Self tests

Question 1

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

Answer 1

A transformer

Question 2

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

Answer 2

iron core, transformer, coil, meter movement

Question 3

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

Answer 3

keep it clean for accuracy

Question 4

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

Answer 4

Separate insert required for each range

Question 5

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?

Answer 5

8.8a (2.2x4) multiply no. of wraps

Question 6

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

Answer 6

do not need to de-energize/disconnect the load

Question 7

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

Answer 7

Net flux is zero due to the cancellation effect

Question 8

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

Answer 8

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

Question 9

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

Answer 9

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

Question 10

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

Answer 10

In parallel

Question 11

A shunt is a device that has a very _________ resistance

Answer 11

high

Question 12

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

Answer 12

To ensure small resistance change with temp. change

Question 13

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

Answer 13

5 micro amps

Question 14

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

Answer 14

So that the meter does not change normal operation

Question 15

What is the advantage of a multi range ammeter?

Answer 15

Convenience, takes more readings than one with a single meter

Question 16

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

Answer 16

counterclockwise; bent

Question 17

Name two types of ohmmeters?

Answer 17

Shunt ohmmeter

Series ohmmeter

Question 18

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

Answer 18

left

Question 19

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

Answer 19

left

Question 20

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

Answer 20

Shunt ohmmeter

Question 21

What is the disadvantage of the shunt ohmmeter?

Answer 21

cell discharges every time it turns on which drains its battery

Question 22

What type of ohmmeter is used in the multimeter?

Answer 22

series ohmmeter

Question 23

What is the function of the rheostat in the ohmmeter?

Answer 23

to compensate for low battery

Question 24

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

Answer 24

It keeps current at a safe maximum

Question 25

Are the scales of ohmmeters linear or non-linear?

Answer 25

non-linear

Question 26

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

Answer 26

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

Question 27

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

Answer 27

Yes

Question 28

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

Answer 28

higher ranges

Question 29

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

Answer 29

An energized circuit

Question 30

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

Answer 30

It will damage the meter

Question 31

Give two fundamental uses of the ohmmeter

Answer 31

Testing continuity | Finding resistance of loads

Question 32

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

Answer 32

1ohm

Question 33

What does an infinity reading on the ohmmeter indicate?

Answer 33

an open

Question 34

what does a zero reading on the ohmmeter indicate?

Answer 34

A short

Question 35

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

Answer 35

resistance | correct

Question 36

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

Answer 36

infinity

Question 37

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

Answer 37

Zero

Question 38

A megger is mainly used for testing _________ resistance

Answer 38

high resistance

Question 39

Why is an ohmmeter unsuitable for measuring insulation resistance?

Answer 39

The output voltage is too low

Question 40

What is the typical megger output voltages?

Answer 40

250, 500, 1000v DC

Question 41

Function of the clutch in a hand-cranked megger?

Answer 41

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

Question 42

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

Answer 42

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

Question 43

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

Answer 43

broken leads

Question 44

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

Answer 44

meter changes from measuring a load to a supply

Question 45

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?

Answer 45

battery is too weak

Question 46

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

Answer 46

discharge capacitors before testing the circuit

Question 47

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

Answer 47

The reading may be wrong due to parallel circuits

Question 48

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

Answer 48

There is a shock hazard or an error in the reading

Question 49

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

Answer 49

Separate the leads

Question 50

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

Answer 50

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

Question 51

State three precautions to be observed when working with the megger

Answer 51

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

Question 52

The watt-hour meter measures units of?

Answer 52

energy

Question 53

Energy is the product of what two quantities?

Answer 53

power and time

Question 54

Where is the energy meter in a house typically located?

Answer 54

on the side of house, face pointed out

Question 55

Identify 5 major components of the energy meter?

Answer 55

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

Question 56

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

Answer 56

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

Question 57

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

Answer 57

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

Question 58

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

Answer 58

varying position of damping magnet

Question 59

At what height must the energy meter be located?

Answer 59

1.5-1.8meters

Question 60

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

Answer 60

neutral

Question 61

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

Answer 61

to prevent energy theft