# How does an Ampmeter Work?

EPhantom
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How does an Amp-meter work?
How does and amp-meter work? It's suppose to have relatively no resistance, and can't change the circuits phase, so I can't figure it out… any one know of a simple circuit to explain how they work?
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4 years ago Report Abuse

protoham
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A DC amp-meter uses the equation V=IR to to make its measurement. This is simply done by placing a shunt (.001 to .1 ohm) resistor in line with the circuit and measuring a voltage across the shunt. The voltage is calibrated to through the equation to equate to Amps.

An AC amp-meter can be done in a couple of different ways:

1. Direct – In a similar manner as the above, but the voltage will go both positive and negative so a bridge diode is used to flop the negative voltage to a positive state then averaged with a capacitor. Then this is calibrated to a typical power factor. Keep in mind that current always lags voltage, so this makes AC theory more difficult to understand. Also the AC amps is expressed in RMS (root mean squared) values.

2. In direct – Because it is AC it will emit a electromagnetic field so a coil around the wire will pick up this field then run it through a shunt and measure it similar to 1.
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Paschal H
THis is a good question. If you are talking about on old style analog meter, it does have a small resistance and a small inductance. It is important to know this so you can understand how it might affect your circuit. The meters should have printed on them what this resistance and inductance is.

I believe the digital meters just use a small resistance and measure the voltage across this. These meters list this information on their spec sheets.
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dear
Dear pa,
Thank you, am also fine like you then your not mention amp-meter you need to know its working i.e.may analog or digital any way in analog there is a moving coil is there that respond in accord the produced magnetic flux when current passes through that path because this meter is connected in series with load.
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Warren W- a Mormon engineer
All DC amp meters work the same way. The current passes through a very small-value resistor creating a voltage drop. The voltage either drives a magnetic vane for a needle indicator, or provides a reference voltage for an electronic readout.

An AC amp meter also works this way, or it has a magnetic pickup coil to couple some of the alternating voltage to do one of the above.
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dmb06851
There is a type of ammeter (your "Amp-meter") which has not so far been mentioned.

It is the moving iron type.

The current which it is desired to be measured is passed through a coil.

The magnetic field produced buy that current attracts a piece of iron which is mounted at one end of a pivoted needle. The scale over which the needle moves is calibrated in current.

This type works on both d.c. and a.c.
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andrew b
Have a look at this reference:
http://tinyurl.com/48q8sr
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4 years ago

it is important to recognise the tautology here. Electricity and magnetism are utilised in the metric. They cannot be separated. Thus to assume that a current can be measured by an ampmetre is a mistake. The So called Electric voltage is measured , and this is taken as a measure of charge difference. The induction across the resistor is then made out to be different from the induction across a capacitor, and the magnetic field effects are totally ignored unless impedance is noted.

The assumption hat this subject can be dissected into electricity and magnetism is false, it was recognised as false during he 1920s but yet it is still taught in this way with the word electromagnetism thrown in to distract the uninitiated from this fundamental miseducation!

If Ed Leedskalnin stands for anything, he stand for the correct approach to education with regard to fundamental force systems in our world. It is not that we do not have these fundamental paradigms, it is that we do not use them, preferring half truths instead.

How does a voltmeter work to measure voltage?
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2 years ago Report Abuse

Larry
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Measuring Voltage
Measuring the voltage between two points of an electrical current can be done with an instrument called a voltmeter. One type of voltmeter is a direct-current voltmeter. When taking a voltage reading the instrument is placed across the portion of the circuit that is to be measured.
Direct-Current Voltmeter
The direct-current voltmeter has a horseshoe shaped magnet, with a semicircular piece of soft iron attached to each end of the magnet. The iron is also magnetized. The iron ends of the magnet serve to direct the magnetic field in the direction of a small iron cylinder that is positioned between the ends (or poles) of the magnet. Taking advantage of the soft iron's characteristic to become highly magnetized, the iron cylinder focuses the magnetic field.
The Electrical Current
Surrounding the cylinder is a rectangular frame with a copper wire coil, with the ends of the wire attached to small spiral springs. Attached to the coil is a needle. The coil carries the electrical current, causing the needle to move. When the needle moves, it points to a reading on a dial which represents voltage.
The needle will point to zero on the dial when the voltmeter is not in use. When a current moves through the coil, the magnetic field creates a force on the coil, resulting in needle movement. The force, caused by the electrical current running through the coil and the magnetic field of the magnet, causes the coil to turn. The springs attached to the ends of the coil oppose the coil's motion, which serves to adjust the position of the needle to indicate the correct voltage.

Read more: How Does a Voltmeter Work? | eHow.com http://www.ehow.com/how-does_4596999_a-v
Source(s):
http://www.ehow.com/how-does_4596999_a-v
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dwarf
Volt meter is basically microampere meter . The smaller the current of the meter the better the accuracy. The current required to indicate full scale reading of the ammeter is called sensitivity.Usually measure in micro ampere .
In order to make ammeter to measure voltage just add a series resistor.

Let say ammeter sensitivitity is 1 uA and internal resistance of coil is 100 ohms.

To measure 10 V to be full scale resistor value should be

1uA= 10/(100+R)
1 x 10^-6 x (100+R) = 10
100+ R = 10 x 10^6
R = 10×10^6 -1 x 100
R= 100000×10^2 – 1 x 10^2
R = 99999 ohms or 99.999 kohms.

Seneitivity of the volt meter is defined as kohms /volt
In above example meter sensitivity is 9.9 khoms /volt.(99.999kohms/10volts)

Most analog multi meter has sensitivity of 20kohms/volt for DC voltage measurement.
We need high sensitivity ( high kohms/volt ) meter in order not to add additional load to the circuit.
Ideal volt meter should have infinity internal resistance.
Ideal ammeter should have zero internal resistance.

Sorry for my poor english.
I hope I did not confuse you.
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