Q.1 What is the main function of a Zero-Order Hold (ZOH) in digital control?
Converts continuous-time input to discrete-time output
Samples the input signal at discrete times
Maintains the last sampled value until the next sample
Implements a derivative action on the control signal
Explanation - A ZOH holds the sampled value constant between sample instants, effectively converting a discrete control signal into a piecewise-constant analog signal.
Correct answer is: Maintains the last sampled value until the next sample
Q.2 Which discretization method uses the bilinear transform?
Euler Forward
Euler Backward
Tustin
Impulse Invariant
Explanation - The Tustin (bilinear) transform maps the s-plane to the z-plane by the substitution \(s = \frac{2}{T}(z-1)/(z+1)\).
Correct answer is: Tustin
Q.3 In a digital PID controller, what is the effect of increasing the anti-windup gain?
It increases the controller output limit
It reduces the integral windup by limiting the integrator state
It speeds up the response of the derivative term
It introduces a dead zone around zero error
Explanation - An anti-windup scheme limits the growth of the integral term when the actuator saturates, preventing excessive overshoot.
Correct answer is: It reduces the integral windup by limiting the integrator state
Q.4 Which of the following is NOT a characteristic of a first-order hold (FOH)?
It approximates a continuous ramp between samples
It results in a higher effective sampling frequency
It has a frequency response similar to a ZOH
It introduces a phase lag that is larger than a ZOH
Explanation - FOH has a smoother frequency response than ZOH and introduces less phase lag, not similar to ZOH.
Correct answer is: It has a frequency response similar to a ZOH
Q.5 What is the main advantage of using a state-space discretization over a transfer function discretization?
It always produces a higher-order discrete model
It preserves system zeros exactly
It is computationally cheaper
It is more accurate for multi-input multi-output (MIMO) systems
Explanation - State-space discretization handles MIMO systems naturally, preserving interconnections without having to derive multiple transfer functions.
Correct answer is: It is more accurate for multi-input multi-output (MIMO) systems
Q.6 In digital control, what does the term 'dead-time' refer to?
The period between sampling and quantization
The delay between a digital command and the actuator response
The time a digital signal remains constant before changing
The interval when the control loop is inactive
Explanation - Dead-time (transport delay) is the inherent delay in the system that must be accounted for in controller design to maintain stability.
Correct answer is: The delay between a digital command and the actuator response
Q.7 Which technique can be used to reduce the effect of quantization noise in a digital controller?
Increase the sampling frequency
Apply a low-pass filter to the input signal
Use a higher-order digital filter
Implement a dead-zone around zero error
Explanation - A low-pass filter smooths rapid changes, reducing the amplitude of high-frequency components where quantization noise is significant.
Correct answer is: Apply a low-pass filter to the input signal
Q.8 What is the main difference between a ZOH and a Pseudo-ZOH (PZOH)?
PZOH provides a continuous ramp between samples
PZOH is used only for analog-to-digital conversion
PZOH samples the signal twice per cycle
PZOH has no effect on the system phase
Explanation - A PZOH uses a first-order hold to approximate a continuous ramp, improving approximation accuracy over a ZOH.
Correct answer is: PZOH provides a continuous ramp between samples
Q.9 Which digital control algorithm is most suitable for controlling a servo motor with high bandwidth requirements?
PI controller
PII controller
Discrete PID with zero-order hold
Discrete PI with first-order hold
Explanation - A PID controller provides proportional, integral, and derivative actions, which are essential for high-speed servo performance.
Correct answer is: Discrete PID with zero-order hold
Q.10 How does the choice of sampling period affect the stability of a digital controller?
Shorter sampling periods always guarantee stability
Longer sampling periods always guarantee stability
Stability depends on the discrete-time poles lying inside the unit circle
Sampling period has no effect on stability
Explanation - In discrete-time systems, poles must lie inside the unit circle for stability, regardless of sampling period.
Correct answer is: Stability depends on the discrete-time poles lying inside the unit circle
Q.11 Which of the following is a typical method to design a digital controller from a continuous-time PID controller?
Tustin's method
Impulse invariance method
Zero-order hold method
All of the above
Explanation - All listed methods can be used to discretize a continuous-time PID controller, each with its own advantages.
Correct answer is: All of the above
Q.12 What role does the quantizer play in a digital control loop?
It samples the continuous-time input signal
It discretizes the continuous-time output signal
It limits the range and resolution of digital signals
It introduces anti-windup mechanisms
Explanation - Quantizers convert continuous values to a finite set of digital levels, affecting resolution and dynamic range.
Correct answer is: It limits the range and resolution of digital signals
Q.13 Which of the following best describes the 'dead-beat' controller?
A controller that drives the error to zero in one sampling period
A controller that eliminates steady-state error for a step input
A controller that uses a dead zone to avoid chattering
A controller that uses a fixed proportional gain
Explanation - Dead-beat control uses a controller design that zeros the state vector in one time step for discrete-time systems.
