Derive Wheatstone Bridge's equation

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Homework Statement



how to derive this equation?
Equation: delta Vg = r/(1+r)^2 times (delta R1/R1 - delta R2/R2 + delta R3/R3 - delta R4/R4) times (1+r) Vin.


and

Equation for the Wheatstone bridge sensitivity: eta = 1 / (1 + r + ((ΔR1/R1 + ΔR4/R4 + r(ΔR2/R2 + ΔR3/R3)) / (1 + r))).


Homework Equations



Equation: Vg + ΔVg = [(R1 + ΔR1)(R3 + ΔR3) − (R2 + ΔR2)(R4 + ΔR4)] / [(R1 + ΔR1 + R2 + ΔR2)(R4 + ΔR4 + R3 + ΔR3)] × Vin


Equation V_g = (R1R3 - R2R4)/((R1+R2)(R4+R3)) V_in = 0, implying R1R3 = R2R4, or R1/R2 = R4/R3 = 1/r.


The Attempt at a Solution



I try derive it that to cut out high degree part such as delta_R1*delta_R2
because my teacher told that is very small and near to zero. but I can't made it to that given form. And i think Resistance that have change must be equal like as fraction R1*R3=R2*R4 so (R1+delta_R1)(R2+delta_R2)=(R3+delta_R3)(R4+delta_R4)

Now, I made the last expression to

delta_Vo = [deltaR1/R1-deltaR2/R2+deltaR3/R3-deltaR4/R4]/[2*(1+deltaR3/R3+deltaR4/R4)*(1+(deltaR1+R1)/(deltaR2+R2))]Vs


this is my first time for this forum and my english is not good. so if i do something wrong or someone can't understand me I'm very apologize.

I'd appreciate if someone can help me or tell me if i do wrong way.

Thanks a lot
 
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  • Equation: delta Vg = r/(1+r)^2 times (delta R1/R1 - delta R2/R2 + delta R3/R3 - delta R4/R4) times (1+n) times Vin
    WheatstoneBridge01EqF.gif
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We need a statement of the problem, namely what are you looking for? What do the symbols that you use stand for? I can understand R1, but what is ΔR1? What about Vg and ΔVg? Are you trying to find how the bridge becomes unbalanced when you change the four resistors by small amounts? You should be providing the details and definitions and we should not be guessing what they are.