Chapter 8 Flashcards
in feedback control, when the measured value s equal to the setpoint:
a. the error is zero
b. a disturbance is introduced
c. the process stops
d. the controller output is maximum
a. the error is zero
which component in a feedback control loop directly measures the controlled variable?
a. controller
b. valve
c. actuator
d. sensor
d. sensor
combine feedforward and feedback control helps to:
a. eliminate the sensor entirely
b. simplify the loop structure
c. remove the need for a controller
d. address both measurable and unmeasurable disturbances
d. address both measurable and unmeasurable disturbances
in a block diagram, a controller processes the:
a. output of the process
b. error between setpoint and measured variable
c. input from the disturbance
d. actuator signal
b. error between setpoint and measured variable
a feedback control loop requires which of the following components?
a. disturbance model, predictor
b. operator, control chart
c. setpoint, controller, pump
d. actuator, controller, sensor
d. actuator, controller, sensor
a controller compares the setpoint and process variable to produce:
a. a disturbance output
b. a sensor signal
c. the error signal
d. a steady-state value
c. the error signal
in a block diagram, the disturbance is typically introduced:
a. into the process block
b. after the sensor
c. in parallel with the actuator
d. before the controller
a. into the process block
which of the following best describes closed-loop control?
a. input changes are ignored
b. output is fed back and compared with the input
c. process gain is set to unity
d. control action is independent of output
b. output is fed back and compared with the input
a disturbance entering after the final control element can:
a. be ignored as it affects only input
b. be compensated using feedforward control
c. be perfectly corrected by feedback
d. not be corrected by feedback control
c. be perfectly corrected by feedback
the final control element (FCE) is typically:
a. a controller
b. a disturbance generator
c. a sensor
d. a valve or motor
d. a valve or motor
In feedback control, the objective is to
reduce the error signal to zero
An inherent disadvantage of proportional-only control is that
a steady-state error occurs after a set-point change or a sustained disturbance.
For proportional controllers, bias can be adjusted, a procedure referred to
as manual reset
For integral control action, the controller output depends on
the integral of the error signal over time
an adjustable parameter referred to as __________, has units of time.
the integral time or reset time
Integral control action is widely used because it provides an important practical advantage, _______
the elimination of offset
integral control action is normally used in conjunction with proportional control as
the proportional-integral (PI) controller
An inherent disadvantage of integral control action is a phenomenon known as
reset windup or integral windup
When a sustained error occurs, the integral term becomes
quite large and the controller output eventually saturates.
Further buildup of the integral term while the controller is saturated is referred to as
reset windup or integral windup.
The function of derivative control action is
to anticipate the future behavior of the error signal by considering its rate of change.
the derivative term includes a ___________ that reduces the sensitivity of the control calculations to high-frequency noise in the measurement.
derivative mode filter (also called a derivative filter)
three most common forms of PID controllers
parallel (without derivative filter), series (with derivative filter), expanded
is a tuning parameter and largely determines the controller aggressiveness.
the controller gain
is a tuning parameter and determines the amount of integral action
the reset time
is a tuning parameter and determines the amount of derivative action.
the derivative time
One disadvantage of the previous PID controllers is that
a sudden change in set point (and hence the error, e) will cause the derivative term momentarily to become very large and thus provide a derivative kick to the final control element.
This controller is an example of a reverse-acting controller.
when Kc > 0
the controller is said to be direct acting because the controller output increases as the input increases.
When Kc < 0
Manual Mode is very useful when unusual
conditions exist:
plant start-up
plant shut-down
emergencies
On-Off Controllers synonym
“two-position” or “bang-bang” controllers.
There are two alternative forms of the digital PID control equation,
the position form and the velocity form
referred to as _______ of the PID control algorithm because the actual value of the controller output is calculated
the position form
In the _____, the change in controller output is calculated
velocity form
The velocity form has three advantages over the position form:
- It inherently contains anti-reset windup
- that can be utilized directly by some final control elements, such as a control valve driven by a pulsed stepping motor.
- transferring the controller from manual to automatic mode does not require any initialization of the output