Correct answer is: A controller that drives the error to zero in one sampling period
Q.14 Which of the following is an advantage of using a digital controller over an analog controller?
No need for power supply
Unlimited precision
Easy to implement complex algorithms
Zero latency in processing
Explanation - Digital controllers can implement complex logic, adaptive control, and advanced filtering that are difficult in analog designs.
Correct answer is: Easy to implement complex algorithms
Q.15 What is the purpose of the 'anti-aliasing filter' before an ADC in a digital controller?
To increase the sampling frequency
To prevent high-frequency components from folding into the signal band
To provide a stable reference voltage
To quantize the input signal accurately
Explanation - An anti-aliasing filter removes frequencies above Nyquist to avoid aliasing during sampling.
Correct answer is: To prevent high-frequency components from folding into the signal band
Q.16 In a digital control loop, what is meant by 'saturation' of the actuator?
The actuator output exceeding its linear range
The actuator reaching its maximum speed
The actuator being idle
The actuator output being quantized
Explanation - Saturation occurs when the commanded signal is beyond the actuator's physical limits, causing nonlinearity.
Correct answer is: The actuator output exceeding its linear range
Q.17 Which method is used to convert a continuous-time transfer function \(G(s)\) into a discrete-time transfer function \(G(z)\) by sampling the impulse response?
Zero-order hold
Impulse invariance
Tustin
Euler backward
Explanation - Impulse invariance samples the continuous impulse response to construct the discrete transfer function.
Correct answer is: Impulse invariance
Q.18 What is the effect of a higher-order digital filter on the phase margin of a control system?
It always increases the phase margin
It always decreases the phase margin
It can increase or decrease the phase margin depending on pole-zero placement
It has no effect on the phase margin
Explanation - Higher-order filters introduce additional poles and zeros that affect phase response and therefore phase margin.
Correct answer is: It can increase or decrease the phase margin depending on pole-zero placement
Q.19 Which of the following is a common problem caused by finite word length in digital controllers?
Infinite precision
Phase lag
Overflow and wrap-around errors
Zero dead-time
Explanation - Finite word length can cause arithmetic overflow, leading to wrap-around or saturation errors.
Correct answer is: Overflow and wrap-around errors
Q.20 Which component in a digital control system is responsible for converting the continuous-time error into a discrete-time control action?
Digital-to-Analog Converter (DAC)
Analog-to-Digital Converter (ADC)
Controller core
Sample and Hold (S/H) circuit
Explanation - The controller core (e.g., digital PID) processes the discretized error signal to produce the control action.
Correct answer is: Controller core
Q.21 Which of the following describes the 'quantization error' in a digital system?
The error introduced by sampling at finite rate
The difference between the actual analog signal and the quantized digital value
The error due to dead-time delays
The error due to saturation
Explanation - Quantization error is the discrepancy between the continuous analog value and the nearest digital level.
Correct answer is: The difference between the actual analog signal and the quantized digital value
Q.22 Which of these is NOT a valid discrete-time equivalent of the continuous-time derivative operator \(s\)?
Forward difference \((z-1)/T\)
Backward difference \((z-1)/(Tz)\)
Tustin's \(\frac{2}{T}\frac{z-1}{z+1}\)
Zero-order hold \(\frac{1}{T}\ln(z)\)
Explanation - The ZOH equivalent of \(s\) is \(\frac{1}{T}\ln(z)\), but it is rarely used directly for derivative approximation.
Correct answer is: Zero-order hold \(\frac{1}{T}\ln(z)\)
Q.23 What is the main benefit of using a discrete-time state-feedback controller?
It eliminates the need for a sensor
It can directly compute control signals from state estimates
It guarantees zero steady-state error for step inputs
It is independent of system modeling
Explanation - State-feedback uses full-state information to compute control actions directly, improving performance.
Correct answer is: It can directly compute control signals from state estimates
Q.24 Which of the following is an effect of aliasing in a sampled-data system?
The sampled signal is identical to the continuous signal
High-frequency components appear as low-frequency components
All frequencies above Nyquist are attenuated
The system becomes unstable
Explanation - Aliasing maps frequencies beyond Nyquist back into the baseband, distorting the signal.
Correct answer is: High-frequency components appear as low-frequency components
Q.25 Which digital control scheme is best suited for handling actuator saturation in a robust manner?
Standard PID
PID with anti-windup
Dead-beat controller
State-feedback with saturation limiting
Explanation - Anti-windup techniques prevent the integrator from accumulating error when the actuator saturates.
Correct answer is: PID with anti-windup
Q.26 In a digital controller, what is the 'sample period' \(T\)?
Time interval between two consecutive ADC conversions
Time interval between two consecutive control updates
Time required for the controller to compute an output
Duration of the Zero-Order Hold block
Explanation - The sample period defines how often the controller reads the sensor and updates its output.
Correct answer is: Time interval between two consecutive control updates
Q.27 Which method is used to derive a digital controller directly from a continuous-time state-space model?
