Q.1 What is the primary function of a servo drive?
To regulate AC voltage
To control the position, velocity, or torque of a servo motor
To amplify signals
To convert DC to AC
Explanation - A servo drive receives a command signal and generates the necessary power to move a servo motor to a desired position, speed, or torque. It is not merely a voltage regulator or amplifier.
Correct answer is: To control the position, velocity, or torque of a servo motor
Q.2 Which component of a servo drive provides the power conversion from DC to the motor’s required voltage?
PWM controller
DC-DC converter
Inverter
Gate driver
Explanation - An inverter in a servo drive converts DC from the supply to AC (or PWM-modulated DC) that drives the motor. The PWM controller shapes the signal, and the gate driver drives the switching devices.
Correct answer is: Inverter
Q.3 In a closed‑loop servo system, what is the role of the encoder?
To supply power
To measure the motor shaft position
To provide cooling
To act as a fuse
Explanation - An encoder generates signals proportional to the shaft position (or speed), which are compared to the desired set‑point in the feedback loop.
Correct answer is: To measure the motor shaft position
Q.4 Which control algorithm is most commonly used in high‑performance servo drives?
Proportional (P) control
PID (Proportional‑Integral‑Derivative) control
On‑off control
Feed‑forward only control
Explanation - PID control combines proportional, integral, and derivative actions to achieve accurate tracking and reject disturbances in servo systems.
Correct answer is: PID (Proportional‑Integral‑Derivative) control
Q.5 Which of the following is NOT a typical application of servo drives?
Robotic arm joints
CNC machine spindles
HVAC dampers
Linear conveyor belts
Explanation - HVAC dampers use pneumatic or simple electric actuators, not precision servo drives. The other options require precise motion control.
Correct answer is: HVAC dampers
Q.6 What does PWM stand for in the context of servo drives?
Power Management Wave
Pulse‑Width Modulation
Programmable Motor Wave
Phase‑Weighted Modulator
Explanation - PWM is a technique that controls the average voltage delivered to the motor by switching the supply on and off rapidly with varying duty cycles.
Correct answer is: Pulse‑Width Modulation
Q.7 Which of the following statements about brushless DC motors (BLDC) is true?
They use brushes to commutate the current
They are typically used in low‑speed applications
They require a commutator
They are controlled using electronic commutation
Explanation - BLDC motors eliminate brushes and commutators by using electronic control to switch the phases.
Correct answer is: They are controlled using electronic commutation
Q.8 In a servo drive, what is the primary purpose of the current sense resistor?
To detect motor temperature
To provide a voltage reference
To measure the motor current for protection and control
To filter noise from the power supply
Explanation - The current sense resistor drops a small voltage proportional to the motor current, which is used for over‑current protection and feedback to the drive.
Correct answer is: To measure the motor current for protection and control
Q.9 Which term describes the maximum torque that a servo drive can provide without stalling?
Holding torque
Peak torque
Rated torque
Stall torque
Explanation - Peak torque is the maximum torque achievable during operation. Holding torque is the torque required to maintain a position.
Correct answer is: Peak torque
Q.10 Which feedback device can provide both position and velocity information in a single sensor?
Hall‑effect sensor
Optical encoder
Potentiometer
Magnetic tachometer
Explanation - An optical encoder can generate pulses for position and by counting pulses over time, velocity can be derived.
Correct answer is: Optical encoder
Q.11 What is the main advantage of using a digital servo drive over an analog drive?
Higher speed
Simpler wiring
More precise control and programmability
Lower cost
Explanation - Digital drives use microprocessors and firmware that can implement advanced algorithms, diagnostics, and remote configuration.
Correct answer is: More precise control and programmability
Q.12 In a servo drive’s closed‑loop control, what does the error signal represent?
The difference between desired and actual torque
The difference between desired and actual speed
The difference between desired and actual position
All of the above
Explanation - The error can be formulated in terms of position, velocity, or torque depending on the application, but it always represents the discrepancy between set‑point and measurement.
Correct answer is: All of the above
Q.13 Which type of motor is most commonly used in high‑precision industrial servo applications?
Synchronous reluctance motor
Induction motor
Brushless DC motor
Universal motor
Explanation - BLDC motors offer high torque‑to‑weight ratio, excellent speed regulation, and are widely used in precision drives.
Correct answer is: Brushless DC motor
Q.14 What is the role of the torque controller in a servo drive?
To convert torque to voltage
To adjust the duty cycle to achieve desired torque
To limit the current
To generate the motor shaft position signal
Explanation - The torque controller modulates the PWM duty cycle based on the torque command and current feedback to produce the required torque.
Correct answer is: To adjust the duty cycle to achieve desired torque
Q.15 Which of these is NOT typically a feature of a modern servo drive’s diagnostic system?
Motor temperature monitoring
Over‑current protection
Homing routine
External fuse
Explanation - Diagnostics involve monitoring conditions; an external fuse is a protection device, not a diagnostic feature.
Correct answer is: External fuse
Q.16 How does a velocity‑mode controller differ from a position‑mode controller?
Velocity mode uses a proportional controller only
Position mode directly commands motor current
Velocity mode uses a speed error signal, position mode uses a position error signal
They are the same, just different names
Explanation - Velocity mode controls speed error; position mode controls the difference between desired and actual positions.
