Question

A strain is used in one arm of the bridge to measure quantity 'x' as shown below. The unbalanced voltage is amplified using an ideal difference amplifier. The gain of the amplifier to give full scale output voltage for $\pm 2\%$ full scale change in quantity 'x' is?
There is a linear relationship between quantity 'x' and resistance of the gauge. The gauge factor is 2.0.

• A. 20
• B. 50
• C. 100
• D. 200

Answer 1

The correct option is D 200

Since 'x' and 'R' are linearly related $\pm 2\%$ change in 'x' will have same change in R.

$\therefore \text{Unbalanced voltage}{V}_0=\frac{\Delta R}{4R}{V}_s$

$\Delta R=\pm \text{2 \% of R = 2 \% of 300 =}6\Omega$

$\therefore V_0=\frac{6}{4\times 300}\times 10=50mV$

The full scale output voltage of differential amplifier can be $\pm 10V$(saturation voltage).

$\text{Hence the required gain =}\frac{10V}{50mV}$

$G=200$