Modules 4 & 5 Flashcards

1
Q

Components in a feedback loop usually have some form of signal communication
because:
a. The controller may be a stand-alone device in a digital system.
b. Wireless communication cannot replace electrical signal transmission.
c. The components may be physically separated.
d. A backup to a manual system must employ shared digital signals.

A

c. The components may be physically separated.

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2
Q

Which of the following statements is TRUE regarding controller tuning from
closed loop tests?
a. The magnitude of the oscillation required can be easily predicted.
b. Moderate disturbances during the testing can be tolerated.
c. Multiple tests are usually not required, minimizing interruption to normal
operations.
d. The technique is based on the assumption that a first order plus dead time
(FOPDT) process model approximates the real process.

A

b. Moderate disturbances during the testing can be tolerated.

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3
Q

Which of the following are valid forms of PID algorithm?
a. Proportional and derivative modes on error, integral on measurement
b. Proportional and integral modes on measurement, derivative on error
c. Proportional, integral, and derivative modes on measurement
d. Proportional, integral, and derivative modes on error

A

d. Proportional, integral, and derivative modes on error

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4
Q

Which of the following valve actuators has the lowest cost and low friction and
deadband?
a. Electric
b. Solenoid
c. Pneumatic
d. Hydraulic

A

c. Pneumatic

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5
Q

Which of the following would be able to indicate both direction and velocity?
a. +/– 10 V
b. 4 – 20 mA
c. 10 – 50 mA
d. 3 – 15 psi

A

a. +/– 10 V

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6
Q

Which control measurement is generally expressed as the ratio of the error to the
full-scale output?
a. Response
b. Accuracy
c. Linearity
d. Repeatability

A

b. Accuracy

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7
Q

A piping and instrument diagram does NOT include which of the following?
a. Communication between instrumentation devices
b. Accessibility of devices to the operator
c. Failure thresholds
d. Instrumentation devices

A

c. Failure thresholds

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8
Q

Which of the following is TRUE of the relay method of tuning?
a. The relay method is not appropriate for automated testing.
b. The process is tested by a forced disturbance using an on-off controller.
c. The controlled variable will stay at the setpoint, with the controller output at the
minimum value.

A

b. The process is tested by a forced disturbance using an on-off controller.

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9
Q

The purpose of the plug within the control valve is to
a. send a signal to the control valve to maintain the setpoint.
b. create a flow area that modifies the flow rate.
c. measure the upstream pressure of the property.
d. allow the valve to rotate without any linear motion.

A

b. create a flow area that modifies the flow rate.

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10
Q

A pneumatic positioner is used to
a. increase fast venting capability.
b. overcome packing friction.
c. eliminate use of piston actuators.
d. diagnose itself and the valve actuator system.

A

b. overcome packing friction.

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11
Q

Which of the following is true of electric signaling?
a. The ISA SP50 committee developed a 3 mA to 15 mA signal standard.
b. The ISA SP50 committee used a three-wire loop consisting of one ground, one
current, and one signal wire.
c. Electric signaling still required an external air supply to actuate the final control
element.
d. Electric signaling overcame the dead time drawback of pneumatic signaling.

A

d. Electric signaling overcame the dead time drawback of pneumatic signaling.

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12
Q

Which of the following is characteristic of controlled processes?
a. Process measurements usually provide positive feedback.
b. Processes will exhibit zero error.
c. Controlled processes with identical equipment will respond identically.
d. A change in one controller may affect a number of process variables.

A

d. A change in one controller may affect a number of process variables.

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13
Q

Trial-and-error tuning is BEST accomplished by
a. minimizing the effects of the decay ratio.
b. using an open loop test to define tuning parameters.
c. adjusting the relationship between the integral time and the period of
oscillation.
d. examining the as-found data set related to the process.

A

c. adjusting the relationship between the integral time and the period of
oscillation.

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14
Q

What is the difference between a linear valve and a rotary valve?
a. A linear valve is suited to low pressure applications; a rotary valve can handle
high pressure applications.
b. A linear valve has a low recovery; a rotary valve has a high recovery.
c. A linear valve has an integral bonnet; a rotary valve has a separable bonnet.
d. A linear valve is flangeless; a rotary valve is usually threaded.

A

b. A linear valve has a low recovery; a rotary valve has a high recovery.

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15
Q

When using a two-wire electric signal loop to carry both the current and the signal,
which of the following is true?
a. Ohm’s Law states that as voltage is raised across a device, the current is
proportionally increased and the change in current is used as the signal.
b. A solid state device such as a bipolar triode transistor is required to keep
variance in voltage from affecting current (within reason).
c. A solid state device such as a bipolar triode transistor will determine the
collector current and not the emitter-base current (within reason).
d. Ohm’s Law states that as voltage is raised across a device, the current
remains constant and current can therefore be used to carry the signal.

A

b. A solid state device such as a bipolar triode transistor is required to keep
variance in voltage from affecting current (within reason).