Correct answer is: Velocity mode uses a speed error signal, position mode uses a position error signal
Q.17 What is the typical maximum switching frequency for a 4‑phase brushless DC servo drive?
1 kHz
10 kHz
20 kHz
50 kHz
Explanation - High‑performance drives often use switching frequencies around 10–20 kHz to minimize ripple while maintaining efficient operation.
Correct answer is: 20 kHz
Q.18 Which of the following is a key advantage of using a PID controller in servo drives?
It eliminates the need for sensors
It guarantees zero steady‑state error
It reduces overshoot and improves stability
It requires no tuning
Explanation - PID tuning helps balance responsiveness and stability, reducing overshoot and settling time.
Correct answer is: It reduces overshoot and improves stability
Q.19 What is the purpose of the feed‑forward term in a servo control loop?
To compensate for expected disturbances
To reduce the integral action
To filter the sensor noise
To provide a safety shutdown
Explanation - Feed‑forward uses known input data (e.g., load torque) to anticipate changes and adjust the command before the feedback loop reacts.
Correct answer is: To compensate for expected disturbances
Q.20 Which type of encoder is typically used in high‑resolution servo drives?
Incremental encoder
Quadrature encoder
Absolute encoder
Resistive encoder
Explanation - Absolute encoders provide unique position values even after power loss, which is critical for high‑precision applications.
Correct answer is: Absolute encoder
Q.21 In a servo drive, what is the function of the current regulator loop?
To maintain motor speed
To adjust the PWM duty cycle based on current measurement
To regulate temperature
To set the torque reference
Explanation - The current regulator ensures the actual motor current follows the commanded current, providing torque control.
Correct answer is: To adjust the PWM duty cycle based on current measurement
Q.22 Which of the following is an example of a torque‑controlled servo system?
An elevator positioning system
A robotic joint driven by a constant current drive
A DC motor running at a fixed speed
A servo motor with open‑loop speed control
Explanation - Torque control is achieved by regulating the current, which directly relates to torque in a motor.
Correct answer is: A robotic joint driven by a constant current drive
Q.23 What is the primary benefit of using a multi‑phase servo motor?
Simpler wiring
Higher torque ripple
Reduced harmonic content and smoother torque
Lower cost
Explanation - Multi‑phase motors distribute torque over multiple windings, reducing ripple and improving motion quality.
Correct answer is: Reduced harmonic content and smoother torque
Q.24 Which of the following best describes a closed‑loop control system?
It uses an input without any feedback
It uses feedback to correct errors
It is only used in analog drives
It requires no sensors
Explanation - Closed‑loop systems compare the output to the desired set‑point and adjust the input to reduce error.
Correct answer is: It uses feedback to correct errors
Q.25 What does the term ‘back‑EMF’ refer to in the context of motor drives?
The electrical noise generated by the drive
The voltage induced in the motor winding due to its rotation
The voltage drop across the current sense resistor
The supply voltage to the drive
Explanation - Back‑EMF is the electromotive force that opposes the applied voltage and depends on rotor speed.
Correct answer is: The voltage induced in the motor winding due to its rotation
Q.26 Which control variable is most directly proportional to the current flowing through a motor?
Speed
Torque
Position
Voltage
Explanation - In most motors, especially BLDC and synchronous motors, torque is directly proportional to current.
Correct answer is: Torque
Q.27 Why are MOSFETs often used as the switching devices in servo drives?
They have high on‑resistance
They support high switching frequencies with low losses
They are inexpensive
They do not require gate drivers
Explanation - MOSFETs provide fast switching and low conduction losses, making them ideal for PWM drives.
Correct answer is: They support high switching frequencies with low losses
Q.28 What is the main purpose of a 'homing' routine in servo control?
To calibrate the current sensor
To bring the motor to a known reference position
To turn off the motor
To set the maximum speed
Explanation - Homing ensures that the drive knows its exact zero position before starting precise operations.
Correct answer is: To bring the motor to a known reference position
Q.29 Which type of sensor is used to detect magnetic field changes for motor position feedback?
Hall‑effect sensor
Temperature sensor
Pressure sensor
Capacitive sensor
Explanation - Hall sensors detect magnetic fields and can be used for incremental or absolute position feedback.
Correct answer is: Hall‑effect sensor
Q.30 What is the typical maximum torque ripple for a 3‑phase brushless DC motor?
1–2 %
5–10 %
15–20 %
25–30 %
Explanation - Well‑designed 3‑phase BLDC motors aim for torque ripple in the single‑digit percentage range for smooth operation.
Correct answer is: 5–10 %
Q.31 Which of these is a safety feature commonly included in servo drives?
Current limiting
Speed ramping
Thermal shutdown
All of the above
Explanation - Servo drives integrate multiple safety mechanisms to protect the motor, the drive, and the operator.
Correct answer is: All of the above
Q.32 What is the main advantage of using a field‑weakening technique in high‑speed servo drives?
Higher torque at low speeds
Reduced current consumption
Extended speed range beyond base speed
Lower EMI
Explanation - Field‑weakening reduces flux to allow the motor to run faster than its base speed.
Correct answer is: Extended speed range beyond base speed
Q.33 What is the function of the 'damping' term in a PID controller?
To reduce overshoot by adding a derivative term
To increase steady‑state error
To correct for sensor bias
To set the maximum output
Explanation - The derivative action provides a damping effect that opposes rapid changes in error, reducing overshoot.
