Universal shuntUniversal shunt

Done by :Done by :

1-Amr Ghaith 1-Amr Ghaith

2-Abdallah Hassouneh2-Abdallah Hassouneh

Universal ShuntUniversal Shunt

Also known as Ayrton ShuntAlso known as Ayrton Shunt Ayrton shunt eliminates the possibility of having the Ayrton shunt eliminates the possibility of having the

meter in the circuit without a shuntmeter in the circuit without a shunt used to increase the range of a galvanometer used to increase the range of a galvanometer Ayrton shunt used with an ammeter consists of several Ayrton shunt used with an ammeter consists of several

series connected resistors all connected in parallel with series connected resistors all connected in parallel with PMMC instrumentPMMC instrument

range change is effected by switch between resistor range change is effected by switch between resistor junctionjunction

The selector switch S ,selects The selector switch S ,selects the appropriate shunt the appropriate shunt required to change the range required to change the range of the meterof the meter

When the position of the When the position of the switch is “1”then R1 is in switch is “1”then R1 is in parallel with the series parallel with the series combination of R2,R3 and Rmcombination of R2,R3 and Rm

When the position of the When the position of the switch is “2” then R1 and R2 switch is “2” then R1 and R2 are in parallel with R3 and Rm are in parallel with R3 and Rm

Note:Note:-The larger the current, the value of the shunt -The larger the current, the value of the shunt resistance may become very small.resistance may become very small.

-When using an ammeter you have to be aware of the -When using an ammeter you have to be aware of the following:following:11. . Observe the correct polarity.Observe the correct polarity.

reversed polarity causes the movement to reversed polarity causes the movement to deflect against the mechanical stop (which deflect against the mechanical stop (which cause cause some damage to the movement).some damage to the movement).

2. Never connect the ammeter across the element to 2. Never connect the ammeter across the element to

be measured.be measured.

Here, due to the low resistance of the Here, due to the low resistance of the ammeter, this would draw a damaging high ammeter, this would draw a damaging high current and destroy the movement.current and destroy the movement.

Therefore, an ammeter must always be Therefore, an ammeter must always be connected in series with the element to be connected in series with the element to be measured.measured.

3. When use a multi range ammeter first 3. When use a multi range ammeter first use the high current range, then decrease use the high current range, then decrease as required.as required.

Design an Ayrton shunt to provide an ammeter Design an Ayrton shunt to provide an ammeter with a current range of 0-1 mA, 10 mA, 50 mA with a current range of 0-1 mA, 10 mA, 50 mA and 100 mA. A D’ Arsonval movement with an and 100 mA. A D’ Arsonval movement with an internal resistance of 100internal resistance of 100ΩΩ and full scale and full scale current of 50 uA is used.current of 50 uA is used.

1mA

R2

R1

R3

R4

_D’Arsonval Movement

+

+

_

10mA

50mA

100mA

1-Ampere1-Ampere

Is= I - Im = 1- 0.05= 0.95 mAIs= I - Im = 1- 0.05= 0.95 mA

Rs=R1+R2+R3+R4=(Im)(Rm)/IsRs=R1+R2+R3+R4=(Im)(Rm)/Is

Rs=(0.05)(100)/( 0.95)= 5.26 Rs=(0.05)(100)/( 0.95)= 5.26 ΩΩ

R1+R2+R3+R4= R1+R2+R3+R4= 5.26 5.26 ΩΩ

1mA

R2

R1

R3

R4

_D’Arsonval Movement

+

+

_

10mA

50mA

100mA

10-milliAmpere10-milliAmpere Is=10- 0.05= 9.95mAIs=10- 0.05= 9.95mA Rs=(R1+R2+R3)=(Rm+R4)(Im)/(Is)Rs=(R1+R2+R3)=(Rm+R4)(Im)/(Is) R1+R2 +R3 – 0.005R4=0.5R1+R2 +R3 – 0.005R4=0.5

50-milliAmpere50-milliAmpere Is=50- .05= 49.95mAIs=50- .05= 49.95mA Rs=R1+R2=(Rm+R3+R4)(Im)/(Is)Rs=R1+R2=(Rm+R3+R4)(Im)/(Is) R1+R2- 0.001R3 -0.001=0.1 R1+R2- 0.001R3 -0.001=0.1

1mA

R2

R1

R3

R4

_D’Arsonval Movement

+

+

_

10mA50mA

100mA

100 milliAmpere 100 milliAmpere Is=100- .05= 99.95mAIs=100- .05= 99.95mA

Rs=R1=(Im)(Rm+R2+R3+R4)/(Is)Rs=R1=(Im)(Rm+R2+R3+R4)/(Is)

R1- 0.0005R2-0.0005R3-.005R4=.05R1- 0.0005R2-0.0005R3-.005R4=.051mA

R2

R1

R3

R4

_D’Arsonval Movement

+

+

_

10mA

50mA

100mA

Ra=0.049Ra=0.049 Rb= -0.04Rb= -0.04 Rc= -0.005 Rc= -0.005

Note: if we design the circuit in the example as shown in the figure, we will observe the following results: