A Wheatstone Bridge is to be used to measure changes in resistance, Delta R, ass

Question

A Wheatstone Bridge is to be used to measure changes in resistance, Delta R, associated with changes in strain. The Bridge is connected to a Multimeter, M, as shown that can either measure voltage or current. You may assume the meter is ideal. If Vin = 5 V, R0 = 100 Ohm, and Delta R changes from 1 Ohm to 2 Ohm find: The change in output voltage, Ohm Vout = Vout (Delta R=2Ohm)-Vout(Delta R=1 Ohm), when the multimeter is set to measure voltage. The change in output voltage, Delta Vout = Vout(Delta R=2 Ohm), when the multimeter is set to measure current.

Explanation / Answer

a) Iout=0 as resistance of multimeter will set to infinity

so current will only flow in bridge resistance:

current through R+dR=5/202 (for dR=2)

current through R+dR=5/201 (for dR=1)

therefore, change in output voltage= (-5/202*100+5/200*100)-(-5/201*100+5/200*100)= 0.0123v

b) in this setting of multimeter, the terminal points of the multimeter will work as common junction i.e short circuit

so, Vout(dR=2)=0

Vout(dR=1)=-5/201*100+5/200*100=0.0124v

hence dV= 0-0.0124= -0.0124v

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