Correct answer is: To reduce overshoot by adding a derivative term
Q.34 Which of the following is a common application for servo drives in the aerospace industry?
Aircraft landing gear actuation
Engine oil pump control
Avionics display cooling
Fuel cell power supply
Explanation - Landing gear requires precise, repeatable motion, making servo drives suitable for the application.
Correct answer is: Aircraft landing gear actuation
Q.35 What does 'regulation' refer to in servo drive terminology?
The speed at which the drive can respond to changes
The ability to maintain a constant torque under varying load
The precision of position control
All of the above
Explanation - Regulation encompasses speed, torque, and position accuracy in the context of servo performance.
Correct answer is: All of the above
Q.36 Which of these parameters is NOT directly influenced by the PWM duty cycle?
Motor voltage
Motor speed
Motor current
Motor temperature
Explanation - While PWM duty affects motor current and thus temperature indirectly, temperature is a consequence, not a direct parameter.
Correct answer is: Motor temperature
Q.37 In servo drives, what is the purpose of the 'dead time' in the gate driver?
To allow the motor to cool
To prevent shoot‑through during switching
To increase switching frequency
To synchronize with the encoder
Explanation - Dead time ensures that both high‑side and low‑side switches are off simultaneously to avoid short circuits.
Correct answer is: To prevent shoot‑through during switching
Q.38 Which of these is a typical limitation of open‑loop servo systems?
High precision
Robustness to disturbances
Limited ability to correct errors
Easy tuning
Explanation - Open‑loop systems lack feedback, making them susceptible to load changes and inaccuracies.
Correct answer is: Limited ability to correct errors
Q.39 What is the main reason for using a 'soft start' in servo drives?
To reduce mechanical shock
To increase motor speed instantly
To eliminate the need for a controller
To improve the drive’s temperature profile
Explanation - Soft start gradually ramps up current, reducing sudden torque spikes that could damage components.
Correct answer is: To reduce mechanical shock
Q.40 Which of the following best describes the relationship between motor speed and back‑EMF?
Back‑EMF increases with speed
Back‑EMF decreases with speed
Back‑EMF is independent of speed
Back‑EMF only depends on current
Explanation - Back‑EMF is proportional to rotor speed and magnetic flux.
Correct answer is: Back‑EMF increases with speed
Q.41 In a servo drive, what does the 'torque‑current' relationship represent?
The conversion of voltage to speed
The proportionality between current and generated torque
The relationship between speed and voltage
The dependency of position on current
Explanation - In many DC and synchronous motors, torque is directly proportional to armature current.
Correct answer is: The proportionality between current and generated torque
Q.42 Which of these is a typical signal used for servo drive communication in industrial networks?
RS‑232
CANopen
USB
Ethernet/IP
Explanation - CANopen is widely used in servo networks due to its deterministic, real‑time communication.
Correct answer is: CANopen
Q.43 What is the effect of increasing the PWM switching frequency in a servo drive?
Increases ripple in the output voltage
Reduces switching losses
Improves torque ripple and dynamic response
Has no effect
Explanation - Higher switching frequencies reduce ripple and allow faster control action, improving dynamic performance.
Correct answer is: Improves torque ripple and dynamic response
Q.44 Which component in a servo drive is responsible for filtering high‑frequency noise from the power supply?
Inductor
Capacitor
Diode
Resistor
Explanation - Capacitors act as local reservoirs to smooth voltage spikes and filter high‑frequency noise.
Correct answer is: Capacitor
Q.45 Which of the following is an advantage of using an absolute encoder over an incremental encoder?
Lower cost
Higher resolution
No need to perform a homing routine
Simpler wiring
Explanation - Absolute encoders provide a unique position code even after power loss, eliminating the need for homing.
Correct answer is: No need to perform a homing routine
Q.46 What does the term 'over‑current protection' in servo drives entail?
Preventing the drive from drawing too much current from the supply
Limiting the maximum torque output
Ensuring the motor runs at a fixed speed
All of the above
Explanation - Over‑current protection monitors current and limits it to safe levels to protect components.
Correct answer is: Preventing the drive from drawing too much current from the supply
Q.47 Which type of servo motor is best suited for high‑temperature applications?
Alkaline‑cell motor
Brushless DC motor with heat‑resistant insulation
Synchronous reluctance motor
Universal motor
Explanation - BLDC motors can be designed with high‑temperature insulation, making them suitable for harsh environments.
Correct answer is: Brushless DC motor with heat‑resistant insulation
Q.48 What is 'hysteresis' in the context of servo control?
The lag between input and output signals
The tendency of a system to resist changes in motion
The difference between maximum and minimum torque
The time delay in sensor response
Explanation - Hysteresis refers to the lagging behavior of magnetic or mechanical components when changing state.
Correct answer is: The tendency of a system to resist changes in motion
Q.49 Which of these is a common method to reduce motor vibration in servo systems?
Using a higher resolution encoder
Adding mechanical dampers
Increasing the switching frequency
All of the above
Explanation - Each technique contributes to reducing vibration and improving motion quality.
Correct answer is: All of the above
Q.50 What is the purpose of the 'dead‑band' in a servo feedback loop?
