Modules 4 & 5

Question 1

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.

Answer 1

c. The components may be physically separated.

Question 2

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.

Answer 2

b. Moderate disturbances during the testing can be tolerated.

Question 3

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

Answer 3

d. Proportional, integral, and derivative modes on error

Question 4

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

Answer 4

c. Pneumatic

Question 5

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

Answer 5

a. +/– 10 V

Question 6

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

Answer 6

b. Accuracy

Question 7

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

Answer 7

c. Failure thresholds

Question 8

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.

Answer 8

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

Question 9

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.

Answer 9

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

Question 10

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.

Answer 10

b. overcome packing friction.

Question 11

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.

Answer 11

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

Question 12

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.

Answer 12

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

Question 13

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.

Answer 13

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

Question 14

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.

Answer 14

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

Question 15

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.

Answer 15

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

Question 16

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.

Answer 16

d. improve response of the control loop.

Question 17

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

Answer 17

b. scheduled tuning.

Question 18

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

Answer 18

b. Fail-safe mode of the valve

Question 19

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.

Answer 19

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

Question 20

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

Answer 20

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

Question 21

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

Answer 21

b. Manual-automatic switching

Question 22

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.

Answer 22

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

Question 23

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

Answer 23

c. Butterfly

Question 24

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

Answer 24

b. Bridle position for the highest speed permitted

Question 25

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.

Answer 25

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

Question 26

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.

Answer 26

b. increase.

Question 27

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

Answer 27

b. establishes the setpoint for the secondary loop controller.

Question 28

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.

Answer 28

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

Question 29

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

Answer 29

b. Gain

Question 30

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

Answer 30

c. 16 mA span and 4 mA live zero

Question 31

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.

Answer 31

b. derivative-on-measurement.

Question 32

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.

Answer 32

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

Question 33

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.

Answer 33

b. calculating the valve sizing coefficient.

Question 34

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.

Answer 34

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

Question 35

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

Answer 35

c. 12 mA

Question 36

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

Answer 36

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

Question 37

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.

Answer 37

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

Question 38

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

Answer 38

b. Butterfly

Question 39

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.

Answer 39

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

Question 40

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.

Answer 40

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

Question 41

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.

Answer 41

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

Question 42

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.

Answer 42

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

Question 43

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

Answer 43

b. Air temperature

Question 44

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

Answer 44

d. 3 to 15 psi

Question 45

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

Answer 45

b. I/P current coil