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16
Q

In the ideal PID algorithm, the derivative mode may be used to
a. control the feedback device.
b. control the reset rate.
c. provide most of the correction.
d. improve response of the control loop.

A

d. improve response of the control loop.

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17
Q

The simplest technique for addressing the nonlinearity problem is
a. trial-and-error tuning.
b. scheduled tuning.
c. closed loop tuning.
d. self-tuning.

A

b. scheduled tuning.

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18
Q

What is the MOST important thing to know in troubleshooting a valve problem?
a. Temperatures the valve is exposed to
b. Fail-safe mode of the valve
c. Velocity of the valve
d. Composition of the valve

A

b. Fail-safe mode of the valve

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19
Q

Which of the following is true of analog versus digital communications?
a. Analog signals are obsolete and are being entirely replaced by digital signals.
b. The lowest level of communications in the control hierarchy is still
predominantly analog.
c. The telephone and telegraph are early examples of analog communications.
d. Analog signals model a physical quantity using a number of discrete states
between an upper and lower range limit.

A

b. The lowest level of communications in the control hierarchy is still
predominantly analog.

20
Q

A two-wire loop with a loop power supply of 26 V has a 200 ohm load resistor and
50 ohms loop resistance. If the maximum current in the loop should be 20 mA, what
is the voltage drop and how much voltage will be across the transmitter at 20 mA?
a. 4 V drop and 22 V across the transmitter at 20 mA
b. 4 V drop and 26 V across the transmitter at 20 mA
c. 5 V drop and 21 V across the transmitter at 20 mA
d. 6 V drop and 20 V across the transmitter at 20 mA

A

c. 5 V drop and 21 V across the transmitter at 20 mA

21
Q

Bumpless transfer is an issue in which of the following?
a. Time-proportioning control
b. Manual-automatic switching
c. Direct and reverse acting
d. Interactive PID algorithm

A

b. Manual-automatic switching

22
Q

Which of the following statements about process disturbances is true?
a. Reducing the variability of disturbances can be done by the feedback
controller.
b. Feedback controllers will maintain the average value of the controlled variable
at setpoint if disturbances are not severe.
c. Severe disturbances will create minimal feedback in the control loop because
the controller minimizes output changes.
d. Reducing the margin of safety will increase the number of process
disturbances.

A

b. Feedback controllers will maintain the average value of the controlled variable
at setpoint if disturbances are not severe.

23
Q

Which of the following is a rotary valve?
a. Diagram
b. Gate
c. Butterfly
d. Globe

A

c. Butterfly

24
Q

In a Watts governor for a steam engine, which of the following represents the upper
range value of the system?
a. Gain adjustment position for the least change in the output signal
b. Bridle position for the highest speed permitted
c. Bridle position for the lowest speed permitted
d. Gain adjustment position for the most change in the output signal

A

b. Bridle position for the highest speed permitted

25
Q

A constant current transmitter with a 24 V power supply drops 1.2 V at minimum
current at a resistance of 300 ohms. Which of the following correctly identifies how
the output current is determined?
a. The transmitter will have 22.8 V resulting in 7.6 mA current.
b. The output current is decided by process variable and calibration.
c. The transmitter will have 24 V resulting in a 4 mA current.
d. The output current is decided by voltage on the transmitter per Ohm’s Law.

A

b. The output current is decided by process variable and calibration.

26
Q

In a direct acting controller, an increase in the controlled variable will cause the
output to
a. decrease.
b. increase.
c. fail.
d. do nothing.

A

b. increase.

27
Q

In cascade control, the primary loop controller
a. must be significantly faster than the secondary loop controller.
b. establishes the setpoint for the secondary loop controller.
c. eliminates the need for a feedback control loop.
d. corrects and confines disturbances in the secondary loop controller

A

b. establishes the setpoint for the secondary loop controller.

28
Q

In a post-guided valve application, the valve
a. is well suited for slurries and fluids with entrained solids.
b. uses a shaft to connect the closure member to the actuator.
c. is positioned in the active flow stream.
d. has a cylindrical plug with a seat ring.

A

a. is well suited for slurries and fluids with entrained solids.

29
Q

In a Watts governor for a steam engine, which of the following allows an operator to
change the span between upper and lower range values?
a. Flyweight
b. Gain
c. Bridle
d. Shaft speed

A

b. Gain

30
Q

What is the span of a 4 to 20 mA signal, and what is its live zero?
a. 20 mA span and 0 mA live zero
b. 16 mA span and 0 mA live zero
c. 16 mA span and 4 mA live zero
d. 20 mA span and 4 mA live zero

A

c. 16 mA span and 4 mA live zero

31
Q

A configuration option that permits the user to make the derivative mode sensitive
only to changes in the controlled variable, not to the setpoint, is called
a. proportional band variable.
b. derivative-on-measurement.
c. proportional controller offset.
d. reset action.

