With no output sensor in the loop, how should a timer-controlled heater be classified?
AClosed-loop control
BState feedback
CAdaptive control
DOpen-loop control
Answer: D. Open-loop control. A timer-controlled heater that does not measure its output uses open-loop control. Its action is not corrected from output feedback.
In closed-loop control, what signal is returned for comparison?
AOnly a timer
BOutput feedback
CNo reference input
DA fixed manual command
Answer: B. Output feedback. A closed-loop controller compares the reference with measured output feedback to determine its error.
The desired controlled value is also called what?
ADisturbance
BPlant output
CSetpoint
DSensor bias
Answer: C. Setpoint. The reference or setpoint specifies the desired value of the controlled output.
How is control error commonly defined?
A Feedback plus reference
B Plant input minus output
C Disturbance minus control
D Reference minus feedback
Answer: D. Reference minus feedback. For negative feedback, the error is the reference signal minus the measured feedback signal.
In control-system terminology, which element is the process being regulated?
AProcess being controlled
BOutput measuring sensor
CReference signal source
DController power supply
Answer: A. Process being controlled. The plant is the physical process or equipment whose behavior the control system regulates.
Sensors supply a measurement of which process variable for control?
AController gain only
BReference source voltage
CActuator travel limit
DSystem output or state
Answer: D. System output or state. A sensor measures a process variable and supplies a signal for control or monitoring.
How does an actuator affect the plant?
AMeasures output error
BApplies control action
CSets the reference value
DCalculates transfer poles
Answer: B. Applies control action. An actuator converts a control signal into a physical action on the plant.
The transfer function is the ratio of which quantities?
AInput over output
BOutput over input
CError over setpoint
DGain over frequency
Answer: B. Output over input. A transfer function is the Laplace-domain output-to-input ratio with zero initial conditions.
Poles of a transfer function are roots of which polynomial?
ADenominator polynomial
BNumerator polynomial
CInput polynomial
DError polynomial
Answer: A. Denominator polynomial. Poles are the roots of the transfer-function denominator after simplification.
To find transfer-function zeros, which polynomial is set to zero?
ADenominator polynomial
BNumerator polynomial
CFeedback sensor equation
DCharacteristic equation only
Answer: B. Numerator polynomial. Zeros are the values that make the transfer-function numerator equal zero.
Control systems commonly seek to achieve what outcome?
ATrack a desired response
BIncrease all disturbances
CRemove every sensor
DHold the plant open
Answer: A. Track a desired response. A controller aims to make the process output follow a desired reference and meet performance goals.
Negative feedback is used to reduce which quantity?
AAmplify the reference forever
BDisconnect the sensor
CRemove the plant model
DOutput error
Answer: D. Output error. Negative feedback compares output with the reference and drives the output error toward a smaller value.
At a summing junction, how are signed signals combined?
AStores system energy
BMeasures plant temperature
CAdds signed signals
DChanges controller type
Answer: C. Adds signed signals. A summing point algebraically combines incoming signals according to their indicated signs.
For a unit-step input, what are its initial and final values?
AOne to zero
BZero to impulse
CZero to one
DRamp to constant slope
Answer: C. Zero to one. The unit step is zero before its start time and one afterward.
Which ideal input concentrates unit area at one instant?
AConstant unit value
BLinear unit ramp
CInstantaneous unit area
DSinusoidal unit wave
Answer: C. Instantaneous unit area. The unit impulse is an idealized signal with unit area concentrated at one instant.
Unit ramps have what time-domain shape?
ALinearly increasing signal
BInstantaneous pulse
CConstant signal
DDecaying exponential only
Answer: A. Linearly increasing signal. A unit ramp increases linearly with time after it begins.
With proportional control, which quantity determines the output?
AAccumulated error only
BFuture error only
CPlant output rate only
DPresent error
Answer: D. Present error. A proportional controller produces action proportional to the current control error.
Over time, which quantity does integral action accumulate?
AOutput frequency
BPlant temperature only
CError over time
DDerivative of the reference
Answer: C. Error over time. Integral action accumulates error and can remove certain steady-state errors.
How is derivative action related to the control error?
AError rate of change
BTotal error history
CReference magnitude only
DSteady-state output only
Answer: A. Error rate of change. Derivative action responds to how quickly the error changes.
PID controllers combine which three actions?
APosition, input, delay
BPower, impedance, damping
CProportional, integral, derivative
DPlant, sensor, disturbance
Answer: C. Proportional, integral, derivative. A PID controller combines proportional, integral, and derivative actions.
Under unity feedback, how large is the feedback gain?
AZero
BInfinite
CNegative one always
DOne
Answer: D. One. Unity feedback means the feedback transfer function has a gain of one.
For negative feedback with paths G and H, which closed-loop formula applies?
AG over one plus GH
BG over one minus GH
CH over one plus G
DGH over G plus H
Answer: A. G over one plus GH. For forward path G and feedback H, negative feedback gives G/(1+GH).
Multiplying the forward and feedback paths gives which loop quantity?
AForward path times feedback
BReference divided by output
CError plus disturbance
DPlant input minus sensor
Answer: A. Forward path times feedback. Loop gain is the product of forward-path and feedback transfer functions around the loop.
Once transients settle, what does steady-state behavior describe?
AInitial condition only
BBehavior after transients settle
CThe instant of switching
DThe sensor calibration step
Answer: B. Behavior after transients settle. Steady-state behavior is the long-term response after transient effects have decayed or settled.
Which external influence can shift plant output from its target?
ADesired output command
BUnwanted external influence
CController feedback path
DTransfer-function zero
Answer: B. Unwanted external influence. A disturbance is an external influence that can alter the plant output from its desired value.