Question:
A multirange current meter can be constructed by using a galvanometer circuit shown in the figure. We want a current meter that can measure 10 mA, 100 mA, and 1 A using a galvanometer of resistance 10Ω and that produces maximum deflection for a current of 1 mA. Find S1, S2, and S3 that have to be used.
Solution:
I1 is measured as = 10 mA = IGG = (I1 – IG)(S1 + S2 + S3)
I2 is measured as = 100 mA = IG(G+S1)=(I2-IG)(S2-S3)
I3 is measured as = 1 A = IG(G+S1+S2)=(I3-IG)(S3)
S1 = 1 Ω
S2 = 0.1 Ω
S3 = 0.01 Ω