Question

A bridge circuit has two fixed resistor and two strain gauges, all of which have a value of $120\Omega$. The gauge factor is 2.04 and strain applied to twin strain gauges, one in tension & the other in compression is $165\times {10}^{-6}$. The battery current is 50mA. If the galvanometer connected to output terminals reads $100\mu V$ per scale division and if 1/10th of a division can be read with confidence then sensitivity in $\left(\mu V/\mu strain\right)$ is

• A. 4.53
• B. 3.53
• C. 1.53
• D. 5.00

Answer 1

The correct option is C 1.53


$\text{Supply voltage}\left(e_i\right)=120\times 50\left(mA\right)$
$=6V$

$\frac{\Delta R}{R}=G_f\epsilon =2.04\times 165\times {10}^{-6}$

$=3.366\times {10}^{-4}$

$e_o=\frac{e_i}{2}\frac{\Delta R/R}{(4+(2\Delta R/R\left)\right)}$

$=\frac{6}{2}\times \frac{3.366\times {10}^{-4}}{(4+(2\times 3.366\times {10}^{-4}\left)\right)}$

$e_0=0.252\left(mV\right)$

$\text{sensitivity}=\frac{e_0}{\text{strain}}$

$=\frac{0.252\left(mV\right)}{165\times {10}^{-6}\left(strain\right)}$

$=\frac{0.252}{165}\left(\frac{mV}{\mu strain}\right)$

$=1.527\left(\frac{\mu V}{\mu strain}\right)$