To allow small position errors without generating control action
To increase the speed of the motor
To reduce power consumption
To provide safety shut‑down
Explanation - A dead‑band prevents the controller from reacting to noise or minor deviations, improving stability.
Correct answer is: To allow small position errors without generating control action
Q.51 Which of the following describes the 'torque constant' of a motor?
The maximum torque the motor can produce
The ratio of torque to current
The ratio of speed to voltage
The torque generated at zero current
Explanation - The torque constant (K_t) relates the armature current to the generated torque.
Correct answer is: The ratio of torque to current
Q.52 In servo drive terminology, what does 'open‑loop' control mean?
Using feedback to adjust the motor command
Driving the motor with no feedback, purely based on the input command
Using a PID controller
Using a proportional controller only
Explanation - Open‑loop control does not use sensor feedback; the motor is driven purely by the command signal.
Correct answer is: Driving the motor with no feedback, purely based on the input command
Q.53 Which parameter is typically specified in a servo drive datasheet to indicate the maximum operating speed?
Rated speed
Maximum speed
Base speed
Speed range
Explanation - The maximum speed indicates the highest speed the drive can reliably achieve under rated conditions.
Correct answer is: Maximum speed
Q.54 Which of these is a key feature of a 'vector control' technique?
Decoupling torque and flux control
Using only the motor speed for control
Ignoring the motor’s magnetic field
All of the above
Explanation - Vector control separates torque and flux, allowing precise control of both independent of each other.
Correct answer is: Decoupling torque and flux control
Q.55 What is the primary benefit of using a high‑resolution incremental encoder in a servo drive?
Lower cost
Higher speed tolerance
Finer position resolution
Simpler installation
Explanation - High‑resolution encoders provide more counts per revolution, enabling finer position measurement.
Correct answer is: Finer position resolution
Q.56 Which of the following best describes the 'dead zone' in a servo controller?
A region where the controller output is zero regardless of error
The time it takes for the controller to respond
The maximum torque the motor can produce
The region where the motor cannot move
Explanation - Dead zones prevent the controller from reacting to small errors or noise, improving stability.
Correct answer is: A region where the controller output is zero regardless of error
Q.57 Which of these is NOT a common method of current sensing in servo drives?
Shunt resistor
Hall‑effect sensor
Current transformer
Voltage divider
Explanation - Voltage dividers do not accurately sense current; shunt resistors, Hall sensors, and transformers are used.
Correct answer is: Voltage divider
Q.58 Why is 'thermal protection' critical in servo drives?
To avoid overheating of motor windings
To reduce electromagnetic interference
To increase mechanical vibration
To improve power factor
Explanation - Excessive heat can damage insulation and reduce the lifespan of motor windings.
Correct answer is: To avoid overheating of motor windings
Q.59 Which of the following best describes a 'vector motor' in the context of servo drives?
A motor that uses vector addition for motion
A motor that has separate torque and flux control axes
A motor that uses magnetic vectors for propulsion
An inverter that produces a vector signal
Explanation - Vector motors allow independent control of torque and flux components, improving performance.
Correct answer is: A motor that has separate torque and flux control axes
Q.60 What is a typical purpose of the 'speed ramp' feature in servo drives?
To gradually increase or decrease speed
To maintain constant speed at all times
To reduce noise
To eliminate torque ripple
Explanation - Speed ramps help prevent sudden changes that could cause mechanical stress or electrical transients.
Correct answer is: To gradually increase or decrease speed
Q.61 Which of these is a key difference between a 'servo motor' and a 'stepper motor'?
Servo motors are always DC
Stepper motors are open‑loop
Servo motors provide continuous motion, stepper motors provide discrete steps
Step motors use feedback, servo motors do not
Explanation - Servo motors can produce smooth, continuous motion, while stepper motors move in discrete steps.
Correct answer is: Servo motors provide continuous motion, stepper motors provide discrete steps
Q.62 In a servo drive, which loop typically operates at the highest speed?
Current control loop
Speed control loop
Position control loop
Torque control loop
Explanation - The current loop is usually the fastest to respond to changes, often at the PWM switching frequency.
Correct answer is: Current control loop
Q.63 Which component of a servo drive helps to mitigate electromagnetic interference (EMI) in high‑frequency operation?
Gate driver isolation
Ferrite chokes
Large inductors
All of the above
Explanation - Isolation, ferrite chokes, and inductors all contribute to reducing EMI.
Correct answer is: All of the above
Q.64 What does the 'motor phase angle' represent in a 3‑phase motor?
The electrical angle between motor phases
The mechanical angle of the shaft
The angular position of the encoder
The phase shift introduced by the drive
Explanation - Motor phase angle refers to the relative phase difference between the electrical currents in the three phases.
Correct answer is: The electrical angle between motor phases
Q.65 Which of the following is a typical application of servo drives in automotive industry?
Airbag deployment
Engine cooling fans
Steering column actuation
Fuel injection timing
Explanation - Servo drives enable precise, variable‑torque steering systems in modern vehicles.
Correct answer is: Steering column actuation
Q.66 What is the role of the 'soft‑start' function in a servo drive?
To increase the starting torque
To limit the initial current surge
To maintain constant speed
To prevent the drive from overheating
Explanation - Soft‑start gradually ramps current to reduce mechanical shock and electrical spikes.
Correct answer is: To limit the initial current surge
Q.67 What does 'over‑temperature protection' in a servo drive do?
