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Meters > Self tests > Flashcards

Self tests Flashcards

1
Q

The AC clamp-on-ammeter operates on the principle of which common device?

A

A transformer

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2
Q

Identify the fundamental parts of an AC clamp-on-ammeter?

A

iron core, transformer, coil, meter movement

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3
Q

What care should be taken with respect to the jaws of the clamp-on-ammeter?

A

keep it clean for accuracy

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4
Q

Name one disadvantage of the old DC clamp on ammeter, commonly called the tong-tester?

A

Separate insert required for each range

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5
Q

The current in a conductor is 2.2A. If four turns of this conductor are looped through the core of a clamp-on-ammeter, what current on the scale should the pointer indicate?

A

8.8a (2.2x4) multiply no. of wraps

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6
Q

What is the outstanding advantage of clamp-on-ammeters compared to their in-line counterparts?

A

do not need to de-energize/disconnect the load

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7
Q

When the hot and return conductors are pooped through the core of the clip-on ammeter, why does it normally read zero?

A

Net flux is zero due to the cancellation effect

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8
Q

Most AC clamp-on ammeters have a locking device that allows for locking the pointer. What is the reason for this?

A

To lock in the reading when the scale is not visible, also protects the movement when it’s not in use

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9
Q

Clamp-on ammeters sometimes also incorporate voltmeters. Briefly explain why this is possible?

A

Clamp-on ammeters use D’Arsonval movement. This movement is also used to measure voltage

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10
Q

How is a shunt connected in relation to the coil of the galvanometer?

A

In parallel

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11
Q

A shunt is a device that has a very _________ resistance

A

high

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12
Q

Why are shunt resistors made from materials having a low temperature coefficient?

A

To ensure small resistance change with temp. change

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13
Q

Full-scale deflection current for the coil in the D’Arsonval mater movement could be as low as?

A

5 micro amps

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14
Q

Why is it desirable to have the resistance of an ammeter as low as possible?

A

So that the meter does not change normal operation

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15
Q

What is the advantage of a multi range ammeter?

A

Convenience, takes more readings than one with a single meter

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16
Q

If the polarity of the leads on a D’Arsonval meter are reversed, the pointer will move _____?

A

counterclockwise; bent

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17
Q

Name two types of ohmmeters?

A

Shunt ohmmeter

Series ohmmeter

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18
Q

In the series ohmmeter, the high resistance values are on the ________ side of the scale?

A

left

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19
Q

In the shunt ohmmeter, the low resistance values are on the _________ side of the scale?

A

left

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20
Q

Which type of ohmmeter is more suitable for measuring low resistor values?

A

Shunt ohmmeter

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21
Q

What is the disadvantage of the shunt ohmmeter?

A

cell discharges every time it turns on which drains its battery

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22
Q

What type of ohmmeter is used in the multimeter?

A

series ohmmeter

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23
Q

What is the function of the rheostat in the ohmmeter?

A

to compensate for low battery

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24
Q

What is the purpose of the fixed resistor in the ohmmeter?

A

It keeps current at a safe maximum

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25
Q

Are the scales of ohmmeters linear or non-linear?

A

non-linear

26
Q

State briefly two general methods that allow an ohmmeter to have several ranges

A

using more than one voltage, using a shunt-type operation

27
Q

When using a multi range ohmmeter, is it necessary to zero-adjust the meter for each range scale?

A

Yes

28
Q

Is the higher voltage battery used for the higher or lower ranges of resistance measurement

A

higher ranges

29
Q

To what type of circuit or device must an ohmmeter never be connected?

A

An energized circuit

30
Q

What is the reasoning for not connecting an ohmmeter to an energized circuit or source?

A

It will damage the meter

31
Q

Give two fundamental uses of the ohmmeter

A

Testing continuity

Finding resistance of loads

32
Q

What is the resistance value below which the ohmmeter is considered inaccurate for measuring?

A

1ohm

33
Q

What does an infinity reading on the ohmmeter indicate?

A

an open

34
Q

what does a zero reading on the ohmmeter indicate?

A

A short

35
Q

When testing for continuity, the primary concern is not the circuit _________ value, but to check that the circuit is _________

A

resistance

correct

36
Q

If the ohmmeter leads are separated in air, the pointer will read?

A

infinity

37
Q

If the leads of the ohmmeter are touching, the pointer will read?

A

Zero

38
Q

A megger is mainly used for testing _________ resistance

A

high resistance

39
Q

Why is an ohmmeter unsuitable for measuring insulation resistance?

A

The output voltage is too low

40
Q

What is the typical megger output voltages?

A

250, 500, 1000v DC

41
Q

Function of the clutch in a hand-cranked megger?

A

To slip if cranked too fast in order to not exceed rated values

42
Q

List 3 precautions to be observed before you connect the leads of an ohmmeter to a component.

A

De-energize the circuit
do not hold test lead ends
make sure it has been zeroed

43
Q

If, when the leads of an ohmmeter are joined, the pointer is still at infinity, what might be the reason?

A

broken leads

44
Q

Why does the polarity of the leads of a multimeter reverse when the meter is used to measure resistance?

A

meter changes from measuring a load to a supply

45
Q

If the zero-adjust on an ohmmeter fails to bring the pointer to zero when the leads are joined, what is most likely the cause?

A

battery is too weak

46
Q

What precaution should you take when measuring circuits that may have capacitors?

A

discharge capacitors before testing the circuit

47
Q

Why is it correct to always isolate at least one of the two ends of a component being tested with an ohmmeter?

A

The reading may be wrong due to parallel circuits

48
Q

Why should you avoid touching the bare leads of the ohmmeter when checking a component or circuit?

A

There is a shock hazard or an error in the reading

49
Q

In a shunt-type ohmmeter, what should you do to the leads while zeroing the meter?

A

Separate the leads

50
Q

What is the rule with regard to zeroing when using a multi range ohmmeter on different range settings?

A

meter must be zeroed when changing from one scale to the next

51
Q

State three precautions to be observed when working with the megger

A
  • do not connect to an energized circuit
  • do not use on low voltage circuits
  • be aware charges can be built up by a megger
52
Q

The watt-hour meter measures units of?

A

energy

53
Q

Energy is the product of what two quantities?

A

power and time

54
Q

Where is the energy meter in a house typically located?

A

on the side of house, face pointed out

55
Q

Identify 5 major components of the energy meter?

A

current coils, voltage coil, disk, dials, damping magnet

56
Q

What factors determine the speed of the rotating disk in a kilowatt-hour meter?

A

current in the current coils (load current) voltage across voltage coil (load voltage)

57
Q

What is the purpose of the damping magnets in the energy meter?

A

to create counter-torque on a disk to allow speed adjustments

58
Q

How can the speed of the aluminum disk be fine-tuned? (adjusted up or down)

A

varying position of damping magnet

59
Q

At what height must the energy meter be located?

A

1.5-1.8meters

60
Q

which of the three conductors going to the meter is not broken at the meter?

A

neutral

61
Q

why does the power supply company place a seal on the meter

A

to prevent energy theft

Meters (3 decks)

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