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Power Engineering > Unit 20 Basic Control loop components > Flashcards

Unit 20 Basic Control loop components Flashcards

1
Q

When a process variable has no method of sending information to the final control element, the system is known as

A

open loop

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2
Q

A variable adjusted in order to maintain or achieve a desired value of another variable is termed the

A

manipulated variable

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3
Q

The apparatus that converts current signals to pneumatic and vice versa is a

A

Transducer

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4
Q

A device that converts the measurement of a sensing device into a signal, is a

A

Transmitter

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5
Q

State the most common signal range for pneumatic instrument signals.

A

20-100kPa

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6
Q

List 2 types of electrical signals used in control systems and give an example of where each might be used

A

Voltage signals - used with switching devices eg. flame scanners, low water fuel cut off, pump controllers
Current signals- used for analog instruments where signals must be sent over long distances

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7
Q

A common example of a photoelectric transducer used on boilers is the

A

flame scanner

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8
Q

An inclined manometer is commonly used to measure

A

very low pressures or vacuums

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9
Q

In a glass stem thermometer the space above the liquid is usually

A

evacuated

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10
Q

A chromatoghraph uses electronic devices which

A

have decreased resistance as temperature rises

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11
Q

The electrical output from a thermocouple is measured by a

A

millivoltmeter

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12
Q

a device used to measure variations in atmospheric pressure is called a

A

Barometer

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13
Q

To increase the movement of a Bourdon tube without use of linkage that may cause additional error, the tube can be formed into the shape of a

A

spiral or helix

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14
Q

Name 3 types of sensing elements used to measure flow by creating a differential pressure in the pipe

A

Orifice plate, venture tube, flow nozzle

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15
Q

The pneumatic transmitter nozzle receives a constant air supply pressure of approximately?

A

140 kPa

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16
Q

When controller output is proportional to the amount of deviation, the controller is

A

Proportional

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17
Q

when an operator uses CRT or LCD displays, the computer control display

A

can stretch or compress time periods

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18
Q

A valve that seals on the downstroke is

A

direct acting

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19
Q

Why is a double seated control valve better suited to throttling action than single seated

A

Less force is required to position the control valve because the pressure of the fluid acts on the top of one seat and the bottom of the other.

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20
Q

What is the difference between and indicator and a recorder

A

An indicator shows only the current value of the process variable, whereas a recorder shows the current value and previous values to allow the operation of the process to be analyzed over time.

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21
Q

What is the main cause of heating boiler failure

A

overheating the metal surfaces due to low water level

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22
Q

What are 3 low water fuel cut-off devices

A

float type; magnetic; electric probe

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23
Q

Automatic boiler programming controls require what kind of control switch

A

on-off or multi-range

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24
Q

An interrupted pilot of an automatic boiler operates as

A

ignites, completes a trial, and extinguishes after a main flame trial

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25
Q

liquid fuel manual valves for an automatically controlled boiler should be opened when

A

prior to pre-purging

26
Q

During a programmed start-up, if an igniter spark is visible but no pilot flame appears the operator should suspect

A

a pilot manual fuel valve is closed

27
Q

State the purpose of purging the boiler furnace before igniting the pilot flame

A

To clear the furnace of any combustible gases that may have built up

28
Q

If a boiler trips on low water level or flame failure, the programming controller will shut the boiler down. What steps must the operator take before the boiler will restart

A

The initial low water level or flame failure must be corrected. the operator may need to reset the boiler

29
Q

List the ASME codes and CSA regulations regarding low water fuel cut-offs

A

ASME Code, section IV- no shut off valves placed in cut-off piping. Piping will be a min of 1”
CSA -B51 09

30
Q

A boiler control manual- automatic transfer or selector station may be used to

A

manually override automatic control loops

31
Q

Low water fuel cut-off must shut the fuel off Before the water level drops to

A

25 mm above the bottom of the gauge glass

32
Q

Modulating combustion control will change

A

air and fuel flow proportionally to steam pressure change

33
Q

According to the ASME code, explain the requirements for high pressure limit switches

