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127 Cards in this Set
- Front
- Back
Common indicators necessary for proper process operation may include:
a) interlocks and permissives b) low water cutoffs, flame scanners and safety values c) programmable logic controls d) pressure, valve position, and conductivity measurement devices e) pneumatic, hydraulic, and electrical switches |
d) pressure, valve position, and conductivity measurement devices |
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In an automatic control system the controller output changes the position of the:
a) recorder b) transmitter c) sensing element d) final control element e) indicator dial |
d) final control element |
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A "control" should be considered as a special device which:
a) sends or transmits a positive rather than negative signal b) tries to maintain a set point c) is logic device capable of making decisions d) notifies operators of errors or faults in a system e) leaves a hard-copy record of a system's performance |
b) tries to maintain a set point |
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The major elements needed to construct automatic control loop instrumentation systems includes a sensing element, a ____________, a controller and a control valve.
a) recorder b) resistance c) transmitter d) manometer e) float cage |
c) transmitter |
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In a "closed loop" system of control, the control will change:
a) automatically b) both automatically and manually c) manually d) intermittently e) inversely to the sign |
a) automatically |
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A control loop controller:
a) does not require a set point value b) sends a signal to a primary element c) measures the manipulated variable value, eliminating the need of a primary element d) will always eliminate deviation e) constantly compares input signals to the set point |
e) constantly compares input signals to the set point |
|
An open loop control system requires:
a) a transducer and a recorder b) minimum deviation from set point c) a very small amount of dead time or lag d) constant attention e) two final control elements |
d) constant attention |
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The means commonly used as medium of control in a plant include: hydraulic, mechanical, pneumatic and:
a) physical b) electrical c) manual d) thermal e) magnetic |
b) electrical |
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When a current signal is used for signal transmission it is a/an:
a) AC signal b) ampere signal c) power signal d) generated signal e) DC signal |
e) DC signal |
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A sensing element sends its signal to the:
a) controller b) recorder c) control valve d) transducer e) transmitter |
a) controller |
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When a process variable has no method of sending information to the final control element the system is known as:
a) an automatic system b) an open loop system c) a cascading system d) a feedback system e) a feed forward system |
b) an open loop system |
|
A sensing element receives its signal from the:
a) controller b) recorder c) control valve d) transducer e) controlled variable |
e) controlled variable |
|
A common air pressure range for pneumatic control systems is:
a) 3 to 15 kPa b) 20 to 100psi c) 20 to 30 kPa d) 40 to 60 psi e) 20 to 100 kPa |
e) 20 to 100 kPa |
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The fire eye or flame scanner keeps a burner circuit energized as long as the burner flame is maintained through the use of a:
a) final control element b) manipulated variable c) recorder d) sensing element e) photoelectric transducer |
e) photoelectric transducer |
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A device which will cause a visible light signal to become an instrument analog signal is the:
a) photoelectric transducer b) transmitter c) controller d) final element e) current-to-pneumatic transducer |
a) photoelectric transducer |
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Some of the components required to construct an automatic control loop are a sensing element, a transmitter, a __________, and a control valve.
a) controller b) transformer c) transducer d) piping system e) converter |
a) controller |
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When a process variable has no method of sending information to the final control element the system is know as:
a) an automatic system b) an open loop system c) a cascading system d) a feedback system e) a feed forward system |
b) an open loop system |
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A sensing element receives its signal from the:
a) controller b) recorder c) control valve d) transducer e) controlled variable |
e) controlled variable |
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The fire eye or flame scanner keep a burner circuit energized as long as the burner flame is maintained through the use of a:
a) final control element b) manipulated variable c) recorder d) sensing element e) photoelectric transducer |
e) photoelectric transducer |
|
A device which will cause a visible light signal to become an instrument analog signal is the:
a) photoelectric transducer b) transmitter c) controller d) final element e) current-to-pneumatic transducer |
a) photoelectric transducer |
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Some of the components required to construct an automatic control loop are a sensing element, a transmitter, a __________, and a control valve.