Shuts down the drive when temperature exceeds limits
Increases cooling fan speed
Reduces torque output
All of the above
Explanation - The drive monitors temperature and will shut down to prevent damage when a threshold is crossed.
Correct answer is: Shuts down the drive when temperature exceeds limits
Q.68 Which of the following is NOT typically included in the 'drive firmware' of a servo system?
Control algorithms
Communication protocols
Mechanical design details
Diagnostics routines
Explanation - Firmware contains software logic, not mechanical specifications.
Correct answer is: Mechanical design details
Q.69 Which parameter is critical for determining the efficiency of a servo drive?
Motor winding resistance
Switching frequency
Control algorithm
All of the above
Explanation - Resistance causes copper loss, high switching frequency increases switching loss, and control algorithm affects energy usage.
Correct answer is: All of the above
Q.70 What is the main purpose of a 'current‑sense amplifier' in a servo drive?
To amplify the motor voltage
To provide a high‑gain, low‑offset measurement of motor current
To convert AC to DC
To filter sensor noise
Explanation - The amplifier ensures accurate current measurement for the current regulator.
Correct answer is: To provide a high‑gain, low‑offset measurement of motor current
Q.71 In servo drive terminology, what is a 'dead‑time' compensation?
Compensating for the time when the motor is idle
Adjusting the gate driver to prevent overlap of switching devices
Adding a delay to the control signal
None of the above
Explanation - Dead‑time compensation ensures that high‑side and low‑side switches are off simultaneously.
Correct answer is: Adjusting the gate driver to prevent overlap of switching devices
Q.72 Which of the following is a typical measure to improve the electromagnetic compatibility (EMC) of a servo drive?
Using shielding
Adding ferrite beads
Increasing the switching frequency
Using larger inductors
Explanation - Ferrite beads suppress high‑frequency noise, improving EMC.
Correct answer is: Adding ferrite beads
Q.73 Which of the following is a characteristic of a 'dual‑mode' servo drive?
It can operate in both AC and DC modes
It can switch between position and torque control
It uses two separate power supplies
All of the above
Explanation - Dual‑mode drives allow switching between different control schemes as needed.
Correct answer is: It can switch between position and torque control
Q.74 What does the term 'efficiency' refer to in a servo drive context?
The ratio of output torque to input power
The ratio of output speed to input speed
The ratio of input voltage to output voltage
The ratio of output current to input current
Explanation - Efficiency measures how effectively electrical energy is converted to mechanical work.
Correct answer is: The ratio of output torque to input power
Q.75 Which of the following is a common failure mode in servo drives?
Over‑temperature shutdown
Phase loss due to capacitor failure
Inverter overload
All of the above
Explanation - Multiple failure modes can occur in servo drives due to various component failures.
Correct answer is: All of the above
Q.76 What is the main advantage of using a 'sensorless' control technique in servo drives?
Reduced cost by eliminating sensors
Higher accuracy
Faster response
Simpler wiring
Explanation - Sensorless drives estimate rotor position from motor signals, reducing sensor costs.
Correct answer is: Reduced cost by eliminating sensors
Q.77 Which of the following describes 'torque ripple' in a servo motor?
Oscillation of torque during constant speed operation
The difference between maximum and minimum speed
The variation in voltage supply
The error in position measurement
Explanation - Torque ripple is the periodic variation of torque that can cause vibration.
Correct answer is: Oscillation of torque during constant speed operation
Q.78 What is the main function of the 'phase‑locked loop (PLL)' in a servo drive?
To synchronize the drive’s internal clock with the motor’s electrical cycle
To control the motor’s torque directly
To convert AC to DC
To monitor the motor temperature
Explanation - The PLL aligns the controller’s timing to the motor’s electrical frequency for precise control.
Correct answer is: To synchronize the drive’s internal clock with the motor’s electrical cycle
Q.79 Which of the following is a benefit of using a 'digital torque sensor' in servo drives?
Higher measurement accuracy
Simplified wiring
Lower cost
All of the above
Explanation - Digital torque sensors provide precise torque measurement, improving control quality.
Correct answer is: Higher measurement accuracy
Q.80 What does 'motor flux weakening' achieve in high‑speed servo operation?
Increase the torque
Decrease the torque to allow higher speeds
Increase the back‑EMF
Decrease the back‑EMF
Explanation - Flux weakening reduces magnetic flux, lowering torque but permitting speeds beyond base speed.
Correct answer is: Decrease the torque to allow higher speeds
Q.81 Which of the following best describes the 'closed‑loop velocity control' in a servo drive?
The drive adjusts motor voltage to match a desired speed set‑point
The drive uses only a position sensor to control speed
The drive operates without any feedback
The drive adjusts the load to maintain speed
Explanation - Closed‑loop velocity control uses speed feedback to adjust power delivery to maintain the target speed.
Correct answer is: The drive adjusts motor voltage to match a desired speed set‑point
Q.82 What is the typical purpose of the 'limit switch' in a servo system?
To restrict the maximum torque
To provide a hard stop for motion
To monitor the motor temperature
To detect the motor’s speed
Explanation - Limit switches physically stop the motor from exceeding its mechanical travel limits.
Correct answer is: To provide a hard stop for motion
Q.83 Which of the following is a common cause of 'stiction' in servo motor systems?