Euler Forward
Euler Backward
Zero-order hold discretization
All of the above
Explanation - State-space models can be discretized using Euler Forward, Euler Backward, or ZOH methods to obtain discrete equivalents.
Correct answer is: All of the above
Q.28 Why is the Tustin (bilinear) transform preferred in many digital control applications?
It maps the imaginary axis exactly onto the unit circle
It preserves the exact locations of poles and zeros
It is computationally simple
It eliminates the need for sampling
Explanation - The bilinear transform preserves stability and frequency mapping of the s-plane to the z-plane.
Correct answer is: It maps the imaginary axis exactly onto the unit circle
Q.29 What does the term 'digital integrator' refer to in the context of a digital PID controller?
A block that numerically approximates the integral of the error signal
A block that calculates the derivative of the control signal
A block that holds the last sampled value constant
A block that limits the actuator output
Explanation - The digital integrator sums error samples over time to approximate the continuous integral action.
Correct answer is: A block that numerically approximates the integral of the error signal
Q.30 Which of the following is a disadvantage of the Euler Forward discretization?
It requires a large sample period for accuracy
It introduces numerical instability for stiff systems
It cannot handle MIMO systems
It is computationally intensive
Explanation - Euler Forward can lead to instability if the sample period is not small enough, especially for stiff dynamics.
Correct answer is: It introduces numerical instability for stiff systems
Q.31 In a digital control loop, what is the purpose of a 'digital filter' applied to the sensor signal?
To increase the sampling frequency
To amplify high-frequency noise
To remove measurement noise before processing
To convert analog signals to digital
Explanation - Digital filters smooth the sensor data, improving the quality of the error signal fed to the controller.
Correct answer is: To remove measurement noise before processing
Q.32 Which of the following statements about the 'dead zone' in a digital controller is true?
It eliminates the derivative action entirely
It introduces a region around zero error where the controller output remains zero
It is used to reduce the sampling period
It is equivalent to saturation
Explanation - A dead zone prevents the controller from reacting to very small errors, avoiding unnecessary actuator activity.
Correct answer is: It introduces a region around zero error where the controller output remains zero
Q.33 What is the role of the 'control loop gain' in a digital PID controller?
It determines the sampling rate
It defines the maximum output amplitude
It sets the proportional, integral, and derivative weights
It controls the anti-aliasing filter bandwidth
Explanation - The control loop gain consists of the proportional, integral, and derivative gains that shape the controller's response.
Correct answer is: It sets the proportional, integral, and derivative weights
Q.34 In discrete-time control, what does the term 'unit step' refer to?
A step input that is applied for exactly one sample period
A step input of magnitude one applied at \(k=0\)
The response of the system to a unit impulse
The discrete-time equivalent of the continuous-time step
Explanation - A unit step in discrete time is defined as \(x[k] = 1\) for \(k \ge 0\) and zero otherwise.
Correct answer is: A step input of magnitude one applied at \(k=0\)
Q.35 Which of the following is a key consideration when designing a digital controller for a DC motor?
Choosing the right ADC resolution
Eliminating all actuator delays
Using only analog components
Avoiding any feedback in the control loop
Explanation - The ADC resolution determines the quantization noise level and impacts control accuracy.
Correct answer is: Choosing the right ADC resolution
Q.36 What is the primary function of a digital 'phase lead' compensator?
Increase the system's bandwidth
Reduce the system's steady-state error
Add phase lag to the system
Provide zero steady-state error for ramp inputs
Explanation - A phase lead compensator adds positive phase, improving stability and increasing bandwidth.
Correct answer is: Increase the system's bandwidth
Q.37 Which of the following describes the 'dead-beat' control concept?
A controller that minimizes energy consumption
A controller that reaches zero error in finite steps
A controller that uses a dead zone to avoid chatter
A controller that is robust to parameter variations
Explanation - Dead-beat control drives the error to zero in a finite number of discrete steps, typically in one sample period.
Correct answer is: A controller that reaches zero error in finite steps
Q.38 In a digital control system, what is the effect of a 'sampling delay' on stability?
It always improves stability
It has no effect on stability
It can reduce stability margins
It eliminates the need for filtering
Explanation - Sampling delay effectively adds a phase lag, reducing phase margin and potentially destabilizing the loop.
Correct answer is: It can reduce stability margins
Q.39 Which of the following best describes a 'state estimator' in digital control?
A device that measures all states directly
A digital filter that reconstructs states from measurements
A hardware block that samples the output at high frequency
A software routine that computes the derivative of the error
Explanation - A state estimator (e.g., Kalman filter) provides estimates of unmeasured states based on measured outputs.
Correct answer is: A digital filter that reconstructs states from measurements
Q.40 What is the purpose of the 'anti-windup integrator back-calculation' method?
To increase the integral gain when the actuator saturates
To adjust the integrator input to prevent windup during saturation
To eliminate the proportional term during saturation
To apply a dead zone to the error signal
Explanation - Back-calculation subtracts the difference between saturated and unsaturated outputs from the integrator input.
