Question
Download Solution PDFLet the resistance of a permanent magnet moving coil instrument be R Ω. What is the shunt resister required to measure a maximum current which is 5 times the full scale deflection current of the instrument?
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFFormula:
In a PMMC instrument
\({R_{sh}} = \frac{{{R_m}}}{{M - 1}}\)
\({R_m} = \frac{{{V_m}}}{{{I_m}}}\)
M = Multiplying factor = (Present FSD) / (Previous FSD)
Where,
Rsh = Shunt resistance
Rm = Meter resistance
Vm = Potential difference across meter
Im = Meter current
Calculation:
Given-
Rm = R Ω
Let the previous FSD current of PMMC is I, then present FSD current of PMMC is 5I
∴ \(M = \frac{{5I}}{I} = 5\)
\({R_{sh}} = \frac{R}{{5 - 1}} = \frac{R}{4}\)
Rsh = 0.25 R Ω
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