Question

A single strain gauge of gauge factor 2 is used in a wheat-stone bridge where each resistance is $120\Omega$. If the bridge exciting voltage is 10 cos 1000t V and the gauge is subjected to sinusoidally varying strain of $500\mu m/m$ peak value with frequency of 10 Hz then the equation for output voltage as observed on a CRO (assuming infinite impedance for the CRO) is

• A. $2.5cos1000tsin20\pi tmV$
• B. $5cos1000tsin20\pi tmV$
• C. $10cos1000tsin20\pi tmV$
• D. 0 mV

Answer 1

The correct option is A $2.5cos1000tsin20\pi tmV$

Since the given bridge is the quarter bridge arrangement. Hence output voltage is given by

$V_0=\frac{V_{in}}{4}\times G\times ϵ$

$Here,V_{in}=10cos1000tV$

$ϵ=500sin(2a\times 10)t\mu m/m$

$=500sin20\pi t\mu m/m$

$G=2$

$V_D=\frac{\left(10cos1000t\right)\times 2\times \left[500sin20\pi t\right]\times {10}^{-6}}{4}$

$=2.5cos1000tsin20\pi tmV$