A

The code states that all automatically fired steam heating boilers must have a high limit pressure activated switch that shuts off the fuel to the burner when steam pressure exceeds normal ranges

34
Q

The variable area meter consists of changing

A

area

35
Q

The main function of a mainframe computer system is to

A

rapidly process large amounts of data

36
Q

An analog control loop output must be put through a ____ before the computer can react to the signal

A

analog/digital converter

37
Q

A digital input computer is protected from harmful voltages by means of

A

isolating circuits

38
Q

Computer “run time totals” are commonly used for

A

maintenance management

39
Q

signals which have an infinite number of values between a minimum and maximum are

A

analog signals

40
Q

Digital signals have what values

A

on or off

41
Q

a manometer may be filled with what types of fluids

A

water or mercury

42
Q

What is the advantage of using an inclined manometer over a conventional U - tube manometer

A

increased accuracy

43
Q

How to know if a manometer is correctly calibrated

A

the level should be the same distance above zero in one leg, as it is below zero in the other

44
Q

What are 3 things a pressure gauge must be protected against to avoid damage while in operation

A

High temperatures - water seal
Corrosive or congealing fluids - chemical seal
vibration or pressure pulsation - damper or needle valve

45
Q

Four types of pressure sensing elements

A

Bourdon tube, Diaphragm, Bellows, strain gauge

46
Q

Three types of orifice plates

A

concentric, eccentric, and segmental

47
Q

Bernoulli’s Principle

A

As flow velocity increases static pressure is reduced

48
Q

state the upper and lower limits of the temperature measuring capabilities for mercury

A

-39 - 450 C. if the space above the mercury is pressurized with nitrogen or argon, the upper limit may be increased to 550 C

49
Q

Explain the purpose of the relay used in a pneumatic transmitter

A

The relay boosts the air pressure signal from the nozzle pressure of 14-28kPa to the output pressure of 20-100kPa

50
Q

What type of controller compares actual conditions to setpoint; and sends a variable signal to the control valve, causing it to be open, closed or somewhere in between. In addition they include action that forces the final control element to move more quickly for rapid changes in the process variable

A

Proportional plus derivative (rate) controllers

51
Q

reset or proportional plus integral controllers

A

act as the rate controllers except ensure that the setpoint and control point are the same

52
Q

Describe modulating combustion control as it applies to a steam boiler

A

occurs when a burner remains lit at all times but the flame size is increased or reduced by controlling the fuel and airflow to the burner according to steam pressure.

53
Q

Why the low level fuel cut-off on a hot water boiler cannot be tested in the same manner as a steam boiler

A

Because the boiler is completely filled with water along with the piping systems, it is difficult to lower the water level below the operation level for the low water cut-off device. If the drain valve is opened, the water will not drain out because the upper connection is also filled with water

54
Q

The CRT is the visual display or monitor used by a computer system to output visual information to the operator.

A

Cathode Ray tube

55
Q

A modulator-Demodulator that converts digital signals generated by a computer to analog signals for transmission over telephone lines, and then back to digital when received by the receiving computer

A

Modem

56
Q

Transfer input information to the computer in sequence with the correct timing, to be read into the computers memory and for processing

A

Input Multiplexer

57
Q

Bit

A

one digital piece of information represented by a 1 or a 0 with no other possible value

58
Q

Byte

A

Eight bits

59
Q

Read Only Memory which is burned into a chip and cannot be changed, and is not erased when the power is turned off.

A

ROM

60
Q

What are the 3 levels of computer languages

A

Machine language - consists of ones and zeros at the memory chip level. Used by manufacturers to program microcomputers.
Assembler language - a set of standard commands which the computer can interpret and convert to machine language.
High Level language - English like commands which can be used by the programmer to program the computer to perform any desired function within its capacity.

Power Engineering (7 decks)

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