Correct answer is: To adjust the integrator input to prevent windup during saturation
Q.41 Which of the following statements about digital filters is correct?
They can only be implemented in hardware
They cannot reduce noise in a control system
They can be designed to have arbitrary frequency responses
They always increase the system's phase lag
Explanation - Digital filters can be designed (e.g., FIR or IIR) to meet specific magnitude and phase requirements.
Correct answer is: They can be designed to have arbitrary frequency responses
Q.42 Which of the following is an example of a 'time delay' that must be compensated in a digital control loop?
Quantization error
Sampling jitter
Propagation delay of the controller output to the actuator
Analog filter cutoff
Explanation - Propagation delay adds an additional time lag that can destabilize the loop if not compensated.
Correct answer is: Propagation delay of the controller output to the actuator
Q.43 What is the main difference between a continuous-time and a discrete-time PID controller?
Continuous-time has a derivative term while discrete-time does not
Discrete-time uses difference equations instead of differential equations
Continuous-time cannot be implemented on a microcontroller
Discrete-time cannot handle dead-time
Explanation - Digital (discrete-time) PID uses discrete difference equations to approximate continuous PID behavior.
Correct answer is: Discrete-time uses difference equations instead of differential equations
Q.44 Which of the following is NOT a type of digital filter commonly used in control systems?
FIR filter
IIR filter
Band-pass filter
Analog Butterworth filter
Explanation - Analog Butterworth filters are continuous-time; digital counterparts are designed separately.
Correct answer is: Analog Butterworth filter
Q.45 What is the main reason for using a 'state-space representation' in digital controller design?
It simplifies the derivation of transfer functions
It allows for easier discretization of multi-variable systems
It eliminates the need for a feedback loop
It reduces the sample period
Explanation - State-space models can represent MIMO systems compactly and can be discretized directly.
Correct answer is: It allows for easier discretization of multi-variable systems
Q.46 Which of the following is a consequence of a high sampling frequency in a digital controller?
Increased quantization noise
Reduced computational load
Reduced computational load due to fewer samples
Higher resolution and lower discretization error
Explanation - Higher sampling frequency captures more detail and reduces discretization errors.
Correct answer is: Higher resolution and lower discretization error
Q.47 In a digital control loop, what does the 'reference' input represent?
The desired setpoint for the controlled variable
The measurement of the controlled variable
The output of the controller
The error signal after filtering
Explanation - The reference is the target value that the controller attempts to track.
Correct answer is: The desired setpoint for the controlled variable
Q.48 What is the main function of a 'digital low-pass filter' in a control loop?
To increase the system bandwidth
To reduce high-frequency noise from sensor measurements
To amplify high-frequency disturbances
To introduce additional phase lag for stability
Explanation - A low-pass filter attenuates high-frequency components, improving measurement quality.
Correct answer is: To reduce high-frequency noise from sensor measurements
Q.49 Which of the following statements best describes 'dead-time compensation' in digital control?
It eliminates all dead-time in the system
It models the dead-time as a phase lead to cancel its effect
It uses a delay block that mirrors the actual delay
It has no impact on system stability
Explanation - Dead-time is modeled as a discrete delay block to accurately represent system behavior.
Correct answer is: It uses a delay block that mirrors the actual delay
Q.50 In digital control, what does 'sample and hold' (S/H) refer to?
An analog filter applied before the ADC
The process of storing and maintaining the sampled value
The conversion of the digital signal back to analog
The process of discretizing a continuous-time plant model
Explanation - S/H holds the analog input constant during one sampling period.
Correct answer is: The process of storing and maintaining the sampled value
Q.51 What is the primary role of a 'digital controller' in a drives system?
To directly control the mechanical load
To convert sensor readings into analog signals
To compute the control signal based on error and system model
To amplify the input signal to the actuator
Explanation - The digital controller processes the error signal and generates the actuator command.
Correct answer is: To compute the control signal based on error and system model
Q.52 Which of the following is NOT a common digital control architecture?
PDP (Processor Driven Plant)
Direct Digital Control (DDC)
Model Predictive Control (MPC)
Open-loop control
Explanation - Open-loop control lacks feedback; digital control typically requires a closed-loop architecture.
Correct answer is: Open-loop control
Q.53 Which of the following is a typical use of the 'Kalman filter' in digital control?
To perform dead-time compensation
To estimate system states from noisy measurements
To compute the derivative term of a PID controller
To reduce quantization noise directly
Explanation - Kalman filters optimally estimate states by fusing sensor data with a dynamic model.
Correct answer is: To estimate system states from noisy measurements
Q.54 What is the main benefit of using a 'state-feedback' controller over a classical PID controller?
It requires no knowledge of the plant dynamics
It can provide better performance for MIMO systems
It eliminates the need for a sensor
It is easier to tune
Explanation - State-feedback can handle multiple inputs and outputs simultaneously, improving performance.
