Electricity 5 Of 7 Flashcards
What are the four basic meters?
1-ammeter
2-voltmeter
3-ohmmeter
4-wattmeter
Can a current meter be calibrated in units other that amps?
Yes, in can be calibrated in voltage and resistance because all three are related to ohms law
When current flows through a wire, it produces what two effects?
1-it creates a magnetic field around the wire.
2- it generates heat
The _________ current meter makes use of the magnetic field around a current-carrying wire to measure current.
Electromagnetic
The ___________ meter uses the heat produced by a wire to measure current.
Thermal
The __________ of the magnetic field is proportional to the amount of ______________ flowing through the coil.
Strength
Current
What are the two types of electromagnetic current meters?
1) moving-coil type
2) moving-iron type
The first known moving-coil meter was called?
Galvanometer
Because it is very accurate and rugged, the _______________ is the most common meter used
Moving-coil movement
What are the three types of moving-iron meters?
1) radial vane
2) concentric-vane, and
3) plunger type
When current flows through a wire, the wire is heated_________ to the current flow.
Proportionally
In the concentric-vane meter, the stationary vane is ______ to provide a nonuniform magnetic field between the two vanes.
Tapered.
What are the typical three shapes of pointers?
Spade
Knife
Lance
The ___________ meter movement is used most often because it is more sensitive and more accurate.
Moving-coil
By using a _________ to convert ac to dc, moving-coil meters can be used in a-c applications.
Rectifier
To calibrate a d-c meter, an ___________ d-c current source is connected.
Accurate.
The d-c current source used to calibrate a d-c meter must be very accurate and?
Be variable and have a means to monitor the output current.
The accuracy of a meter is the percentage error at ____________ deflection.
Full-scale
What type of special resistor is used in amp meters?
A shunt.
Meters designed to measure currents above 30 amps generally use _________ shunts.
External
A rectifier changes a sine wave into a __________ d-c wave.
Pulsating
What are the two types of rectifiers?
Full wave and half wave
What is used in a full-wave rectifier to allow current to flow in the same direction during both alternations of a sine wave?
Bridge rectifier circuit
__________ rectifiers measure only one half the alternation of a sine wave.
Half-wave
A________ is used to select a particular shunt for the desired current range.
Range switch
A current meter must always be connected in __________ with the power source and load.
Series
Do you have to observe the polarity when connection a meter to ac?
No, because the polarity changes with each alternation
A clamp-on meter acts like a _________ because current through the conductor produces a magnetic field which induces current.
Transformer
The closer a pointer is to __________________ the more accurate it is.
Full-scale deflection
The voltage range of a meter can be extended by adding a _______ in series.
Multiplier resister
Whether measuring ac or dc voltage, connect the voltmeter in _________\ with the component.
Parallel
The ohms/volt rating for multi range voltmeter is the _________ for all ranges.
Same
How is the sensitivity of a voltmeter expressed?
By its ohms/volt rating.
Shunt ohm meters are connected in ________, and series type ohm meters are connected in __________.
Parallel
Series
