Control system fundamentals quiz

Question 1

T or F

Controls for the air handling system and zones are specifically designed for a building by the Service Technician responsible for the building. The controls are usually installed at the job site.

Answer 1

F

Question 2

T or F

The control system for a commercial building comprises many control loops and can be divided into central system and local- or zone-control loops.

Answer 2

T

Question 3

T or F

Dehumidification is generally required only during the cooling season.

Answer 3

T

Question 4

T or F

Ventilation air must be kept at the minimum required level except when used for free cooling

Answer 4

T

Question 5

T or F

For satisfactory environmental conditions, the relative humidity of the air should be 40 to 70 percent.

Answer 5

F

Question 6

T or F

An exhaust-air system may not be incorporated into main air conditioning unit

Answer 6

F

Question 7

T or F

HVAC control loop applications generally use three types of control loops

Answer 7

F

Question 8

T or F

An open-loop system does not take into account changing space conditions from internal heat gains, infiltration/exfiltration,solar gain, or other changing variables in the building

Answer 8

T

Question 9

T or F

A open-loop system relies on measurement of the controlled variable to vary the controller output

Answer 9

F

Question 10

T or F

Pneumatic, electromechanical, and electronic systems perform limited, predetermined control functions and sequences. Microprocessor-based controllers use digital control for a wide variety of control sequences.

Answer 10

T

Question 11

T or F

Two-position control is used to energize and deenergize electric strip heaters.

Answer 11

T

Question 12

T or F

in basic two-position control, the presence of lag causes the controller to correct a condition that is taking place or is about to take place, rather than one that has already passed.

Answer 12

F

Question 13

T or F

Step control uses a digital signal to attempt to obtain a digital output from equipment that is typically either on or off.

Answer 13

F

Question 14

T or F

The throttling range of a proportional control is the amount of change in the controlled variable required for the controller to move the controlled device through its full operating range.

Answer 14

T

Question 15

T or F

Process lag is the time delay between the introduction of a disturbance and the point at which the controlled variable begins to respond.

Answer 15

T

Question 16

T or F

The sensing element in a temperature sensor can be a bimetal strip, a rod-and-tube element, a sealed bellows, a sealed bellows attached to a capillary or bulb, a resistive wire, or a thermistor.

Answer 16

T

Question 17

Define control point in a controls system:

a) A calculation method that produces a control output by operating on an error signal or a time series of error signals
b) Control action that results in a change of the manipulated variable. Initiated when the controlled variable deviates from setpoint.
c) The actual value of the controlled variable
d) The quantity or condition that is measured and controlled

Answer 17

C

Question 18

Define droop in a controls system:

a) A sustained deviation between the control point and the setpoint in a two-position control system caused by a change in the heating or cooling load.
b) A simple two-position control system in which the device being controlled is either full on or full off with no intermediate operating positions available. Also called “two-position control”.
c) An action that adjusts by minute increments and decrements.
d) The quantity or condition regulated by the automatic control system to cause the desired change in the controlled variable.

Answer 18

A

Question 19

Define proportional control in a controls system:

a) Control method in which a multiple-switch assembly sequentially switches equipment (e.g., electric heat, multiple chillers) as the controller input varies through the proportional band. Step controllers may be actuator driven, electronic, or directly activated by the sensed medium (e.g., pressure, temperature).
b) An energy conservation technique that allows temperatures to float between selected settings, thereby preventing the consumption of heating or cooling energy while the temperature is in this range
c) A control algorithm or method in which the final control element moves to a position proportional to the deviation of the value of the controlled variable from the setpoint.
d) A control circuit that operates on air pressure and uses a mechanical means, such as a temperature-sensitive bimetal or bellows, to perform control functions, such as actuating a nozzle and flapper or a switching relay. The controller output usually operates or positions a pneumatic actuator, although relays and switches are often in the circuit

Answer 19

C

Question 20

Which statement is false?

a) While heat pumps are usually direct expansion, a large heat pump may be in the form of a chiller.
b) Chilled water control is usually proportional, whereas control of an evaporator coil is two­ position.
c) In direct expansion systems having more than one coil, a main valve controls a solenoid valve for each coil and the compressor is cycled by a refrigerant pressure control
d) Absorption refrigeration systems, which use heat energy directly to produce chilled water, are sometimes used for large chilled water systems

Answer 20

C

Question 21

Which statement is false?

a) Viscous coated filters remove fine particles by using the turbulence present in the air stream to drive particles to the fibers of the filter surface.
b) Filters are selected according to the degree of cleanliness required, the amount and size of particles to be removed, and acceptable maintenance requirements.
c) Electrostatic filter plates may be coated with an adhesive
d) A ventilation system that uses return air is more common than the 100 percent outdoor air system

Answer 21

A

Question 22

Which statement is false?

a) Automatic control systems use feedback to reduce the magnitude of the deviation and produce system stability.
b) Self-powered systems are a type of control that use the power of the measured variable to induce the necessary corrective action
c) In a pneumatic controller, the sensor sends the controller a continuous signal
d) The controller samples digital data at set time intervals, rather than reading it continually. The sampling method is called pulsive control signaling

Answer 22

D

Question 23

Which statement is false?

a) In many of the larger commercial control systems, an electronic-pneumatic transducer converts the pneumatic output to a variable pressure output for pneumatic actuation of the final control element.
b) The most common forms of energy for automatic control systems are electricity and compressed air.
c) The result of using a basic two-position control is cyclical operation of the controlled equipment and a condition in which the controlled variable cycles back and forth between two values (the on and off points) and is influenced by the lag in the system.
d) Traditionally, analog devices have performed HVAC control.