Low motor torque
High friction in mechanical joints
High switching frequency
Low resolution encoder
Explanation - Stiction, or static friction, occurs when joints resist initial motion due to friction.
Correct answer is: High friction in mechanical joints
Q.84 In servo control, what is the difference between 'direct drive' and 'indirect drive' configurations?
Direct drive uses a gear box, indirect does not
Direct drive connects the motor directly to the load, indirect uses an intermediate gear or belt
Direct drive uses a DC motor, indirect uses an AC motor
There is no difference
Explanation - Direct drives eliminate gearboxes for higher precision, while indirect drives use gearboxes for torque multiplication.
Correct answer is: Direct drive connects the motor directly to the load, indirect uses an intermediate gear or belt
Q.85 What is the main advantage of using a 'Hall‑sensor' over a 'quadrature encoder' for speed measurement?
Higher resolution
Simplicity and robustness
Ability to provide absolute position
Lower cost
Explanation - Hall sensors are simple and robust for speed measurement but lack high resolution.
Correct answer is: Simplicity and robustness
Q.86 Which of the following is a typical parameter that a servo drive may report for diagnostic purposes?
Motor temperature
Supply voltage
Current consumption
All of the above
Explanation - Diagnostics often include temperature, voltage, current, and error codes.
Correct answer is: All of the above
Q.87 What is the function of the 'motor phase control' in a three‑phase servo drive?
To adjust the phase sequence for speed control
To reduce the back‑EMF
To increase the motor's power factor
All of the above
Explanation - Phase control changes the timing of phase currents to adjust speed and torque.
Correct answer is: To adjust the phase sequence for speed control
Q.88 Which of these is an advantage of using a 'gearless' servo motor?
Higher torque density
Lower precision
Simpler mechanical design
Higher maintenance requirements
Explanation - Gearless motors provide high torque per weight without the loss and backlash of gears.
Correct answer is: Higher torque density
Q.89 Which of the following best describes the 'feedback loop bandwidth' in a servo system?
The speed at which the motor can be accelerated
The rate at which the feedback signal can change without causing instability
The maximum speed of the motor
The minimum torque output
Explanation - Bandwidth indicates how quickly the controller can respond to changes in the feedback signal.
Correct answer is: The rate at which the feedback signal can change without causing instability
Q.90 What is the primary function of a 'sine‑wave inverter' in a servo drive?
To produce a DC output from AC input
To generate a sine‑wave AC voltage for AC motors
To regulate motor current
To provide feedback to the controller
Explanation - A sine‑wave inverter converts DC to a sinusoidal AC waveform suitable for AC motors.
Correct answer is: To generate a sine‑wave AC voltage for AC motors
Q.91 Which of the following statements about 'torque ripple compensation' is correct?
It increases the torque output at all times
It eliminates all torque ripple
It adds an additional control term to reduce ripple
It is not used in servo drives
Explanation - Torque ripple compensation involves adding an extra control action to counteract torque variations.
Correct answer is: It adds an additional control term to reduce ripple
Q.92 What is 'electromechanical bandwidth' in a servo drive context?
The frequency range over which the drive can maintain position accuracy
The mechanical speed limit of the motor
The electrical power supply limit
The bandwidth of the motor's back‑EMF
Explanation - Electromechanical bandwidth refers to the drive’s ability to respond to position or speed commands while maintaining accuracy.
Correct answer is: The frequency range over which the drive can maintain position accuracy
Q.93 Which of the following is a common method to improve the 'torque ripple' in a servo motor?
Using a higher resolution encoder
Increasing the supply voltage
Implementing a higher order filter
Adding a mechanical damper
Explanation - Higher order filters can smooth current ripple, thus reducing torque ripple.
Correct answer is: Implementing a higher order filter
Q.94 In servo drive design, what does the term 'gearbox backlash' refer to?
The slip between gear teeth
The difference between commanded and actual speed
The reduction ratio of the gear
The torque limit of the drive
Explanation - Backlash is the free play between meshing gears, affecting precision.
Correct answer is: The slip between gear teeth
Q.95 Which of the following is not typically part of a servo drive’s 'hardware protection' features?
Thermal shutdown
Over‑current protection
Signal filtering
Mechanical limit switches
Explanation - Signal filtering is a software or hardware filtering technique, not a protective feature per se.
Correct answer is: Signal filtering
Q.96 What is the primary purpose of a 'closed‑loop torque control' scheme?
To maintain constant speed
To match the desired torque output by adjusting current
To eliminate back‑EMF
To reduce power consumption
Explanation - Closed‑loop torque control uses current feedback to precisely regulate torque.
Correct answer is: To match the desired torque output by adjusting current
Q.97 Which of the following best describes a 'brushless DC motor' (BLDC) in servo applications?
It uses mechanical brushes for commutation
It uses electronic commutation and has no brushes
It is an AC motor
It is a stepper motor
Explanation - BLDC motors eliminate brushes, using electronic commutation for precise control.
Correct answer is: It uses electronic commutation and has no brushes
Q.98 What is a 'velocity‑mode drive' primarily used for?
Precise position hold
Maintaining a constant speed
Providing variable torque
Providing variable current
Explanation - Velocity mode focuses on speed control, not necessarily position or torque.
Correct answer is: Maintaining a constant speed
Q.99 Which of the following is an example of a 'soft‑start' technique in servo drives?