Correct answer is: It can provide better performance for MIMO systems
Q.55 Which of the following is a common technique for reducing the effect of quantization noise in a digital control loop?
Increase the sampling frequency
Use a lower ADC resolution
Apply a high-pass filter to the control signal
Add more integrator windup
Explanation - A higher sampling rate can reduce the impact of quantization on control performance.
Correct answer is: Increase the sampling frequency
Q.56 Which digital control method uses a 'predictor-corrector' scheme?
PI controller
Model Predictive Control (MPC)
Dead-beat control
Zero-order hold control
Explanation - MPC predicts future system behavior and corrects actions accordingly.
Correct answer is: Model Predictive Control (MPC)
Q.57 In a digital controller, what does the term 'hold' refer to?
The period where the controller output is kept constant
The process of measuring the control variable
The act of storing the ADC input buffer
The period during which the controller is powered off
Explanation - The hold operation keeps the output value constant between updates.
Correct answer is: The period where the controller output is kept constant
Q.58 What is the purpose of a 'digital-to-analog converter (DAC)' in a control system?
To convert analog sensor signals into digital values
To convert the controller output to an analog signal for the actuator
To measure the controlled variable
To increase the sample rate of the digital controller
Explanation - The DAC translates the digital command into an analog voltage or current that drives the actuator.
Correct answer is: To convert the controller output to an analog signal for the actuator
Q.59 Which of the following is NOT a type of discretization error?
Quantization error
Sampling error
Round-off error
Propagation delay
Explanation - Propagation delay is a dynamic delay, not an error due to discretization.
Correct answer is: Propagation delay
Q.60 What does the 'Nyquist criterion' in digital control primarily assess?
The stability of the closed-loop system
The sampling frequency relative to the signal bandwidth
The resolution of the ADC
The presence of quantization noise
Explanation - The Nyquist criterion uses the frequency response to determine system stability.
Correct answer is: The stability of the closed-loop system
Q.61 Which of the following describes the 'integrator windup' phenomenon?
The integrator term decays too fast
The integrator accumulates error during actuator saturation
The integrator introduces phase lag at high frequencies
The integrator is disabled during steady-state
Explanation - During saturation, the integrator may continue to accumulate error, leading to windup.
Correct answer is: The integrator accumulates error during actuator saturation
Q.62 What is the main difference between a 'Zero-Order Hold (ZOH)' and a 'First-Order Hold (FOH)'?
ZOH holds the value constant, FOH holds a linear ramp
ZOH samples at a higher rate than FOH
ZOH is used only in analog control, FOH in digital control
ZOH has no effect on phase lag, FOH does
Explanation - FOH approximates the input with a ramp, improving accuracy over a ZOH.
Correct answer is: ZOH holds the value constant, FOH holds a linear ramp
Q.63 Which of the following is a typical benefit of using a 'digital controller' in an industrial drive?
It eliminates the need for a power supply
It allows for easy implementation of advanced control strategies
It guarantees zero steady-state error for all inputs
It removes the requirement for an ADC
Explanation - Digital controllers can run complex algorithms, such as MPC or adaptive control.
Correct answer is: It allows for easy implementation of advanced control strategies
Q.64 Which of the following is the main role of the 'sample time' in a digital controller?
To determine the number of inputs the controller can handle
To set the resolution of the DAC
To decide how often the control law is updated
To specify the maximum control output
Explanation - The sample time controls the frequency at which the controller updates its output.
Correct answer is: To decide how often the control law is updated
Q.65 Which technique is used to mitigate the effect of quantization noise in a digital control loop?
Use of higher-order filters
Use of a larger sample period
Use of a smaller ADC resolution
Use of a dead zone
Explanation - Higher-order filters can better attenuate high-frequency quantization noise.
Correct answer is: Use of higher-order filters
Q.66 In digital control, what does the 'digital controller gain' refer to?
The number of bits in the ADC
The proportional, integral, and derivative gains
The sampling frequency
The maximum output of the DAC
Explanation - The digital controller gain comprises the PI or PID coefficients used in the controller algorithm.
Correct answer is: The proportional, integral, and derivative gains
Q.67 Which of the following is a common digital control strategy used for motor drives?
Open-loop position control
Fuzzy logic control
Proportional control only
Analog PID control
Explanation - Fuzzy logic controllers are frequently used in motor drives to handle nonlinearities.
Correct answer is: Fuzzy logic control
Q.68 What is the main disadvantage of increasing the sampling frequency in a digital control system?
It reduces the system bandwidth
It increases the quantization noise level
It increases computational load and power consumption
It reduces the resolution of the ADC
Explanation - Higher sample rates require more processing cycles, which can increase power usage.
Correct answer is: It increases computational load and power consumption
Q.69 Which of the following is a key consideration when designing a digital filter for control?
The filter must be a Butterworth filter
The filter must have an infinite impulse response
The filter must not introduce phase lag that destabilizes the loop
The filter must be implemented in hardware only
Explanation - Phase lag can reduce stability margins; filter design must account for this.
