L3 Flashcards
including multi-meter’s current ranges have a certain resistance with particular
current and voltage requirement at full scale detection.
Ammeter
Multi-Meters inherently measure voltage, and pass a current to be measured through a shunt resistance, measuring the voltage developed across it.
Ammeter
The voltage drop is known as the “_____ _____,” specified in volts per ampere.
Burden voltage
It is an error/effect when the ammeter is inserted in the circuit of interest.
Burden voltage
can be significant in very low-voltage and low current circuit areas.
Burden voltage
Analog or deflection types are un-buffered, and draw current from the circuit
under test to deflect the meter pointer.
Voltmeter
The impedance of the meter varies depending on the basic sensitivity of the meter movement and the range which is selected.
Voltmeter
may not change in different ranges but this becomes significant when lower current range is selected.
Voltage drop
becomes additional load to the circuit being measured.
Voltmeter
The history of the basic meter movement used in direct current measurement can be trace back to
Hans Oersted’s discovery in 1820
What did Hans Oersted discovered in 1820
The relationship of Current and magnestism
Who discovered the relationship between current and magnetism
Hans Oersted
When did the relationship between current and magnetism discovered
1820
How many years did various types of devises that made used of the Oersted’s discovery were developed?
The next half of a century
one of the instruments for measuring electrical current par excellence.
Galvonometer
This device is used on electrical circuits to know and measure the intensity and direction of electrical current.
Galvonometer
Who discovered galvonometer
Luigi Galvani
When did Jacques D’Arsonval patented a moving coil galvanometer?
1881
What did Jacques D’Arsonval do in 1881
patented a moving coil galvanometer
Who patented a moving coil galvonometer in 1881?
Jacques D’Arsonval
is generally used for direct current measurement application.
D’Arsonval Meter Movement
What are other meter movement developed ?
Electrodynamometer movement and the Iron Vane meter movement.
What is the general application of iron vane meter movement and electrodynamometer
Alternating current measurement
AC measurement
Its general application is to measure ac.
Iron vane meter movement & electrodynamometer
The basic moving coil system is known as
D’Arsonval meter movement/ PMMC-Permanent Magnet Moving Coil Meter Movement
is generally set in a jewel and pivot suspension system to reduce friction.
Moving coil mechanism
Another method that provides a more sensitive but more expensive meter movement
Taut Band suspension system
a typical full scale current for a Jewel and Pivot suspension system is
5 micro A
a full scale current for Taut Band suspension system is ?
entirely practical
2 micro A
The typical commercial D’Arsonval Meter Movement operates on the principle of
DC motor
is a current responding device.
D’Arsonval meter movement
Current through coil causes it to behave as an _________ with its north and south poles.
Electromagnet
is the most fundamental meter movement used today
Electrodynamometer movement
is a current sensitive devise.
D’Arsonval meter movement & Electrodynamometer
That is the pointer deflects ______ because of the current flow through the moving coil.
Upscale
may be used to measure direct current or alternating current or voltage or single phase power in wattmeter.
Single coil meter movement
may be used in Polly-phase wattmeter and the crossed coil meter movement may be used as power factor meter or as frequency meter.
Double coil meter movement
electrodynamometer movement’s most important applications are as
volt meter and ammeter standard and transfer instrument.
Because of the inherent accuracy it is used as standard instrument for the calibration of other instruments.
Electrodynamometer
is applied to an instrument that may be calibrated with DC source then used without modification to measure AC.
Transfer instrument
This gave us direct means of equating AC and DC measurement of voltage and current with frequency limit of
0 - 125 Hz
consist of a fixed coil divided into two equal halves separated by a movable coil
single coil Electro dynamometer Movement
is capable of handling much more current than a D’Arsonval Meter Movement could handle without a shunt.
Electrodynamometer movement
the most extensive application of the electrodynamometer movement is in
Wattmeter
may be used for AC and DC power
Wattmeter
is consisting of a fixed coil of many turns and two iron vanes placed inside the fixed coil.
Iron Vane Meter Movement
It is widely used in industry for application in which ruggedness is more important than a high degree of accuracy.
Iron vane meter movement
The same square law meter scale used in
Electrodynamometer Movement is used in Iron Vane Meter Movement.
The moving vane instruments are rarely used for measuring direct current except for very inexpensive indicators such as charge and discharge indicators on automobiles.
Iron vane meter movement
are used extensively in industry for measuring alternating current, when 5% to 10% error is acceptable
Iron vane meter movement
It can be used for current and voltage measurements but it is very sensitive to frequency change.
Iron vane meter movement
This meter movement is sensitive to frequency primarily because magnetization of the iron vane is nonlinear and because of losses incurred by eddy current and hysteresis.
Iron vane meter movement
can change depending on the current range selected, since different ranges usually use different values of shunt resistance.
Percent of error/effect
To check for its effect on accuracy and on external circuit operation the meter can be switched to different ranges; the current reading should be the same and circuit operation should not be affected if
Burden voltage is not a problem
If this voltage is significant it can be reduced (also reducing the inherent accuracy and precision of the measurement) by
Using higher current ranges
To measure voltage, connect the voltmeter in parallel with the
Load and source of interest
( volt meter )This voltage drop is known as
Loading error/ effect
The moving coil mechanism is generally set in a
Jewel and pivot suspension system
is a horseshoe shaped permanent magnet with soft iron pole pieces attached to its north and south poles.
D’Arsonval meter movement
Because of the inherent accuracy it is used as standard instrument for the calibration of other instruments.
Electrodynamometer
Current from the circuit being measured passes through all the coils causing a _______ around the fixed coil.
Magnetic field
Since it has higher current handling capabilities due to its design it became less sensitive
Electrodynamometer
The electrodynamometer sensitivity is approximately about
20 to 100/V.
The electrodynamometer sensitivity is approximately about
20 to 100/V.
