A thermocouple circuit uses a chromel-anumel thermocouple which gives an emf of 33.3 V when measuring a temperature of $800^{o} C$ with reference temperature $0^{o} C$ . The resistance of the meter coil, $R_{m} i s 50 Ω$ and a current of 0.1 mA gives full scale deflection. The resistance of junctions and leads, $R_{c}, i s 12 Ω .$ Calculate resistance of the series resistance if a temperature of $800^{o} C$ is to give full scale deflection.

The resistance temperature co-efficient of coil is $0.00426 /^{o} C .$

100 Ω

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271 Ω

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171 Ω

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111 Ω

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Solution

The correct option is B $271 Ω$
$Emf (E) = i (R_{m} + R_{s} + R_{e})$

$33.3 \times 10^{- 3} = 0.1 \times 10^{- 3} (50 + R_{s} + 12)$

$or, series resistance (R_{s}) = 271 Ω$

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The correct option is B 271ΩEmf (E)=i(Rm+Rs+Re) 33.3×10−3=0.1×10−3(50+Rs+12) or, series resistance (Rs)=271Ω

The correct option is B $271 Ω$
$Emf (E) = i (R_{m} + R_{s} + R_{e})$

$33.3 \times 10^{- 3} = 0.1 \times 10^{- 3} (50 + R_{s} + 12)$

$or, series resistance (R_{s}) = 271 Ω$