Correct answer is: The filter must not introduce phase lag that destabilizes the loop
Q.70 What is the purpose of the 'deadband' in a digital controller?
To increase the controller's sampling period
To prevent small oscillations around zero error
To compensate for dead-time in the actuator
To limit the maximum output voltage
Explanation - A deadband stops the controller from reacting to very small errors, reducing chatter.
Correct answer is: To prevent small oscillations around zero error
Q.71 Which of the following best describes a 'digital state-space controller'?
A controller that uses only analog signals
A controller that computes state feedback in discrete time
A controller that operates in continuous time only
A controller that uses PID tuning rules
Explanation - A digital state-space controller applies a state-feedback law derived from discrete state equations.
Correct answer is: A controller that computes state feedback in discrete time
Q.72 What is the effect of a 'digital delay' block in a control loop?
It adds a fixed time lag between input and output
It increases the system's bandwidth
It eliminates the need for an ADC
It reduces the control loop's sampling frequency
Explanation - A digital delay introduces a specified number of sample delays, modeling dead-time.
Correct answer is: It adds a fixed time lag between input and output
Q.73 Which of the following best describes a 'digital PI' controller?
A controller that uses proportional and integral actions in discrete time
A controller that only uses the integral action
A controller that uses proportional, integral, and derivative actions
A controller that uses a dead zone only
Explanation - Digital PI includes P and I terms calculated in discrete time.
Correct answer is: A controller that uses proportional and integral actions in discrete time
Q.74 Which of the following is an advantage of using a 'digital controller' in a safety-critical system?
It can be programmed to implement fail-safe logic
It requires no testing
It has infinite precision
It does not need to interface with sensors
Explanation - Digital controllers can run safety routines and switch to safe modes when faults are detected.
Correct answer is: It can be programmed to implement fail-safe logic
Q.75 Which of the following is an example of a 'sampling error'?
Error due to quantization of the analog signal
Error introduced by a finite word length
Error due to the discrete representation of a continuous signal
Error due to a misconfigured DAC
Explanation - Sampling error arises because the continuous signal is represented by discrete samples.
Correct answer is: Error due to the discrete representation of a continuous signal
Q.76 In a digital control system, what is a 'look-up table (LUT) controller'?
A controller that stores sensor values in memory
A controller that approximates a nonlinear function via precomputed values
A controller that uses a lookup of PID parameters
A controller that directly measures the system state
Explanation - A LUT uses stored values to approximate complex relationships without real-time computation.
Correct answer is: A controller that approximates a nonlinear function via precomputed values
Q.77 Which of the following statements about 'digital notch filter' is correct?
It amplifies a narrow frequency band
It removes a narrow frequency band from the signal
It has no effect on the phase response
It is only used in analog systems
Explanation - A digital notch filter attenuates a specific frequency, useful for eliminating resonances.
Correct answer is: It removes a narrow frequency band from the signal
Q.78 What is the purpose of the 'error signal' in a digital control loop?
To represent the difference between reference and measurement
To represent the actuator output
To store the previous control signal
To act as a low-pass filter
Explanation - The error signal drives the controller; it is the basis for control actions.
Correct answer is: To represent the difference between reference and measurement
Q.79 Which of the following is an advantage of using a 'digital IIR filter' over an FIR filter?
Higher computational cost
Fewer coefficients needed for a given performance
Unlimited filter order
No phase distortion
Explanation - IIR filters achieve similar performance with fewer coefficients, reducing computational load.
Correct answer is: Fewer coefficients needed for a given performance
Q.80 In digital control, which of the following is a 'deadband' effect?
The controller output increases linearly with error
The controller output is zero within a small error range
The controller output saturates immediately
The controller output is always maximum
Explanation - A deadband sets the controller output to zero for errors below a threshold.
Correct answer is: The controller output is zero within a small error range
Q.81 Which of the following best describes 'digital PID tuning'?
Adjusting the parameters to meet performance criteria in continuous time
Adjusting the parameters to meet performance criteria in discrete time
Using only analog methods to tune the controller
Setting the parameters to zero
Explanation - Digital PID tuning considers the sample period and discretization effects.
Correct answer is: Adjusting the parameters to meet performance criteria in discrete time
Q.82 Which of the following is NOT a common source of nonlinearity in digital control loops?
Actuator saturation
Quantization noise
Sampling jitter
Ideal ADC
Explanation - An ideal ADC introduces no nonlinearity; real ADCs can introduce quantization and nonlinearities.
Correct answer is: Ideal ADC
Q.83 What does the 'sample period' \(T\) represent in the context of discretization of a continuous-time system?
The time step at which the system is sampled
The period of the system's natural oscillation
The time delay introduced by the DAC
The duration of the zero-order hold
Explanation - The sample period is the interval between successive samples in the discrete model.
Correct answer is: The time step at which the system is sampled
Q.84 In a digital control system, what does the term 'quantization' refer to?