a) controller b) transformer c) transducer d) piping system e) converter |
a) controller |
|
A thermocouple measures:
a) pressure b) temperature c) flow d) velocity e) light |
b) temperature |
|
When measuring atmospheric pressure with a barometer, the practical fluid to use is:
a) mercury b) oil c) steam d) nitrogen e) alcohol |
a) mercury |
|
Relative to flow, velocity is kinetic energy and when velocity increases, the:
a) pressure and potential energy, will also increase b) cross-sectional area of the piping will be increased c) the mass quantity flowing per second will decrease d) potential energy in the form of pressure will decrease e) density will decrease |
d) potential energy in the form of pressure will decrease |
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If the boiler pressure increases then, in the pressure gauge, the:
a) bourdon tube will tend to straighten b) spring will compress more c) bourdon tube will become less circular in cross-section d) bourdon tube will become smaller in diameter e) bourdon tube will tend to twist |
a) bourdon tube will tend to straighten |
|
Thermocouples require:
a) a non-metallic strip or coil b) a thermopile c) two dissimilar metals d) an elliptical sectioned tube e) a heating element |
c) two dissimilar metals |
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One of the most widely used process variables in a system is:
a) temperature b) pressure c) density d) purity e) flow |
e) flow |
|
Liquid must be in its vapour form:
a) in order to measure density b) if purity is to be measured c) when a chromatograph is being used d) when conductivity e) when resistance or reluctance is being measured |
c) when a chromatograph is being used |
|
The electrical output from a thermocouple is measured by a:
a) milliampmeter b) wattmeter c) milliwattmeter d) millivoltmeter e) power meter |
d) millivoltmeter |
|
The advantage of using a venturi tube, rather than an orifice plate for flow measurement is that it:
a) produces less permanent pressure loss b) costs less to install c) produces more pressure drop d) is less bulky e) is flexible |
a) produces less permanent pressure loss |
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Calculate the height in meters between the water surface in an elevated tank and the ground to create a pressure of 335kPa.
a) 13.13 m b) 18.43 m c) 34.15 m d) 37.087 m e) 39.936 m |
c) 34.15 m
P = g*p*h Therefore, P / g p = h 335kPa / 9.81m/s^2 / 1 kg/m^3 = 34.15m
P= pressure g = acceleration due to gravity, (9.81m/s^2) p = density, (fresh water, 1 kg/m^3) h = height, meters |
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A two-position controller compares conditions to a set point and:
a) will start or stop a process b) desired value c) will modulate the final element d) can automatically readjust the set point e) will maintain final element position at 50% |
a) will start or stop a process |
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Solenoid operated valves open when an electric current flows through a __________ of wires producing a magnetic field.
a) coil b) resistance c) strand d) pair e) dissimilar pair |
a) coil |
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When controller output is proportional to the amount of error (or deviation), the controller is:
a) derivative only b) integral c) two-piston d) proportional plus reset plus rate e) proportional |
e) proportional |
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A proportional controller: (choose all that apply)
[a] may have a pneumatic or electronic analog output [b] provides a proportional output based on the error between process variable and set point [c] requires no operator input [d] provides on/off control [e] is typically something the operator cannot touch |
[a] may have a pneumatic or electronic analog output [b] provides a proportional output based on the error between process variable and set point |
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A control valve:
a) is always normally closed b) is a form of variable resistance in a piping system c) is nearly always reverse acting d) must be part of a cascade control system e) can, by itself, be part of a split range control loop |
b) is a form of variable resistance in a piping system |
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Putting a controller in "manual" control means:
a) the operator selects the controller output b) the controller output responds to a process variable c) there is no control of the final control element d) a man must stand beside the value for safety reasons e) the plant is about to shut down |
a) the operator selects the controller output |
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Cascade control entails the use of:
a) one controller, one transmitter, two valves b) one controller, two transmitters, two valves c) two controllers, one transmitter, two valves d) two controllers, two transmitters, two valves e) two controllers, two transmitters, one valve |
e) two controllers, two transmitters, one valve |
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Each pen in a multi-pen strip chart recorder is operated by a different:
a) sensor b) transmitter c) recorder d) controller e) process |
b) transmitter |
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A control valve that has one plug that moves upward to close the port is called:
a) reverse acting single ported b) double seated direct acting c) reverse acting diaphragm actuated d) direct acting single ported e) electrically operated |
