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ELX > A3 LT4 > Flashcards

A3 LT4 Flashcards

1
Q

Where is the movable electric contact mounted?

A

On the armature

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2
Q

What happens when current flows through the coil?

A

Armature attracted to coil core

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3
Q

What is the basic meter movement used in most commercial analog meters?

A

D’Arsonval meter

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4
Q

What does current flow in the coil of an analog meter produce?

A

Clockwise torque

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5
Q

What is the basis for meters measuring AC and DC currents and voltages, as well as resistance?

A

D’Arsonval movement

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6
Q

Where is the stationary contact mounted?

A

On the same base as the coil core

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7
Q

What happens when the current stops flowing?

A

Spring causes armature to move away

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8
Q

What is the basic construction of the meter movement called?

A

D’Arsonval meter

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9
Q

What is the torque in the coil of an analog meter directly proportional to?

A

The amount of current flowing in the coil

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10
Q

What causes the pointer in an analog meter to oscillate?

A

Combined action of moving coil and restraining springs

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11
Q

What is the purpose of contacts?

A

Isolate the coil from the current.

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12
Q

What is the moving coil in an analog meter made of?

A

Fine copper wire

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13
Q

Why is the instrument movement in a D’Arsonval meter extremely delicate?

A

Can only handle milliamps or microamps

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14
Q

Why is damping necessary in an analog meter?

A

To suppress oscillation

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15
Q

What must be done to release the material attracted to the lifting magnet?

A

Open the switch to stop current flow

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16
Q

What does the current passing through the coils produce?

A

Magnetic field

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17
Q

What is the aluminum frame in an analog meter mounted on?

A

Shaft pivoted between two jewelled bearings

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18
Q

What is a relay?

A

Electromagnetic switch

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19
Q

How does the current flow in the system when the bell button is pressed?

A

Current starts to flow again

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20
Q

What happens as the cycle repeats itself with the bell system?

A

Armature repeatedly strikes the bell

21
Q

What are motors and generators commonly used for?

A

Produce mechanical energy from electrical energy

22
Q

How are field poles created in these machines?

A

Passing a current through coils wound around a magnetic core called the stator

23
Q

What enables the coil in an anoalog meter to move freely?

A

Jewelled bearings

24
Q

What happens when the current through an undamped analog meter is increased suddenly from 0 to some value A amps?

A

Pointer oscillates about the value A before coming to rest.

25
Q

What happens when current is passed through a coil?

A

Attracts a spring-loaded armature

26
Q

What causes the contacts to come together and close the switch?

A

Current flowing through the coil

27
Q

What controls the magnitude of the current through the field coils?

A

Field rheostat

28
Q

What is attached to the coil in an analog meter?

A

Pointer

29
Q

Why is it difficult to read the analog meter quickly and accurately?

A

Pointer oscillates with every fluctuation of current.

30
Q

How are magnetic relays used?

A

Small current controls large current

31
Q

Why is the flux density of the field varied in these machines?

A

To control speed, torque, and voltage

32
Q

How is the current conducted to and from the coil in an analog meter?

A

Spiral springs

33
Q

How does the deadbeat instrument behave?

A

pointer moves across smoothly without oscillation

34
Q

What is similar about the operation of a bell and a buzzer?

A

Same basic operation.

35
Q

What keeps the coil in the rest position when no current flows in an analog meter?

A

Spiral springs

36
Q

What happens when the armature moves toward the coils?

A

Strikes the bell

37
Q

How is current indicated in the coil of an analog meter?

A

By the attached pointer on a calibrated scale

38
Q

What is the function of the two springs in the coil of an analog meter?

A

They conduct current to the coil and restrain its movement

39
Q

What does the D’Arsonval movement require to measure AC values?

A

Built-in rectifier

40
Q

What happens to the core when a current is passed through the coil?

A

Becomes magnetized and poles are formed

41
Q

What happens when the current stops flowing in a core with low retentivity?

A

Field collapses and material is released

42
Q

What pulls the armature away from the coils?

A

Spring

43
Q

What two principles does the operation of an analog meter depend on?

A

Coil becoming an electromagnet; Like poles repel, unlike attract

44
Q

What does the D’Arsonval movement require to measure resistance?

A

Internal battery

45
Q

What is the difference between a buzzer and a bell in terms of the armature?

A

No bell to strike for the buzzer

46
Q

What do generators use to produce electrical energy from mechanical energy?

A

Magnetoelectric effect

47
Q

What are the magnetic poles required for generators and motors called?

A

Field poles

48
Q

When does the pointer stop moving in the coil in an analog meter?

A

When the torques balance each other out

49
Q

What is the maximum current the coils in a D’Arsonval meter movement can handle?

A

About 50 mA

ELX (55 decks)

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