The process of converting a digital signal to analog
The process of converting an analog signal to a finite set of digital levels
The process of reducing the sample rate
The process of applying a low-pass filter
Explanation - Quantization maps a continuous range to discrete levels, creating quantization error.
Correct answer is: The process of converting an analog signal to a finite set of digital levels
Q.85 Which of the following best describes a 'dead-beat controller' in discrete-time systems?
A controller that introduces dead-time to the system
A controller that eliminates the derivative action
A controller that drives the error to zero in a finite number of steps
A controller that uses only a proportional gain
Explanation - Dead-beat control uses state feedback to cancel the state in a finite number of samples.
Correct answer is: A controller that drives the error to zero in a finite number of steps
Q.86 What is the main function of a 'digital filter' in a sensor measurement path?
To increase the sensor's output range
To reduce measurement noise before it enters the controller
To convert digital data back to analog
To delay the sensor signal by several samples
Explanation - Filtering cleans up the sensor data, improving the controller's accuracy.
Correct answer is: To reduce measurement noise before it enters the controller
Q.87 Which of the following is a benefit of using a 'digital PI' controller compared to a 'digital PID' controller?
It can handle dead-time better
It has simpler implementation when the derivative term is noisy
It guarantees zero steady-state error for ramp inputs
It requires a higher sampling rate
Explanation - Dropping the derivative term avoids amplification of high-frequency noise.
Correct answer is: It has simpler implementation when the derivative term is noisy
Q.88 What does the term 'digital hold' refer to in a digital control loop?
The process of holding a digital value constant for a duration
The act of converting analog to digital
The process of quantization
The delay introduced by the ADC
Explanation - In discrete control, the controller output is held constant between updates.
Correct answer is: The process of holding a digital value constant for a duration
Q.89 Which of the following is a common cause of 'integrator windup' in digital controllers?
Using a very small sampling period
Using a very large proportional gain
Actuator saturation preventing the integrator from outputting its value
Applying a low-pass filter to the error signal
Explanation - When the actuator saturates, the integrator continues to integrate, causing windup.
Correct answer is: Actuator saturation preventing the integrator from outputting its value
Q.90 In digital control, which of the following is a primary reason to use a 'dead zone' around the error signal?
To increase the system bandwidth
To prevent small oscillations caused by measurement noise
To eliminate the need for a DAC
To reduce the sampling period
Explanation - A dead zone reduces sensitivity to noise, preventing unnecessary control actions.
Correct answer is: To prevent small oscillations caused by measurement noise
Q.91 Which of the following describes the 'discrete-time integrator' in a PID controller?
A block that calculates the derivative of the error
A block that accumulates the error over time using a summation
A block that holds the last error value constant
A block that implements the proportional term only
Explanation - The discrete integrator sums error samples weighted by the sample period.
Correct answer is: A block that accumulates the error over time using a summation
Q.92 In digital control, what is a 'sample-and-hold' device primarily used for?
To sample the sensor at a high frequency
To convert a digital signal to analog
To maintain a constant analog value between sample instants
To filter out high-frequency noise
Explanation - The sample-and-hold holds the sampled value constant until the next sampling instant.
Correct answer is: To maintain a constant analog value between sample instants
Q.93 Which of the following is a typical design goal for a digital controller in an industrial drive?
Maximum possible actuator saturation
Zero steady-state error for a step input
Maximum possible phase lag
Minimum number of states in the model
Explanation - Zero steady-state error ensures accurate position or speed tracking.
Correct answer is: Zero steady-state error for a step input
Q.94 Which of the following best explains 'anti-aliasing' in a digital control system?
Removing low-frequency components before sampling
Removing high-frequency components before sampling
Increasing the sampling rate to avoid aliasing
Quantizing the signal more finely
Explanation - An anti-aliasing filter attenuates frequencies above Nyquist to prevent aliasing.
Correct answer is: Removing high-frequency components before sampling
Q.95 Which of the following statements about 'digital filter delay' is correct?
It is always zero
It introduces a phase shift that is proportional to frequency
It only occurs in analog filters
It is independent of the filter order
Explanation - Digital filters inherently introduce a delay that increases with frequency and filter order.
Correct answer is: It introduces a phase shift that is proportional to frequency
Q.96 Which of the following is a typical effect of increasing the integral gain in a digital PID controller?
Reduced steady-state error
Increased settling time
Decreased overshoot
Higher computational complexity
Explanation - A higher integral gain drives steady-state error to zero more quickly, but may increase overshoot.
Correct answer is: Reduced steady-state error
Q.97 Which of the following is NOT a characteristic of a 'dead-beat' controller?
Finite-time error elimination
Requires knowledge of the full state vector
Uses a high sampling frequency
Can be designed for both SISO and MIMO systems
Explanation - Dead-beat control can be implemented at any sample rate; the key is state feedback.
Correct answer is: Uses a high sampling frequency
Q.98 Which of the following best describes the 'quantization noise' in digital control?
