Flashcards in Electricity 5 Of 7 Deck (34)
What are the four basic meters?
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.
The ___________ meter uses the heat produced by a wire to measure current.
The __________ of the magnetic field is proportional to the amount of ______________ flowing through the coil.
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?
Because it is very accurate and rugged, the _______________ is the most common meter used
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.
In the concentric-vane meter, the stationary vane is ______ to provide a nonuniform magnetic field between the two vanes.
What are the typical three shapes of pointers?
The ___________ meter movement is used most often because it is more sensitive and more accurate.
By using a _________ to convert ac to dc, moving-coil meters can be used in a-c applications.
To calibrate a d-c meter, an ___________ d-c current source is connected.
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.
What type of special resistor is used in amp meters?
Meters designed to measure currents above 30 amps generally use _________ shunts.
A rectifier changes a sine wave into a __________ d-c wave.
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.
A________ is used to select a particular shunt for the desired current range.
A current meter must always be connected in __________ with the power source and load.
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.
The closer a pointer is to __________________ the more accurate it is.