How is a Galvanometer Converted into an Ammeter Using a Shunt?

[Hardik Batra]

To make ammeter,
Resistance of proper small value is joined in parallel to the coil of galvanometer.This resistance is called a shunt.


For smaller resistance value,
We can not use the smallest resistance wire that is directly wound on coil of galvanometer so the resistance will become minimum.?

 

[davenn]

hi there Hardik

do you understand what the shunt resistance does ?
I suspect not

the coil resistance on its own may give a full scale reading of say 100mA
but what if you wanted to read 1A or 10A or 100A ?

so for example if you want to read 10A full scale, and the coil can only read 100mA full scale, then the shunt must pass the other 9.9 Amps (9900 mA)

Here's an excellent article on the use and calculating of shunt resistors ...
http://www.allaboutcircuits.com/vol_1/chpt_8/4.html

cheers
Dave

 

[Hardik Batra]

In (fig. a) we want to measure current passing through the resistance R in a circuit shown in fig.

I=V/R

In (fig. b) galvanometer is joined in series with resistance R, as shown in fig.

In such connection resistance G of the galvanometer is added in the circuit

and as the total resistance of the circuit is changed the value of current to be measured itself is changed

I = V/(R+G)

Thus the true value of current is not obtained.

this fact indicates that the resistance of current meter should be as small as possible.

So we can't use the low resistance wire that directly wound on coil so that you will get directly,

I = V/R.

 

[sophiecentaur]

To make ammeter,
Resistance of proper small value is joined in parallel to the coil of galvanometer.This resistance is called a shunt.For smaller resistance value,
We can not use the smallest resistance wire that is directly wound on coil of galvanometer so the resistance will become minimum.?

As with all Engineering, it's a matter of compromise, using the materials that are available.
The galvanometer needs to be sensitive enough to detect very small currents. The movement needs to be very light, so it responds quickly to a short pulse. That forces the use of thin wire which will burn out with higher currents. So you are stuck with a resistance that is not that low (you need sufficient turns on the armature to get a deflection).

For measuring higher values of current, the shunt dissipates most of the energy so the coil won't burn out.

 

[pmacias]

The use of a shunt to convert a galvanometer into an ammeter is a common practice in the field of electrical engineering. By adding a shunt in parallel to the galvanometer's coil, the overall resistance of the circuit is reduced, allowing for a larger current to flow through the ammeter. This is necessary because the coil of a galvanometer is typically designed to have a high resistance, which is suitable for measuring small currents. However, when measuring larger currents, the high resistance of the galvanometer would limit the amount of current that can flow through it and potentially damage the instrument. By using a shunt, we can effectively decrease the overall resistance of the circuit and allow for accurate measurement of larger currents. This is a practical and efficient way to transform a galvanometer into an ammeter.