Random error caused by thermal noise in the ADC
Deterministic error caused by converting to a finite number of levels
Error due to delayed sampling
Error due to high-pass filtering
Explanation - Quantization noise arises from rounding the continuous signal to discrete levels.
Correct answer is: Deterministic error caused by converting to a finite number of levels
Q.99 What is the primary purpose of the 'dead-time compensator' in a digital control loop?
To remove all dead-time in the system
To model the dead-time accurately for controller design
To increase the system bandwidth
To eliminate quantization noise
Explanation - Dead-time is modeled as a discrete delay to be considered in the controller design.
Correct answer is: To model the dead-time accurately for controller design
Q.100 Which of the following is a benefit of using a 'digital notch filter' in a control system?
It increases the system bandwidth
It eliminates a specific frequency component causing resonances
It introduces a large phase lag
It is only used for digital signal processing, not control
Explanation - Notch filters suppress unwanted resonant frequencies, improving control stability.
Correct answer is: It eliminates a specific frequency component causing resonances
Q.101 In a digital control system, which of the following best describes the 'sampling theorem'?
It states that the sample period must be shorter than the system's settling time
It states that the sampling rate must be at least twice the highest frequency component in the signal
It states that the ADC resolution must be higher than the DAC resolution
It states that the digital filter must have a Butterworth response
Explanation - The sampling theorem (Nyquist) ensures that a signal can be perfectly reconstructed.
Correct answer is: It states that the sampling rate must be at least twice the highest frequency component in the signal
Q.102 Which of the following is an advantage of using a 'digital PI' controller over a 'digital PID' controller?
It can achieve zero steady-state error for ramp inputs
It has a simpler implementation when high-frequency noise is present
It can handle larger actuator saturations
It always requires a higher sampling rate
Explanation - Dropping the derivative term reduces sensitivity to measurement noise.
Correct answer is: It has a simpler implementation when high-frequency noise is present
Q.103 Which of the following statements about the 'digital controller' is true?
It cannot be used with analog sensors
It must be implemented in hardware only
It can run advanced algorithms like MPC
It does not require a power supply
Explanation - Digital controllers can implement complex control strategies due to computational flexibility.
Correct answer is: It can run advanced algorithms like MPC
Q.104 Which of the following best describes a 'digital low-pass filter' applied to a control error signal?
It amplifies high-frequency components of the error
It attenuates high-frequency components of the error
It eliminates the error completely
It has no effect on the error
Explanation - A low-pass filter removes high-frequency noise from the error before control action.
Correct answer is: It attenuates high-frequency components of the error
Q.105 What does the term 'state-space representation' mean in the context of digital control?
A representation that uses transfer functions only
A representation that describes the system in terms of state variables
A representation that uses only input-output data
A representation that only applies to continuous-time systems
Explanation - State-space uses state equations to model system dynamics, suitable for multi-variable control.
Correct answer is: A representation that describes the system in terms of state variables
Q.106 Which of the following is a key reason to use a 'digital filter' in a control loop?
To increase the sampling rate
To reduce measurement noise and improve control performance
To eliminate the need for an ADC
To increase the controller's output range
Explanation - Filtering improves signal quality, enhancing controller accuracy.
Correct answer is: To reduce measurement noise and improve control performance
Q.107 What is a 'deadband' in the context of a digital controller?
A time interval where the controller is inactive
A range of error values for which the controller output is zero
A region of high-frequency noise
A fixed delay introduced by the ADC
Explanation - Deadband prevents small errors from triggering actuator changes, reducing chatter.
Correct answer is: A range of error values for which the controller output is zero
Q.108 In digital control, which of the following best describes the 'discrete-time integrator'?
A block that computes the derivative of the error
A block that sums the error samples over time
A block that holds the last error value constant
A block that implements the proportional action only
Explanation - The integrator accumulates error samples to approximate the continuous integral.
Correct answer is: A block that sums the error samples over time
Q.109 Which of the following is a major advantage of using a digital controller in a motor drive?
It eliminates the need for a power supply
It allows for precise tuning of controller parameters
It guarantees zero steady-state error for all inputs
It removes actuator saturation completely
Explanation - Digital controllers enable fine parameter adjustments via software without hardware changes.
Correct answer is: It allows for precise tuning of controller parameters
Q.110 Which of the following best describes an 'IIR' digital filter?
It uses only a finite number of taps
It has an infinite impulse response due to feedback
It can only be implemented in hardware
It has a zero frequency response
Explanation - IIR filters incorporate feedback, resulting in an impulse response that theoretically never ends.
Correct answer is: It has an infinite impulse response due to feedback
Q.111 In digital control, what is the primary reason to use a 'dead-time compensator'?
To reduce the sampling period
To model the effect of transport delay accurately in controller design
To increase the system's bandwidth
To eliminate the need for a DAC
Explanation - Dead-time compensators ensure that controller design accounts for actual system delays.
Correct answer is: To model the effect of transport delay accurately in controller design