Conversion of a Galvanometer to an Ammeter

In summary, the conversation discusses the concept of converting a galvanometer into an ammeter by connecting a shunt in parallel to the galvanometer. This allows for a more sensitive measurement of current, as the majority of the current flows through the shunt instead of the galvanometer. The conversation also touches on the idea of using a calibrated scale and adding a series resistance to convert the galvanometer into a voltmeter.
  • #1
zorro
1,384
0
I had this doubt for over 1 year! I thought of asking about it here.

In the conversion of a galvanometer to an ammeter by connecting a shunt in parallel to the galvanometer, maximum amount of current flows through the shunt because it has a very very low resistance. In other words, very less amount of current flows through the galvanometer branch. How does it measure the correct current flowing through the circuit?

If we connect a normal ammeter in series, all the current flows through it and hence it measure the correct current flowing.
 
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  • #2
An ammeter normally has a low resistance and is used in series so all the current flows through it. The lower you can make it's resistance the more sensitive it is - since less current is needed to show a reading.

But suppose you had an ammeter which went to full scale with only 10mA flowing through it and you wanted to measure a current of 10amps? You need to make it so only 1/1000 of the current goes through the meter - so you put a resistor of 1/1000 the resistance of the ammeter in series with it.
 
  • #3
NobodySpecial said:
The lower you can make it's resistance the more sensitive it is - since less current is needed to show a reading.

For an ammeter (converted) to show a reading of say 10mA, all this current should flow through the galvanometer branch. If only a small part of it say 0.01mA flows through it, then the galvanometer measures 0.01mA as the current flowing. How will it measure 10mA?
 
  • #4
Abdul Quadeer said:
For an ammeter (converted) to show a reading of say 10mA, all this current should flow through the galvanometer branch. If only a small part of it say 0.01mA flows through it, then the galvanometer measures 0.01mA as the current flowing. How will it measure 10mA?

That is why you have a calibrated scale behind the needle. The shunt resistor used determines which scale you read. So the same current through the galvo coil will represent a different current through the shunt.
 
  • #5
Integral said:
That is why you have a calibrated scale behind the needle. The shunt resistor used determines which scale you read. So the same current through the galvo coil will represent a different current through the shunt.

What happens if we make the shunt resistance very large compared to the galvanometer so that all the current flows through the galvanometer. Can't we calibrate the galvanometer this way?
 
  • #6
If you see a galvanometer, there is a rating. 20 μA/div. If the galvanometer has 30 divisions, it gives full scale deflection for 600 μA. You can measure the current up to 600 μA with the accuracy of 20 μA. If you want to increase the range of the ammeter from 0 to 10 A, constructed by the above galvanometer, you have to connect a low resistance shunt across the galvanometer such that when 10 A current is flowing in the circuit, only 600 μA flows through the galvanometer. Rest of the current flows through the shut to the main circuit.
 
  • #7
I suggest the best way to think of a galvanometer is as a very sensitive ammeter - a microammeter in fact.

The term galvanometer was introduced long before dedicated voltmeters, ammeters or modern convenient multimeters were introduced.

You can perform the same shunt ( or parallel) resistance trick with any ammeter to anhance its range.

Similarly you can convert it into a voltmeter by adding a series resistance.
 
  • #8
rl.bhat said:
If you see a galvanometer, there is a rating. 20 μA/div. If the galvanometer has 30 divisions, it gives full scale deflection for 600 μA. You can measure the current up to 600 μA with the accuracy of 20 μA. If you want to increase the range of the ammeter from 0 to 10 A, constructed by the above galvanometer, you have to connect a low resistance shunt across the galvanometer such that when 10 A current is flowing in the circuit, only 600 μA flows through the galvanometer. Rest of the current flows through the shut to the main circuit.

Thanks! I understood it with your example.
 

1. How does a galvanometer convert to an ammeter?

The conversion process involves adding a shunt resistor in parallel with the galvanometer, which allows a portion of the current to bypass the galvanometer and measure the larger current passing through the circuit. The shunt resistor must have a known resistance value and must be carefully selected to ensure that it does not significantly affect the overall resistance of the circuit.

2. What is the purpose of converting a galvanometer to an ammeter?

The purpose is to measure larger currents (typically in the range of milliamps to amps) that a galvanometer alone would not be able to measure accurately. This allows for more precise and versatile measurements in experiments and in various electrical circuits.

3. How does the conversion affect the accuracy of the galvanometer?

The conversion process does not affect the accuracy of the galvanometer itself, as the shunt resistor is carefully selected to have minimal impact on the overall resistance of the circuit. However, the accuracy of the ammeter may be affected if the shunt resistor is not of high enough quality or if there are any other errors in the circuit.

4. Can any galvanometer be converted to an ammeter?

No, not all galvanometers can be converted to ammeters. The galvanometer must have a sensitive coil and a low resistance to begin with in order for the conversion to be successful. Additionally, the galvanometer must have a suitable range of measurement for the desired ammeter.

5. Are there any precautions to take when converting a galvanometer to an ammeter?

Yes, there are several precautions to take when converting a galvanometer to an ammeter. These include selecting the proper shunt resistor, ensuring the galvanometer can handle the desired range of measurement, and making sure the circuit is properly calibrated. It is also important to be careful when handling and connecting the shunt resistor to avoid any damage to the galvanometer or other components.

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