Instantly applying full current
Gradually ramping up the current command
Setting a fixed speed
Using a stepper motor
Explanation - Soft‑start reduces mechanical shock by gradually increasing current.
Correct answer is: Gradually ramping up the current command
Q.100 What is the function of a 'current sense resistor' in a servo drive?
To limit voltage
To measure the motor current for protection and feedback
To filter the encoder signal
To provide mechanical support
Explanation - The resistor creates a voltage proportional to current, used for sensing.
Correct answer is: To measure the motor current for protection and feedback
Q.101 Which of the following best defines 'torque ripple' in servo motors?
Fluctuations in speed
Fluctuations in torque during operation
Variation in voltage
Variation in current only
Explanation - Torque ripple is the periodic variation of torque output.
Correct answer is: Fluctuations in torque during operation
Q.102 What does 'dead‑time compensation' prevent in a servo drive’s gate driver?
Over‑voltage
Shoot‑through
Under‑current
Thermal runaway
Explanation - Dead‑time ensures that both high‑side and low‑side switches are off simultaneously to avoid shoot‑through.
Correct answer is: Shoot‑through
Q.103 Which of the following is a typical parameter specified by a servo drive manufacturer?
Maximum torque
Maximum speed
Maximum current
All of the above
Explanation - Manufacturers provide a full set of performance specifications.
Correct answer is: All of the above
Q.104 Which of the following is a common cause of motor heating in servo drives?
High current draw
Low supply voltage
High back‑EMF
Low switching frequency
Explanation - High current causes I²R losses, leading to heating.
Correct answer is: High current draw
Q.105 What is the main difference between a 'position servo' and a 'torque servo'?
Position servo controls position, torque servo controls torque
Position servo uses analog control, torque servo uses digital control
Position servo is slower than torque servo
Torque servo uses a higher supply voltage
Explanation - The primary control variable distinguishes the two types.
Correct answer is: Position servo controls position, torque servo controls torque
Q.106 Which type of encoder provides absolute position information in a single pulse?
Incremental encoder
Optical encoder
Absolute encoder
Hall‑sensor
Explanation - Absolute encoders give a unique position code that does not require counting from zero.
Correct answer is: Absolute encoder
Q.107 What is the typical range of switching frequencies for power MOSFETs used in servo drives?
50 Hz–100 Hz
1 kHz–10 kHz
10 kHz–100 kHz
1 MHz–10 MHz
Explanation - MOSFETs can switch up to several hundred kHz; 10‑100 kHz is common for servo applications.
Correct answer is: 10 kHz–100 kHz
Q.108 Which of these is a feature of a 'dual‑mode' servo drive?
It can operate in both position and speed modes
It can switch between AC and DC operation
It can provide two separate outputs for parallel loads
All of the above
Explanation - Dual‑mode drives can switch between control modes as needed.
Correct answer is: It can operate in both position and speed modes
Q.109 What is the purpose of a 'soft‑start' function in servo drives?
To increase starting torque
To limit the initial surge in current
To maintain constant speed
To provide continuous torque output
Explanation - Soft‑start gradually ramps the current to reduce mechanical and electrical shocks.
Correct answer is: To limit the initial surge in current
Q.110 Which of these is a key benefit of using a 'sine‑wave inverter' in servo drives?
Higher switching frequency
Reduced harmonic distortion
Lower efficiency
Simpler control algorithm
Explanation - A sine‑wave inverter produces a pure sine wave, reducing harmonics and improving motor performance.
Correct answer is: Reduced harmonic distortion
Q.111 What is the main advantage of a 'sensorless' control technique in servo drives?
Higher precision
Reduced cost by eliminating sensors
Higher current consumption
Longer response time
Explanation - Sensorless control estimates rotor position from motor signals, removing the need for physical sensors.
Correct answer is: Reduced cost by eliminating sensors
Q.112 Which of the following is a typical application of servo drives in the automotive sector?
Engine cooling fan
Transmission gear shift
Battery management system
Brake pad replacement
Explanation - Servo drives provide precise motion for gear shifting mechanisms.
Correct answer is: Transmission gear shift
Q.113 Which of the following best describes the 'current‑loop bandwidth' in a servo drive?
The rate at which the drive can change its speed
The maximum current it can supply
The frequency response of the current feedback loop
The maximum torque it can provide
Explanation - Current‑loop bandwidth refers to how quickly the loop can respond to changes in current.
Correct answer is: The frequency response of the current feedback loop
Q.114 What is 'electromechanical resonance' in a servo system?
A mismatch between motor torque and speed
A frequency at which mechanical vibrations resonate with electrical signals
The frequency at which the drive can operate
The maximum speed of the motor
Explanation - Resonance occurs when mechanical and electrical frequencies align, causing vibration amplification.
Correct answer is: A frequency at which mechanical vibrations resonate with electrical signals
Q.115 Which of the following best describes 'torque ripple compensation'?
Increasing torque output
Reducing the torque ripple by adding an additional control action
Eliminating speed variations
Decreasing motor voltage
Explanation - Torque ripple compensation uses extra control terms to smooth torque variations.
Correct answer is: Reducing the torque ripple by adding an additional control action
Q.116 What does 'closed‑loop velocity control' aim to achieve in a servo drive?