a) reverse acting single ported |
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A proportional only controller:
a) cannot maintain maximum value of the final element b) signal output varies directly with set point error (or deviation) c) can be compared to the cruise control on an automobile d) will maintain measured variable at set point e) will respond fully when deviation is high |
b) signal output varies directly with set point error (or deviation) |
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A process variable which is adjusted in order to maintain or achieve some desired value of another variable is termed the:
a) process variable b) final variable c) manipulated d) controlled variable e) transmitting variable |
c) manipulated |
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When a float is used for measuring level, and installation within a vessel is impractical, a device often used is the:
a) float manometer b) float cage c) differential head meter d) diaphragm e) head transmitter |
b) float cage |
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An inclined manometer is commonly used:
a) when very low pressures or vacuums are being measured b) to measure high pressure differentials c) in conjunction with a flexible rubber diaphragm d) when reading accuracy is not critical e) for measuring level |
a) when very low pressures or vacuums are being measured |
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When a diaphragm devise is used for boiler water level measurement, the boiler pressure is compensated for or off-set by:
a) using a bellows on the HP side b) a spring which balances the differential pressure c) applying the pressure to both sides of the diaphragm d) reversing the reference and variable legs e) joining the reference and variable legs upstream of the device |
c) applying the pressure to both sides of the diaphragm |
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The Bourbon tube is often shaped in the form of a "C", having an arc span of about:
a) 180 degrees b) 360 degrees c) 200 degrees d) 90 degrees e) 270 degrees |
e) 270 degrees |
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A bimetal thermometer reacts to changes of:
a) pressure b) flow c) humidity d) heat e) temperature |
e) temperature |
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Temperatures are measured by:
a) wattmeters b) bourdon tubes c) thermowells d) pressure differential e) thermocouples |
e) thermocouples |
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When a basic differential pressure transmitter is used for flow measurement:
a) the low pressure side is upstream of the orifice plate b) the transmitter sends a signal directly to the final control element c) output signal varies with the flow d) movement of the force bar towards the nozzle will increase air bleed e) air supply pressure varies with the flow |
c) output signal varies with the flow |
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In a basic pneumatic transmitter, movement of the flapper towards the nozzle will:
a) increase the nozzle bleed b) change the size of the supply orifice c) maintain steady transmitter supply pressure d) change transmitter supply pressure e) increase feedback bellows pressure |
e) increase feedback bellows pressure |
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The common "modulating" control modes for a plant control system controller are:
a) integral and derivative b) proportional and reset c) proportional, rest, and integral d) reset, integral, and rate e) derivative, proportional, and integral |
e) derivative, proportional, and integral |
|
Integral and Derivative functions are:
a) additions to all proportional controllers b) also called right and reset controllers c) an aid to improving effectiveness of the process controller d) used in on/off control e) integral to derivatives |
c) an aid to improving effectiveness of the process controller |
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A circular chart recorder:
a) provides a different function to a strip chart b) is a later design than a strip chart c) may incorporate a bourdon tube d) does not provide a permanent record e) is used on a computer screen |
c) may incorporate a bourdon tube |
|
A flapper-nozzle assembly is basic to all:
a) controllers b) pneumatic transmitters c) recorders d) pneumatic devices e) actuators |
b) pneumatic transmitters |
|
A pneumatically actuated globe type control valve which opens upon air failure:
a) could have a direct acting actuator and a direct acting valve b) could have a direct acting actuator and a reverse acting valve c) could have a reverse acting actuator and a direct acting valve d) must be used on emergency shutdown e) is not used in a power plant |
a) could have a direct acting actuator and a direct acting valve |
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Low water fuel cut-offs should shut the fuel off if the water level drops below:
a. the lowest permissible level b. the fire line c. the lowest visible water level d. 25 mm above the bottom of the gauge glass e. below the tops of the tubes in the top row of tubes |
d. 25 mm above the bottom of the gauge glass |
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A low-water cut-off switch should close the automatic fuel valve(s) when the water is:
a. at the lowest permissible water line b. at the lowest visible water line c. 1 to 2.0 cm above the bottom gauge glass nut d. 1 to 2.0 cm below the gauge glass nut e. 76 mm above the lowest permissible water line |
e. 76 mm above the lowest permissible water line |
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Modulating combustion control will
a) change air and fuel flow proportionally to steam pressure change |
a) change air and fuel flow proportionally to steam pressure change |
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A packaged steam boiler modulating combustion control system will routinely
a) maintain drum level within a desired range |
e) maintain boiler steam pressure within a desired range |
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Single element feedwater control systems are very efficient in maintaining the boiler water level when:
a. the boiler has a large water capacity b. the boiler is a fire tube boiler c. the fluctuations in load are slow and small d. load demands are low e. the boiler is gas fired |
c. the fluctuations in load are slow and small |
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The low water fuel cut-off:
a. shuts off the water flow if the fuel pressure is low b. shuts off the fuel if the water pressure is too low c. shuts off the fuel if the water level is too low d. controls the water level in the boiler e. shuts off the fuel and water supply |
c. shuts off the fuel if the water level is too low |
|
A hot water boiler low-water fuel cutoff
a) should be tested weekly during routine boiler operation |
b) cannot be tested during routine boiler operation |
|
An advantage of the "electric probe" type low water-off is:
a. it can be incorporated on any size or type of boiler b. it is simple in design with no moving parts c. scale or sediment will not hinder its operation d. all moving parts are easily accessible for cleaning and inspection e. the probes will indicates a level even if not completely covered by water |
b. it is simple in design with no moving part |
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An automatic boiler ON-OFF or operating control switch has an adjustment for cut-in or cut-out value and another for
a) a differential between the two b) manual or automatic control |
a) a differential between the two
|
|
A mercury switch bulb is under high vacuum and contains inert gas
a) so it will not explode |
b) to prevent corrosion of the contacts |
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The drain of a hot water boiler low-water fuel cutoff should be opened to flush out any debris
a) annually |
c) weekly |
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The boiler must be equipped with a seconds low water cut-off when:
a. the boiler has over 47 m^2 heating surface b. the boiler has duel fuels c. the first device is also used to control the feedwater flow d. the boiler uses coal as fuel e. the boiler has two burners |
c. the first device is also used to control the feedwater flow |
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Two element feedwater controls:
a. measures water level and steam flow b. compares forced draft to water level c. compares fuel flow to steam flow d. has one element in the feed control valve and one element in the deaerator e. compares water level to the firing rate |
a. measures water level and steam flow |
|
A float operated level control
a) will recognize swell and shrinkage and correct the feedwater flow |
c) is often used on small boilers |
|
Modulating burner controls operate by regulating:
a. steam and fuel flow b. fuel temp and air flow c. fuel flow, air flow and feedwater pressure d. fuel and air flow e. fuel and atomizing steam flow |
d. fuel and air flow |
|
Modulating combustion control on a heating boiler is accomplished by
a) shutting down or lighting up the burner as pressure or |
c) changing the amount of fuel and air to the burner |
|
The purpose of a low water fuel cut-off is to
a) shut off the feedpump when the water level gets too high |
e) shut off the fuel supply when the water level gets too low |
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The low water fuel cut off:
a. shuts of the water flow if the fuel pressure is low b. shuts off the fuel if the water pressure is low c. shuts off the fuel if the water level is too low d. controls the water level in the boiler e. shuts off the fuel and water supply |
c. shuts off the fuel if the water level is too low |
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A thermo-hydraulic feedwater regulator uses ______ as mediums.
a. oil and nitrogen b. CO2 c. water and steam d. mercury and zinc e. air and water |
c. water and steam |
|
The float chamber of the low water cut-off is blown out often to prevent
a) the chamber collecting sediment |
a) the chamber collecting sediment |
|
The most reliable method of checking or testing a low-water fuel cut off is to
a) manually trip the cut-off linkage to shut off the burner |
c) lower the water in the boiler to the level where the burner should cut out |
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A low water fuel cut-off may be activated by
a) lowering the water level in the boiler |
a) lowering the water level in the boiler |
|
The drain of a hot water boiler low-water fuel cutoff should be opened to flush out any debris
a) annually |
c) weekly |
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The main controlling device used with an on/off combustion fuel control, is a _________ sensing element.
