Meters Flashcards
What device must be used with the D’Arsonval movement to enable the meter to read AC?
Rectifier
What is meant by “damping” a meter movement?
smoothing it out or oscillating
If you are using a multi-range meter and there is some doubt what the reading would be. What should you always do?
Read at the highest scale
What could happen if your leads are reversed when measuring DC?
It could damage the meter
What size of wire does a D’Arsonval movement have?
Very fine wires
What is the max current that the D’Arsonval movement can handle without damage?
50mA
What is it called when you get an incorrect reading because you are not looking at an analog meter straight on?
Parallax
What does a multimeter read?
AC DC volts
AC DC amps
Ohms
What is the purpose of a reset button in a multimeter?
To reset the internal circuit breaker
What must be used with the D’Arsonval movement in order to read voltage?
Large resistor
What is it called when a voltmeter changes the circuit that it is trying to read?
meter loading
Rule of thumb. How much bigger should the resistance in the meter be to the load it is measuring?
10 times
What should you check before connecting to a DC voltage source?
Polarity
Before using a meter or tester, you should check what first?
The scale
The common lead should always be what colour?
Black
A voltmeter is rated 10kohms/v and the range selector switch is on 50v. What is the resistance of the meter? (Rm)
500,000ohms
Meters are classified into 2 general groupings. What are they?
digital and analog
What is one commonly used type of meter movement called?
D’Arsonval
In what position should you store a meter if it does not have an off position?
highest AC volts setting
What is the resistor called that is in series with the meter movement coil in a voltmeter?
multiplier
Which meter would be more delicate? 1,000ohms/V or 10,000ohms/V
10,000
Does a voltmeter have high or low resistance?
high
Does an ammeter have high or low resistance?
low
How is the resistor connected in a voltmeter?
parallel
How is the resistor connected in an ammeter?
series
What tester has 2 insulated test leads, a neon bulb, and a bulb holder?
Neon voltage tester
Neon bulbs have high resistance and generally require at least _____ volts to initially switch on?
90 volts
What is a more common name for a solenoid and plunger tester?
A wiggy
What is the max amount of time that a solenoid and plunger should be connected to voltage sources?
20 seconds
If the solenoid and plunger tester is vibrating, what does this mean?
It is measuring A/C
When the electrode on the left side glows, the black test lead is?
negative
when the electrode on the right side glows, the red test lead is?
negative
What is the max amount of voltage that you can measure with a solenoid and plunger tester?
600v
Which tester is used to check branch circuit receptacles?
an outlet analyzer
In an ammeter, what is the resistor called to limit the current to the meter movement?
Shunt
Where is the resistor located in the circuit?
parallel
What must you do if you want to change the setting range on a multi-range ammeter?
turn it off
What type of switch makes a new electrical connection before the previous one is turned off?
Make before break switch
Which meter is more sensitive. 50microamps or 50milliamps?
50microamps
What type of ohmmeter is the most common?
Series ohmmeter
What is the fixed resistor for?
limiting current flow from exceeding ratings
What is the rheostat for?
to compensate for low battery
Which type of ohmmeter is used in a multimeter?
series
What is the main advantage of the shunt type ohmmeter?
measures low resistances
What is one disadvantage of the shunt ohmmeter?
the cell discharges when in use
How can you tell the difference between series and shunt ohmmeters?
0 is on the left for shunt
0 is on the right for series
Give two applications that we would use an ohmmeter for?
measuring resistance
continuity tests
What does a zero reading indicate?
short circuit
what does an infinity reading indicate?
an open
What is a megger used for?
measuring high resistances
What are normal voltages a megger can put out?
250,500,1000v DC
Most hand crank meggers have a clutch, what is it for?
Clutch will slip if voltage rating exceeds
List 4 precautions when using a megger
- do not exceed rated values
- high resistances only
- do not touch leads
- do not measure low voltage circuits
In an ammeter, at what current must we use an external resistor?
25amps or more
What would the external resistor of the ammeter be made out of?
copper
What precautions should you take when testing circuits that contain capacitors?
discharge the capacitor if it holds a charge
Why is an ohmmeter unsuitable for measuring insulation resistance?
the output voltage is too low
If the leads of an ohmmeter are touching the pointer will read?
zero
The AC clamp-on ammeter operates on the principle of which common device?
transformer
In the ammeter the shunt is connected in___________ to the galvanometer?
parallel
Why are larger shunts not placed within the case of the meter?
It would get too hot
What is meant by meter loading?
It changes the values of the circuit
Why do shunt resistors have low-temperature coefficient?
So they don’t change resistance when heated
Neon type testers are usually not used on circuits less than?
90volts
Sensitivity of Voltmeter?
50microamps to 50milliamps
Sensitivity of ammeter?
5microamps to 50milliamps