A

b. derivative-on-measurement.

32
Q

Which of the following statements is NOT true of feedforward control?
a. Feedforward control is used in a similar fashion to integral control.
b. Feedforward control synchronizes the effects of a disturbance and the control
action.
c. Feedforward control modifies the output of the feedback controller when
feedback and feedforward control are used together.
d. Feedforward control is intended to compensate for external disturbances to a
control loop.

A

a. Feedforward control is used in a similar fashion to integral control.

33
Q

In selecting the appropriate control valve, the INITIAL consideration is
a. determining the pressure rating of the valve.
b. calculating the valve sizing coefficient.
c. determining the degree of pressure recovery downstream.
d. identifying the point of highest fluid velocity and lowest pressure.

A

b. calculating the valve sizing coefficient.

34
Q

Which of the following is true of signals prior to when standard signals were
common?
a. Measuring flow by differential pressure involved running a thermocouple
extension wire to the control room.
b. The signal to the final control element for thermocouples was some form of
pneumatic or mechanical transmission.
c. Measuring flow by differential pressure involved a pneumatic relay in which an
electric gate opened and closed a remote airflow.
d. RTDs developed two-wire applications to overcome the limitations of long
leads.

A

b. The signal to the final control element for thermocouples was some form of
pneumatic or mechanical transmission.

35
Q

In a 4 to 20 mA signal that corresponds to a 0 to 100% scale, what would the
current be at 50%?
a. 4 mA
b. 8 mA
c. 12 mA
d. 16 mA

A

c. 12 mA

36
Q

Digital processing of the PID algorithm presents which of the following alternatives
not available in an analog system?
a. Correction of integral windup, eliminating overshoots in the controlled
response
b. Setting of the control to any reasonable arbitrary level
c. Reduction of the error between setpoint and output
d. Calculation of the increment by which the controller output should be changed

A

d. Calculation of the increment by which the controller output should be changed

37
Q

Which of the following statements about forward decoupling is NOT true?
a. It allows setpoint changes to affect only the desired controlled variables.
b. It uses a configuration where each process input is a combination of a
controller output and the other process input.
c. It is used to reduce control loop interactions.
d. It is closely related to feedforward control.

A

b. It uses a configuration where each process input is a combination of a
controller output and the other process input.

38
Q

Which type of control valve is MOST appropriate for handling a low pressure drop in
a pipe over two inches in diameter?
a. Linear motion globe/angle type with cage
b. Butterfly
c. Ball
d. Linear motion globe/angle type with simple plug

A

b. Butterfly

39
Q

Which of the following statements about controller tuning is accurate for most
applications?
a. Controller tuning techniques require a formal testing of the process.
b. A response to setpoint change that provides a quarter-amplitude decay
reaction curve is preferred.
c. The penalty for aggressive tuning is that a disturbance will require a greater
time to return to setpoint.
d. The controller tuner must decide the acceptable criteria for loop performance
after the actual tuning.

A

b. A response to setpoint change that provides a quarter-amplitude decay
reaction curve is preferred.

40
Q

What is the benefit of selector control?
a. It allows a process limit to be exceeded in an abnormal operation.
b. It eliminates the need for external reset on PID algorithms.
c. It allows a process to operate closer to the optimum operating point.
d. It eliminates the variability in a control loop.

A

c. It allows a process to operate closer to the optimum operating point.

41
Q

Cavitation occurs in liquid flow when
a. gas and vapor flow become sonic and the flow rate drops.
b. mixtures of fluid and vapor cause erosion of the valve and pipe surfaces.
c. fluid pressure drops below the liquid’s vapor pressure and the vapor pressure
is below the outlet pressure.
d. fluid pressure drops below the liquid’s vapor pressure and the vapor pressure
is above the outlet pressure.

A

c. fluid pressure drops below the liquid’s vapor pressure and the vapor pressure
is below the outlet pressure.

42
Q

Which of the following statements is TRUE regarding controller tuning from open
loop tests?
a. The data is valid at multiple operating points.
b. The process can be approximated with a first order plus dead time model.
c. Measurement noise may obscure the results of the test.
d. The normal process operations may be interrupted for testing.

A

c. Measurement noise may obscure the results of the test.

43
Q

Cavitation is typically NOT caused by which of the following?
a. Internal recirculation
b. Air temperature
c. Flow turbulence
d. Vaporization

A

b. Air temperature

44
Q

Which of the following lists the standard range of pressure determined to represent
the lower and upper range values for the input signal?
a. 0 to 10 psi
b. 0 to 15 psi
c. 3 to 10 psi
d. 3 to 15 psi

A

d. 3 to 15 psi

45
Q

In a simple complete measurement and control loop, the current output from the
controller is sent to what element on the control side?
a. Flapper and nozzle or pilot valves
b. I/P current coil
c. 250 ohm transistor
d. Transmitter

A

b. I/P current coil