a. pressure b. level c. temperature d. electronic e. pneumatic |
a. pressure |
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An interrupted pilot:
a) burns continuously, like that in a home furnace |
d) lights, completes a trial, and extinguishes after a main |
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The programmer will go through a post purge:
a. only if the pilot fails to ignite b. only on flame failure c. by manual involvement d. on any type of shutdown except by power loss e. on routine shutdown only
|
d. on any type of shutdown except by power loss |
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If during startup the pilot fails to ignite a lockout switch will be energized:
a. after a trial period of 15 to 30 seconds b. immediately c. within 4-5 seconds d. after the flame relay de-energizes e. after the main burner flame ignites |
a. after a trial period of 15 to 30 seconds |
|
A programming control timer may consist of a motor and a:
a. series of clocks: b. number of leak off chambers c. number of cams and switches d. number of tubes e. series of relays |
c. number of cams and switches |
|
During a programmed start-up if an ignitor spark is visible but no flame appears the operator should suspect
a) a boiler low water level |
c) the pilot manual fuel valve is closed |
|
Boiler furnaces are purged
a) so that the programmer has time to verify permissiveness of interlocks |
d) so that combustibles are fully removed prior to ignition |
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Automatic boiler liquid fuel manual valves should be opened
a) prior to pre-purging |
a) prior to pre-purging |
|
The operating pressure control will control the
a) steam pressure in the boiler |
a) steam pressure in the boiler |
|
On a gas fired automatic boiler a normal programmed start-up takes approximately
a) 105 seconds |
a) 105 seconds |
|
Automatic boiler programming controls
a) must incorporate a modulating control system |
c) require an ON-OFF or two-position control switch |
|
On a boiler with high-low fire control, if the burner stays on "low fire":
a. the modulating control may have failed b. the igniter is defective c. the safety lockout needs to be reset d. the low air pressure switch has opened e. the programmer is stuck in the pre-purge phase |
a. the modulating control may have failed |
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If a shutdown occurs during normal firing of a boiler and the steam pressure is below the normal cut-out value, the problem could be:
a. the sensing line to the combustion air proving switch has broken b. main flame trail failure c. pilot flame trial failure d. igniter transformer failure e. high steam pressure limit switch tripped |
a. the sensing line to the combustion air proving switch has broken |
|
Automatically fired boilers with restart:
a. when a lockout switch has been activated b. when water level has been re-established c. when power fails d. if a flame failure has been detected e. when the operator has completed the purge |
b. when water level has been re-established |
|
Desktop, laptop and handheld computers are examples of:
a. minicomputers b. macrocomputers c. mainframes d. microcomputers e. multicomputers |
d. microcomputers |
|
An analog control loop output must be put through a/an ___________ before the computer can react to the signal.
a. analog to digital converter b. signal inverter c. ROM detector d. modem e. CPU |
a. analog to digital converter |
|
A digital input computer is protected from harmful voltages by means of:
a. splitter bars b. fuses c. isolating circuits d. circuit breakers e. stand-alone devices
|
c. isolating circuits |
|
The main function of a mainframe computer system is to:
a. evaluate systems by comparison b. rapidly process large amounts of data c. perform only a specific dedicated task d. produce "hypothetical" solutions to problems e. act as a networking switch |
b. rapidly process large amounts of data |
|
Hard drives are often backed up by copying their information to:
a. printers b. removable media c. plotters d. registers e. strip charts |
b. removable media |
|
Sharing and transferring information between computers is termed:
a. analoging b. multiplexing c. plotting d. number crunching e. networking |
e. networking |
|
Which of the following is true with regards to computer networks?
a. the network will function when a computer fails b. they are not as fast as older mainframe computers c. a minicomputer is required as a server d. They are always connected by hardwire connections e. They require large air conditioned rooms |
a. the network will function when a computer fails |
|
Which of the following computer program language is considered a "high level language"?