Maintain a constant torque
Maintain a constant speed
Maintain a constant position
Reduce current draw
Explanation - Velocity control focuses on keeping speed at a desired set‑point.
Correct answer is: Maintain a constant speed
Q.117 Which of these is a typical cause of motor heating in servo drives?
Low current draw
Low supply voltage
High switching losses
Low back‑EMF
Explanation - High switching frequencies or inefficient switching devices generate heat.
Correct answer is: High switching losses
Q.118 What is the main function of a 'closed‑loop torque controller' in servo drives?
To control speed
To regulate the motor current to achieve a desired torque
To maintain position
To regulate voltage
Explanation - Torque control adjusts current to match torque set‑points.
Correct answer is: To regulate the motor current to achieve a desired torque
Q.119 What is a typical purpose of the 'limit switch' in a servo system?
To monitor temperature
To provide a physical stop to prevent overtravel
To limit current
To regulate voltage
Explanation - Limit switches physically stop motion beyond safe limits.
Correct answer is: To provide a physical stop to prevent overtravel
Q.120 What does 'dead‑band' in a servo control loop refer to?
A region where the controller output is zero regardless of error
The maximum error tolerated
The time delay in the system
The bandwidth of the controller
Explanation - Dead‑band prevents controller reaction to small errors or noise.
Correct answer is: A region where the controller output is zero regardless of error
Q.121 Which of the following is a typical method used to reduce 'torque ripple' in servo motors?
Increasing the supply voltage
Adding a mechanical damper
Using a higher resolution encoder
Increasing the switching frequency
Explanation - Mechanical dampers absorb vibrations, reducing perceived torque ripple.
Correct answer is: Adding a mechanical damper
Q.122 What is the function of a 'current sense amplifier' in a servo drive?
To amplify the encoder signals
To provide high‑gain, low‑offset measurement of motor current
To convert AC to DC
To filter noise
Explanation - Current sense amplifiers provide accurate measurement for the current controller.
Correct answer is: To provide high‑gain, low‑offset measurement of motor current
Q.123 Which of the following is a characteristic of a 'sine‑wave inverter' used in servo drives?
It produces a square wave output
It produces a sine wave output
It can only drive DC motors
It is used for stepper motors
Explanation - Sine‑wave inverters generate a pure sine waveform for AC motor operation.
Correct answer is: It produces a sine wave output
Q.124 What is the main advantage of 'high‑resolution encoders' in servo applications?
Lower cost
Faster response time
Higher position accuracy
Simpler installation
Explanation - Higher resolution means more counts per revolution, enabling finer position measurement.
Correct answer is: Higher position accuracy
Q.125 Which of these is a typical safety feature in servo drives?
Over‑current protection
Thermal shutdown
Speed ramping
All of the above
Explanation - All these features protect the drive and motor from damage.
Correct answer is: All of the above
Q.126 What is 'current‑sense resistor' used for in a servo drive?
To limit voltage
To measure the motor current for protection and feedback
To filter sensor noise
To provide mechanical support
Explanation - The resistor creates a voltage proportional to current, used for sensing.
Correct answer is: To measure the motor current for protection and feedback
Q.127 Which of the following statements is true regarding 'torque ripple'?
It is caused by electrical noise only
It is the periodic variation in torque during operation
It can be ignored in high‑precision systems
It only occurs in AC motors
Explanation - Torque ripple manifests as small oscillations in torque output.
Correct answer is: It is the periodic variation in torque during operation
Q.128 What is the purpose of 'dead‑time compensation' in a gate driver?
To prevent shoot‑through
To increase switching frequency
To reduce EMI
To improve torque ripple
Explanation - Dead‑time ensures both high‑side and low‑side switches are off simultaneously.
Correct answer is: To prevent shoot‑through
Q.129 What does 'sine‑wave inverter' produce?
DC output from AC input
Sine‑wave AC voltage for AC motors
Constant current
A digital signal
Explanation - It converts DC to a sinusoidal AC waveform suitable for AC motors.
Correct answer is: Sine‑wave AC voltage for AC motors
Q.130 What is the primary benefit of using a 'sensorless' control technique?
Higher precision
Reduced cost by eliminating sensors
Lower current consumption
Longer response time
Explanation - Sensorless control estimates rotor position from motor signals, removing the need for physical sensors.
Correct answer is: Reduced cost by eliminating sensors
Q.131 Which of the following best defines 'electromechanical bandwidth'?
The frequency range over which the drive can maintain position accuracy
The mechanical speed limit of the motor
The electrical power supply limit
The bandwidth of the motor’s back‑EMF
Explanation - Electromechanical bandwidth refers to the drive’s ability to respond while maintaining accuracy.
Correct answer is: The frequency range over which the drive can maintain position accuracy
Q.132 What is 'torque ripple compensation' used for?
To increase torque output
To reduce torque ripple by adding an additional control term
To eliminate speed variations
To decrease motor voltage
Explanation - Torque ripple compensation uses extra control actions to smooth torque variations.
Correct answer is: To reduce torque ripple by adding an additional control term
Q.133 Which of these is NOT a typical feature of a servo drive’s protection system?
Over‑temperature shutdown
Over‑current protection
Thermal cut‑out
Signal filtering
Explanation - Signal filtering is a software technique rather than a protection mechanism.
Correct answer is: Signal filtering