Done by : 1-Amr Ghaith 2-Abdallah Hassouneh Universal shunt Done by : 1-Amr Ghaith 2-Abdallah Hassouneh

Universal Shunt Also known as Ayrton Shunt Ayrton shunt eliminates the possibility of having the meter in the circuit without a shunt used to increase the range of a galvanometer Ayrton shunt used with an ammeter consists of several series connected resistors all connected in parallel with PMMC instrument range change is effected by switch between resistor junction

The selector switch S ,selects the appropriate shunt required to change the range of the meter When the position of the switch is “1”then R1 is in parallel with the series combination of R2,R3 and Rm When the position of the switch is “2” then R1 and R2 are in parallel with R3 and Rm shunt

Note: -The larger the current, the value of the shunt resistance may become very small. -When using an ammeter you have to be aware of the following: 1. Observe the correct polarity. reversed polarity causes the movement to deflect against the mechanical stop (which cause some damage to the movement). 2. Never connect the ammeter across the element to be measured.

Here, due to the low resistance of the ammeter, this would draw a damaging high current and destroy the movement. Therefore, an ammeter must always be connected in series with the element to be measured. 3. When use a multi range ammeter first use the high current range, then decrease as required.

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

Rs=R1+R2+R3+R4=(Im)(Rm)/Is Rs=(0.05)(100)/( 0.95)= 5.26 Ω 1-Ampere Is= I - Im = 1- 0.05= 0.95 mA Rs=R1+R2+R3+R4=(Im)(Rm)/Is Rs=(0.05)(100)/( 0.95)= 5.26 Ω R1+R2+R3+R4= 5.26 Ω 1mA _ D’Arsonval Movement + 10mA 50mA 100mA

Rs=(R1+R2+R3)=(Rm+R4)(Im)/(Is) R1+R2 +R3 – 0.005R4=0.5 10-milliAmpere Is=10- 0.05= 9.95mA Rs=(R1+R2+R3)=(Rm+R4)(Im)/(Is) R1+R2 +R3 – 0.005R4=0.5 50-milliAmpere Is=50- .05= 49.95mA Rs=R1+R2=(Rm+R3+R4)(Im)/(Is) R1+R2- 0.001R3 -0.001=0.1 1mA _ D’Arsonval Movement + 10mA 50mA 100mA

100 milliAmpere Is=100- .05= 99.95mA Rs=R1=(Im)(Rm+R2+R3+R4)/(Is) R1- 0.0005R2-0.0005R3-.005R4=.05 1mA _ D’Arsonval Movement + 10mA 50mA 100mA

Ra=0.049 Rb= -0.04 Rc= -0.005 Note: if we design the circuit in the example as shown in the figure, we will observe the following results: