Controllers and Positioners Flashcards
The difference between the setpoint in an automatic controller and the steady-state value of the
controlled parameter is called…
A. offset.
B. gain.
C. deadband.
D. feedback.
offset
The range of values around the setpoint of a measured variable where no action occurs in an automatic
flow controller is called…
A. deviation.
B. error.
C. deadband.
D. bias.
deadband
An automatic flow controller is being used to position a valve in a cooling water system. The
controller develops a flow error signal and then increases the magnitude of the signal to drive the valve
operator.
The factor by which the magnitude of the flow error signal is increased is referred to as…
A. bias.
B. gain.
C. feedback.
D. offset.
gain
A typical flow controller uses a/an __________ method of control.
A. open-loop
B. on-off
C. closed-loop
D. external regulating
closed-loop
Which one of the following terms is used to describe the delay between a process parameter change
and the sensing of that change by the process controller?
A. Offset
B. Gain
C. Dead time
D. Time constant
Dead time
An automatic flow controller is being used to position a valve in a cooling water system. A signal
that is proportional to valve position is received by the controller. This signal is referred to as…
A. gain.
B. bias.
C. feedback.
D. error.
feedback
A flow controller has proportional, integral, and derivative control features. Which one of the
following lists the effect on the control features when the controller is switched from the automatic
mode to the manual mode?
A. Only the derivative feature will be lost.
B. Only the integral and derivative features will be lost.
C. All proportional, integral, and derivative features will be lost.
D. All control features will continue to influence the controller output.
All proportional, integral, and derivative features will be lost.
Consider a direct-acting proportional flow controller that is maintaining flow rate at a value that is
offset from the controller setpoint. If the controllers gain is increased, the controller’s offset will
__________; and the controller’s proportional band will __________.
A. decrease; decrease
B. decrease; increase
C. increase; decrease
D. increase; increase
decrease; decrease
An emergency diesel generator (DG) is operating as the only power source connected to an emergency
bus. The governor of the DG is directly sensing DG __________ and will directly adjust DG
__________ flow to maintain a relatively constant DG frequency.
A. speed; air
B. speed; fuel
C. load; air
D. load; fuel
speed; fuel
If the turbine shaft speed signal received by a typical turbine governor control system fails low during
turbine startup, the turbine governor will cause turbine speed to…
A. decrease to a minimum speed setpoint.
B. decrease until the mismatch with demanded turbine speed is nulled.
C. increase until the mismatch with demanded turbine speed is nulled.
D. increase until an upper limit is reached or the turbine trips on overspeed.
increase until an upper limit is reached or the turbine trips on overspeed.
A diesel generator (DG) is the only power source connected to an emergency bus. In this alignment,
the governor of the DG directly senses DG __________ and adjusts DG fuel flow to maintain a
relatively constant DG __________.
A. voltage; voltage
B. voltage; frequency
C. speed; voltage
D. speed; frequency
speed; frequency
If the turbine shaft speed signal received by a typical turbine governor control system fails high during
turbine startup, the turbine governor will cause turbine speed to…
A. increase until an upper limit is reached or the turbine trips on overspeed.
B. increase until the mismatch with the turbine speed demand signal is nulled.
C. decrease until a lower limit is reached or turbine steam flow is isolated.
D. decrease until the mismatch with the turbine speed demand signal is nulled.
decrease until a lower limit is reached or turbine steam flow is isolated.
Refer to the drawing of a pneumatic control system (see figure below).
An increasing steam generator (SG) water level will decrease the SG level control signal and
ultimately reduce the control air pressure applied to the feed control valve.
If the level control signal is manually increased, how will the pneumatic control system affect SG
level?
A. SG level will decrease because the valve positioner will close more, which causes the feed control
valve to close more.
B. SG level will decrease because the valve positioner will open more, which causes the feed control
valve to close more.
C. SG level will increase because the valve positioner will close more, which causes the feed control
valve to open more.
D. SG level will increase because the valve positioner will open more, which causes the feed control
valve to open more.
SG level will increase because the valve positioner will open more, which causes the feed control
valve to open more.
Refer to the drawing of a pneumatic control system (see figure below).
An increasing steam generator (SG) water level will decrease the SG level control signal and
ultimately reduce the control air pressure applied to the actuator of the feed control valve.
If the level control signal fails high, the control air pressure to the valve positioner will __________,
which will cause SG water level to __________.
A. decrease; decrease
B. decrease; increase
C. increase; decrease
D. increase; increase
increase; increase
Refer to the drawing of a water storage tank and level control system (see figure below) that have just
been returned to service following replacement of the drain valve actuator. Unfortunately, the
original direct-acting actuator was mistakenly replaced with a reverse-acting actuator.
Given:
* The drain valve will now fail open if operating air pressure is lost.
* The level control system uses a direct-acting proportional-integral level controller with a
setpoint of 15 feet.
* The level controller receives input from a direct-acting level sensor.
* The level controller is currently in manual control, with an operator maintaining the tank water
level at 14 feet.
* Tank inlet and outlet flow rates are currently equal with the drain valve 50 percent open.
If the level controller is shifted to automatic control, the tank water level will…
A. increase and stabilize at 15 feet.
B. increase and stabilize slightly higher than 15 feet.
C. decrease until the tank nearly empties.
D. increase until the tank overflows.
decrease until the tank nearly empties.
Refer to the drawing of a 30-foot water storage tank and its level control system (see figure below).
The level control system has just been returned to service following replacement of the drain valve
actuator. Unfortunately, the original direct-acting actuator was mistakenly replaced with a
reverse-acting actuator.
Given:
* The drain valve will now fail open if air pressure is lost to its actuator.
* The level control system uses a direct-acting level sensor and a direct-acting
proportional-integral level controller with a setpoint of 15 feet.
* The tank water level is stable at 16 feet with the drain valve 50 percent open.
* The level controller is in Manual control.
If the level controller is shifted to Automatic control, the tank water level will…
A. increase until the tank overflows.
B. decrease until the tank almost completely empties.
C. initially increase, and then decrease and stabilize at 15 feet.
D. initially decrease, and then increase and stabilize at 15 feet.
increase until the tank overflows.
Refer to the drawing of a water storage tank with an automatic level control system (see figure below).
The makeup valve will fail closed if its actuator loses air pressure.
Given the following possible combinations of characteristics for the level sensor and controller:
Level Sensor
Controller
- Direct-Acting Direct-Acting
- Direct-Acting Reverse-Acting
- Reverse-Acting Direct-Acting
- Reverse-Acting Reverse-Acting
Which of the above combinations will work effectively with the makeup valve in the level control
system to maintain the desired tank water level?
A. 1 only
B. 1 and 4
C. 2 only
D. 2 and 3
2 and 3
Refer to the drawing of a lube oil temperature control system (see figure below).
If the temperature transmitter fails high (high temperature output signal), the temperature controller
will position the temperature control valve more __________, causing the actual heat exchanger lube
oil outlet temperature to __________.
A. open; decrease
B. open; increase
C. closed; decrease
D. closed; increase
open; decrease
If a typical flow controller is in manual control, the output of the flow controller is determined by the…
A. operator.
B. system feedback.
C. plant computer.
D. flow error signal.
operator
Refer to the drawing of a lube oil temperature control system (see figure below).
If the temperature transmitter fails low (low temperature output signal), the temperature controller will
position the temperature control valve in the __________ direction, which causes the actual heat
exchanger lube oil outlet temperature to __________.
A. close; increase
B. close; decrease
C. open; increase
D. open; decrease
close; increase
Refer to the drawing of a lube oil temperature control system (see figure below).
Which one of the following describes the type of control used in the lube oil temperature control
system?
A. Open loop, because lube oil temperature feedback is being provided to the controller from the lube
oil temperature transmitter.
B. Open loop, because lube oil temperature is being controlled by positioning a flow control valve in
a separate system.
C. Closed loop, because lube oil temperature feedback is being provided to the controller from the
lube oil temperature transmitter.
D. Closed loop, because lube oil temperature is being controlled by positioning a flow control valve
in a separate system.
Closed loop, because lube oil temperature feedback is being provided to the controller from the
lube oil temperature transmitter.
Refer to the drawing of a lube oil temperature control system (see figure below). The temperature
control valve is currently 50 percent open.
If the cooling water inlet temperature decreases, the temperature controller will position the
temperature control valve more __________, causing cooling water differential temperature through
the heat exchanger to __________.
A. closed; increase
B. closed; decrease
C. open; increase
D. open; decrease
closed; increase
Refer to the drawing of a pressure alarm circuit (see figure below). The orientation of the bistable
symbol indicates the characteristics of the bistable, as is normal for a control circuit diagram.
The bistable turns on to actuate an alarm at a system pressure of 100 psig. The bistable has a 5 psig
deadband, or neutral zone.
If current system pressure is 90 psig, which one of the following describes the alarm circuit response
as system pressure slowly increases to 110 psig?
A. The alarm is currently actuated and will turn off at 95 psig.
B. The alarm will actuate at 100 psig and will not turn off.
C. The alarm is currently actuated and will turn off at 105 psig.
D. The alarm will actuate at 100 psig and will turn off at 105 psig.
The alarm is currently actuated and will turn off at 105 psig.
Refer to the drawing of a pressure alarm circuit (see figure below). The orientation of the bistable
symbol indicates the characteristics of the bistable, as is normal for a control circuit diagram.
The bistable turns on to actuate an alarm at a system pressure of 100 psig. The bistable has a 5 psig
deadband, or neutral zone.
If system pressure is currently 90 psig, which one of the following describes the alarm circuit response
as system pressure slowly increases to 110 psig?
A. The alarm is currently actuated and will turn off at 95 psig.
B. The alarm will actuate at 100 psig and will not turn off.
C. The alarm is currently actuated and will turn off at 105 psig.
D. The alarm will actuate at 100 psig and will turn off at 105 psig.
The alarm will actuate at 100 psig and will not turn off.