by?
A) Rise time
B) Overshoot
C) Settling time
D) All of these
Ans: D
Explanation: System dynamics depend on all these performance parameters.
Q380. Which is not a component of a servo system?
A) Controller
B) Amplifier
C) Encoder
D) Governor
Ans: D
Explanation: Governor is mechanical speed control, not used in modern servo systems.
Q381. A typical hybrid stepper motor step angle is?
A) 3.6°
B) 1.8°
C) 5°
D) 7.5°
Ans: B
Explanation: 1.8° is standard for hybrid stepper motors (200 steps/rev).
Q382. What limits the maximum speed of a stepper motor?
A) Inductance
B) Resistance
C) Current
D) Voltage
Ans: A
Explanation: High inductance limits current rise time, thus limiting speed.
Q383. In servo tuning, proportional gain affects?
A) Response speed
B) Steady-state error
C) Overshoot
D) All of these
Ans: D
Explanation: Increasing P-gain increases speed but can cause overshoot.
Q384. Stepper motor “detent torque” is?
A) Torque without current
B) Torque with current
C) Dynamic torque
D) Pull-out torque
Ans: A
Explanation: Detent torque is due to rotor magnetism, present even when not energized.
Q385. In servo drive, the signal conditioning circuit is used for?
A) Noise filtering and scaling
B) Amplification
C) Direction control
D) Speed increase
Ans: A
Explanation: Signal conditioning ensures clean, usable feedback for control.
Q386. Stepper motor resolution increases with?
A) Smaller step angle
B) More pulses per second
C) Higher torque
D) More load
Ans: A
Explanation: Smaller step angle = finer resolution.
Q387. Which type of control is used in modern servo drives?
A) PID
B) PI only
C) P-only
D) Manual
Ans: A
Explanation: PID control provides optimal speed, accuracy, and stability.
Q388. The encoder in a servo system outputs?
A) Analog signal
B) Digital pulses
C) Sinusoidal signal
D) Current feedback
Ans: B
Explanation: Encoders provide digital pulses proportional to rotation.
Q389. Stepper motor performance deteriorates if?
A) Frequency too high
B) Load too high
C) Current too low
D) All of these
Ans: D
Explanation: Excessive load or speed or insufficient current can cause step loss.
Q390. In servo control, “bandwidth” refers to?
A) Frequency range of accurate response
B) Voltage range
C) Torque range
D) Load limit
Ans: A
Explanation: Bandwidth defines the frequency range where system tracks input accurately.
Q391. The term “hunting” in servo systems means?
A) Oscillation around setpoint
B) Loss of steps
C) Overheating
D) Sudden torque increase
Ans: A
Explanation: Hunting is a small oscillation due to poor damping.
Q392. The closed-loop gain of a servo system depends on?
A) Controller gain and feedback gain
B) Load inertia
C) Supply voltage
D) Rotor resistance
Ans: A
Explanation: Closed-loop gain = function of controller and feedback loop gains.
Q393. Microstepping drives divide each full step into?
A) Equal current levels
B) Sub-steps using sine–cosine current
C) Random pulses
D) Binary divisions
Ans: B
Explanation: Microstepping uses sine–cosine currents for smooth sub-steps.
Q394. The “settling time” in servo systems refers to?
A) Time to reach and stay near final value
B) Rise time
C) Delay time
D) Oscillation period
Ans: A
Explanation: Settling time = time until output remains within tolerance of setpoint.
Q395. The term “resolution” in encoders is measured in?
A) Volts
B) Pulses per revolution (PPR)
C) Degrees per second
D) Steps
Ans: B
Explanation: Encoder resolution = PPR, higher value → better accuracy.
Q396. In a stepper drive, “ramp control” is used to?
A) Smooth acceleration/deceleration
B) Reduce torque
C) Limit voltage
D) Adjust frequency
Ans: A
Explanation: Ramping prevents step loss by gradual acceleration/deceleration.
Q397. Servo systems are used when?
A) Position accuracy is important
B) Power is low
C) Open-loop is acceptable
D) Cost is priority
Ans: A
Explanation: Servos are preferred for high-precision motion control.
Q398. The torque constant of a servo motor represents?
A) Torque per ampere
B) Speed per volt
C) Power per second
D) Resistance
Ans: A
Explanation: Torque constant (Kt) = torque produced per ampere.
Q399. A “PID-tuned” servo system provides?
A) Fast, accurate, stable response
B) Slow response
C) Constant torque
D) No feedback
Ans: A
Explanation: PID tuning balances speed, accuracy, and damping.
Q400. Which control element compensates for system inertia?
A) Derivative
B) Integral
C) Proportional
D) None
Ans: A
Explanation: Derivative control anticipates changes, countering inertia lag.
Q401. Stepper motor holding torque increases with?
A) Current
B) Load
C) Frequency
D) Voltage drop
Ans: A
Explanation: Holding torque ∝ phase current.
Q402. The closed-loop stepper motor acts similar to?
A) Servo motor
B) DC motor
C) Universal motor
D) Induction motor
Ans: A
Explanation: Closed-loop steppers behave like servo motors with feedback.
Q403. The PWM frequency in servo drives is typically?
A) 1–5 kHz
B) 10–20 kHz
C) 50–100 Hz
D) >100 kHz
Ans: B
Explanation: Most modern servo drives use 10–20 kHz PWM for smooth control.
Q404. When feedback polarity is reversed, servo motor?
A) Oscillates violently
B) Stops
C) Runs at low speed
D) Reverses direction
Ans: A
Explanation: Wrong feedback polarity causes instability/oscillation.
Q405. The “stiffness” of a servo system is defined as?
A) Torque per unit deflection
B) Speed per torque
C) Gain per load
D) Voltage per step
Ans: A
Explanation: Stiffness = Torque / Deflection, indicating resistance to disturbance.
Q406. In microstepping, current waveform per phase is?
A) Rectangular
B) Sinusoidal
C) Triangular
D) Square
Ans: B
Explanation: Sine-cosine currents produce smooth microsteps.
Q407. Stepper motor efficiency is highest at?
A) Low speed
B) Medium speed
C) High speed
D) Zero load
Ans: B
Explanation: Efficiency peaks at medium speed range, where torque and speed balance.
Q408. Servo bandwidth should be?
A) High for fast response
B) Low for stability
C) Zero for accuracy
D) Moderate always
Ans: A
Explanation: High bandwidth enables fast, accurate response.
Q409. Stepper motor torque ripple can be minimized by?
A) Microstepping
B) High current
C) Low voltage
D) Large load
Ans: A
Explanation: Microstepping smoothens current waveform and reduces torque ripple.
Q410. Servo overshoot increases when?
A) Gain is too high
B) Damping is large
C) Integral is zero
D) Derivative is high
Ans: A
Explanation: High gain causes overshoot and possible oscillation.
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