a. English b. WordPerfect c. Desktop publishing d. Latin e. Pascal |
e. Pascal |
|
The second element of a two element feedwater control system compensates for, or offsets:
a) level variation b) differential feedwater pressure c) differential steam flow rate d) feedwater temperature variation e) shrink and swell |
e) shrink and swell |
|
Overheating of boiler heating surfaces due to low water:
a) is the main cause of boiler failure b) will cause a furnace explosion c) can be eliminated with a low-water fuel cut-off d) cannot occur if the boiler is a hot water unit e) can be prevented with proper water treatment |
a) is the main cause of boiler failure |
|
A float operated low-water fuel cut-off has its switch separated from boiler pressure by:
a) a float cage b) a mercury envelope c) a flexible diaphragm d) siphon e) packing |
c) a flexible diaphragm |
|
With single element feedwater control the level transmitter output is:
a) received by a final element b) proportional to drum level c) sent to a selector station d) constant regardless of level e) a function of steam flow |
b) proportional to drum level |
|
An intermittent pilot on an automatic boiler:
a) burns continuously, lie that in a home furnace b) lights before the main burner and goes out with it c) is one which has been extinguished by a flame scanner d) lights, completes a trial, and extinguishes after a main flame trial e) must be manually ignited |
b) lights before the main burner and goes out with it |
|
At the end of the prepurge the timer:
a) shuts down b) open the fuel valve c) opens the pilot valve d) goes through an ignition trial e) energizes the ignition transformer |
e) energizes the ignition transformer
|
|
Before lighting off a boiler you should always purge the furnace in order to:
a) prove that the furnace and stack are clear b) blow out any soot which may have collected in the tubes c) cool the furnace so that premature combustion can occur d) dry out the brickwork and check for leaks e) remove any combustible gases which may have collected |
e) remove any combustible gases which may have collected |
|
Computer information can be stored on a: (Choose all that apply)
[a] DVD [b] CD [c] hard drive [d] CPU |
[a] DVD [b] CD [c] hard drive |
|
A device used to convert audio tones to computer language is commonly known as a:
a) transmitter b) multiplexed c) dot matrix d) modulator/demodulator e) CPU |
d) modulator/demodulator |
|
A disk drive in a computer system is used to:
a) hide information b) transfer information to the modem c) print information d) store information e) transfer information to another floppy disk |
d) store information |
|
Computer "soft keying" is:
a) done only with lap top units b) down to make the computer quicker and easier to use c) a method of pressing a key twice before a result is obtained d) the same as using a mouse of joystick e) a system used to tint graphics |
b) down to make the computer quicker and easier to use |
|
The main component of any computer, is the:
a) keyboard b) screen c) modem d) printer e) central processing unit |
e) central processing unit |
|
Inputs for logic and supervisory computer functions are mainly:
a) by switch contacts b) actions of an operator using the keyboard c) stored on a disk which is required for operation d) controlled by relays e) non-decision making |
a) by switch contacts |
|
A device used to convert audio tones to computer language is commonly known as a:
a) transmitter b) multiplexed c) dot matrix d) modulator/demodulator e) CPU |
d) modulator/demodulator
|
|
Transmitters, which transmit digital codes directly to a computer, are known as:
a) digital transmitters b) smart transmitters c) analog transmitters d) pneumatic transmitters e) AND-OR devices |
b) smart transmitters |
|
Computer "Rum Time Totals" are commonly used:
a) in graphic displays b) for inventory control c) for logic supervisory systems d) for maintenance management e) with a MODEM |
d) for maintenance management |
|
The type of circuit used to store (write) and retrieve (read) information from a computer is known as its:
a) Menu b) CRT c) RAM d) CPU e) ROM |
c) RAM |
|
The apparatus which converts current signals to pneumatic and pneumatic to current signals is called a |
d) transducer |
|
A chromatograph uses electronic devices which
a) utilize electrical current as a measurement base |
b) have inverse resistance properties relative to |
|
A strain gauge can be used to measure:
a. stresses in pipe walls b. pressure in boilers c. forces on a column d. the densities of materials e. the tension given by a compressive load |
c. forces on a column |
|
A "U" tube manometer may be filled with:
a. granular substance b. nitrogen c. heavy oils d. a gaseous mixture e. light oils |
e. light oils |
|
A helix strip bimetallic thermometer is wound spirally to:
a. dampen the motion b. ease the installation c. increase range of temperature measurement d. amplify the motion e. retard the expansion of the strip |
d. amplify the motion |
|
The constant head connection in a remote water level indicator is made to the:
a. feed water pump discharge b. water space c. atmosphere d. feed water regulating valve e. steam space
|
e. steam space |
|
The inclined "U" tube manometer:
a. will measure pressure in kPa b. can only be used with mercury c. is more accurate than the "u" tube manometer d. has two furnace connections e. is more difficult to read |
c. is more accurate than the "u" tube manometer |
|
Control Valves:
a.consist of a valve body and accommodator b. react to controller input c. provide a fixed resistance to flow d. have one major component e. require a pressure drop across the valve to maintain flow |
e. require a pressure drop across the valve to maintain flow |
|
A recorder utilizing a spiral Bourdon tube will have a pen movement:
a. linear to the tube travel b. proportional to the change in the tube pressure c. angular to the tube travel d. range of 0 to 24 hours e. range of 0 to 7 days |
b. proportional to the change in the tube pressure |
|
Circular charts are normally replaced every 24 hours but some charts may rotate for up to how many days?
a. 30 b. 2 c. 7 d. 14 e. 90 |
c. 7 |