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Motor Conrols Final Review > Final Exam > Flashcards

Final Exam Flashcards

1
Q

How is Bimetallic strip made?

A

By bonding 2 dissimilar metals together

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2
Q

Why should electrical contacts never be permitted to open or close slowly

A

Produces poor contact pressure and causes contacts to burn

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3
Q

Two factors that determine the amount of voltage produced by a thermocouple?

A

1) the type of materials used
2) the temperature difference of the two junctions.

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4
Q

What do the letters RTD stand for?

A

Resistance temperature device

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5
Q

Type of wire used for RTD

A

Platinum

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6
Q

What material is a thermistor made of?

A

Semi conductor material

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7
Q

How can a silicon diode be made to measure temperature?

A

A constant current is passed through

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8
Q

What type of chemical is used to cause a pressure change in a bellows type thermostat?

A

Refrigerant

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9
Q

What two factors determine the polarity of the output voltage produced by a hall generator ?

A

1) the direction of current flow through semi conductor material

2) the polarity of magnetic fields

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10
Q

What two factors determine the amount of voltage produced by a hall generator?

A

1) the amount of current flow
2) the strength of magnetic field

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11
Q

What is a reluctor.

A

Is a ferrous metal disk used to shunt a magnetic field

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12
Q

Proximity detectors are basically ______?

A

Metal detectors

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13
Q

What type of electric circuit is used to increase the sensitivity of the proximity detector

A

Tank circuit

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14
Q

List 3 major categories of photodetectors

A

A) photovoltaic
B) photoemissive
C) photoconductive

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15
Q

Which category does the solar cell belong

A

Photovoltaic

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16
Q

Which category do phototransistors and photodiodes belong?

A

Photomissive

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17
Q

The term cad cell is a common name for what device ?

A

Cadmium solfide cell

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18
Q

What is the function of the transmitter in a photodetector unit ?

A

The light section

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19
Q

What is the advantage of a photodetector that uses a reflector to operate?

A

Needing electrical connection at only one piece of equipment

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20
Q

How much voltage is produced by a silicon solar cell ?

A

.5V

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21
Q

What is the operating voltage of most magnetic control systems?

A

120v

22
Q

How many primary windings do control transformers have?

A

2

23
Q

How are the primary windings connected when the control transformer is operated on 240V

A

Parallel

24
Q

How are the primary windings connected when the transformer is 480V

A

Series

25
Q

Why are two of the primary leads crossed on a control transformer

A

To make connection to primary easier

26
Q

Two basic classifications of timers

A

On delay
Off delay

27
Q

Explain the operation of an on delay relay?

A

When power is connected the contacts delay changing position

28
Q

Explain the operation of a off delay relay

A

When voltage is applied the contacts immediately from open to closed

29
Q

What are instantaneous contacts

A

Change their position immediately when energized, and immediately back when de energized

30
Q

How are pneumatic timers adjusted ?

A

Needle valve

31
Q

Name two methods used by electronic timers to obtain their time base

A

RC time constant
Crystal controlled clock

32
Q

What is meant by the statement “solenoid valves are digital device ?

A

Completely ON or completely OFF

33
Q

Why is it important the the inlet and outlet ports on a two way valve not be reversed?

A

Pressure of the inlet liquid and gas is used to maintain a seal

34
Q

What type of valve is generally used to supply air pressure to a double acting cylinder ?

A

Four way valves

35
Q

What two sections are generally used to operate motor operated valves ?

A

Local and remote

36
Q

What type of switch is used to ensure motor operated valve is tightly seated

A

Special limit switch

37
Q

Name three methods of braking a motor ?

A

Mechanical, dynamic, plugging

38
Q

How is braking force of drum brakes controlled ?

A

Break shoes

39
Q

Why are mechanical brakes used on cranes?

A

Because they can hold suspended loads

40
Q

What is a advantage of dynamic over mechanical brakes

A

No brake shoes to wear out

41
Q

What is a disadvantage of dynamic over mechanical

A

Can’t hold suspended loads

42
Q

The amount of counter torque developed by a direct current generator is proportional to what?

A

To armature current

43
Q

When using dynamic braking for a direct current motor, how is the braking time controlled ?

A

Adjusting resistance valve

44
Q

Name three factors that determine the amount of induced voltage

A

Strength of magnetic field
Speed of cutting action
Length of conductor

45
Q

How is a plugging stop accomplished ?

A

By disconnecting motor from power and momentarily reversing rotation

46
Q

What device is generally used to accurately stop a motor when a plugging stop is used ?

A

Zero speed switch

47
Q

What is the most common device used to disconnect the start winding of RS single phase motor

A

Centrifugal switch

48
Q

What electronic component is used in the construction of a solid state starting relay ?

A

Thermistor

49
Q

What percentage does a centrifugal switch disconnect

A

75%

50
Q

Why is it detrimental to disconnect the auto transformer before motor reaches run stage

A

Conserve energy

Motor Conrols Final Review (2 decks)

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