GATE 2021 IN – Question 63
The full bridge shown uses linear strain gauges with gauge factor 2. At 0 °C and zero strain, $R_1=R_2=R_3=R_4=100\ \Omega$. Their temperature coefficient is 0.005 per °C; all use the same material and temperature. At strain 0.01 and temperature 50 °C, output $V_o$ is ______ mV (two decimal places).
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Correct answer: 2.45 to 2.55
Explanation
The common temperature factor is 1+αΔT=1+0.005·50=1.25, so the unstrained resistance at 50°C is RT=125 Ω. With GFε=2·0.01=0.02, the opposing tensile/compressive arms are RT(1±0.02)=127.5 and 122.5 Ω. Both series branches total 250 Ω, so each receives 0.5 mA of the 1-mA excitation. The indicated output is 0.5 mA·(127.5−122.5) Ω=**2.50 mV**. Current excitation means the common temperature scaling does not cancel from output magnitude.