Answer 23

A

Question 24

Control systems use different control modes to accomplish their purposes. Control modes in commercial applications include:

a) two-position, step, and floating control; proportional, proportional-integral, and proportional-integral-derivative control; and adaptive control.
b) two-position, step, and floating control; proportional, secondary input control, proportional-integral-derivative control; and adaptive control.
c) floating control, corrective signal, proportional, proportional-integral, proportional-integral-derivative control; and adaptive control.
d) two-position, step, and floating control; proportional, mandarin orange induction control, proportional-integral-derivative control; and adaptive control.

Answer 24

A

Question 25

Which statement is true?

a) In a heating system, the heat anticipator is connected so that it de-energizes whenever the bimetal element calls for heat
b) Heat anticipation raises the control point as the heat requirement increases.

c) The ideal method of controlling the temperature in a space is to replace lost heat or displace gained heat in exactly the amount needed. With basic two-position control, such exact operation is possible because the heating or cooling system is either full on or full off and the delivery at any specific instant
is either too much or too little.

d) In timed two-position control, the controller responds to gradual changes in the average value of the controlled variable rather than to cyclical fluctuations.

Answer 25

D

Question 26

Which statement is true?

a) Time proportioning control provides more effective two­ position control than heat anticipation control.
b) With time proportioning control, heat is introduced into the space using on/off cycles based on the anticipated heat load on the building and programmable time cycle settings.
c) In electromechanical thermostats, the total cycle time setting is determined primarily by the lead of the system under control
d) Time proportioning control is not recommend for electric heat control

Answer 26

A

Question 27

A floating control ______.

a) requires a fast moving actuator
b) is a variation of two-position control
c) is used primarily for intake control systems where the sensor is immediately upstream from the coil
d) keeps the control point near the setpoint and works correctly only with a constant load level

Answer 27

B

Question 28

In a typical floating static pressure application, _____________ .

a) a drop in static pressure below the controller setpoint causes the actuator to drive the damper toward· closed.
b) the control point can not float between open and closed limits
c) the narrow differential of the controller stops the actuator after it has moved a short distance.
d) When the control point moves out of the deadband, the actuator moves the controler toward open or closed until the control point moves into the deadband again.

Answer 28

C

Question 29

An example of compensation control would be _____________ .

a) the discharge temperature resetting the outdoor temperature of a fan system so that the outdoor temperature increases as the discharge temperature decreases
b) the outdoor temperature resetting the discharge temperature of a fan system so that the discharge temperature increases as the outdoor temperature decreases
c) the discharge temperature resetting the mass spectromatic temperature of a fan system so that the discharge temperature increases as the outdoor temperature increases
d) the outdoor temperature resetting the discharge temperature of a fan system so that the discharge temperature decreases as the outdoor temperature increases

Answer 29

B

Question 30

Compensation control can ______________ .

a) assist when control is required if a workplace injury has occured
b) neither increase or decrease the setpoint as the compensation input increases
c) reset the controller primary sensor setpoint
d) increase the setpoint by removing compensation on an decrease in the compensation variable.

Answer 30

C

Question 31

Which statement is false?
With a PID control, ________ .

a) if the control point moves away from the setpoint, the derivative function outputs a corrective action to bring the control point back more quickly than through integral action alone.
b) derivative function directly follows any change and is proportional to the rate of change
c) if the control point moves toward the setpoint, the derivative function reduces the corrective action to slow down the approach to setpoi:nt, which reduces the possibility of overshoot.
d) derivative function to PI control is added

Answer 31

B

Question 32

Which statement is false?

_________ contribute to measurement lag.

a) Dynamic error
b) Reproducibility
c) Velocity error
d) Dead zone

Answer 32

C

Question 33

Which statement is false?

a) A capacitance that is large relative to the control agent tends to keep the controlled variable constant despite load changes.
b) Capacitance differs from capacity.
c) It takes less time to raise the temperature of a cubic foot of water one degree· than a cubic foot of air.
d) A large capacitance is good to have, but also makes changing the system variable to a new value more difficult

Answer 33

C

Question 34

Which statement is false?

In a rod-and-tube element, _____________ .

a) the bellows and capillary also sense temperature, but because of their small volume compared to the bulb, the bulb provides the control.
b) the technology can be replaced by electronic temperature controllers use low-mass sensing elements that respond quickly to changes in the controlled condition.
c) four specialized versions of the remote bulb controller are available.
d) the remote bulb is placed in the controlled medium where changes in temperature cause changes in pressure of the fill.

Answer 34

C