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An off-shelf instrumentation amplifier manual has the following indication for Rb: enter image description here

And this force-transducer gives the following resistance parameter: enter image description here

I guess Rb is each single resistor value of the Wheatstone bridge.

But what could be meant by input resistance and output resistance regarding the force-transducer?

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But what could be meant by input resistance and output resistance regarding the force-transducer?

If the data sheet said input resistance was 350 ohm and output resistance was 350 ohm, I don't think you'd have much worry about that because, 4 x 350 ohms in a bridge gives you that equal input and output resistance. But, when the input resistance is quoted as higher than the output resistance, it makes you think. It's not entirely a guess (because I've come across it before in pressure bridges) but, I believe that extra resistance is due to temperature compensation like this: -

enter image description here

Picture of 4-arm Wheatstone bridge with temperature compensation.

So, from the point of view of the battery, it sees \$R_G+R_C\$. That's the input resistance. The output resistance remains unchanged at \$R_G\$.

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  • \$\begingroup\$ Interesting. I understand how input impedance is affected by Rs above. But couldnt derive the output(Thevenin) resistance in this case mostly because there is no ground at the output terminals. But I think it would be a different question. \$\endgroup\$
    – ty_1917
    Apr 2, 2020 at 13:07
  • \$\begingroup\$ Well, if Vcc was open circuit the output Z would be (\$R_G+R_G\$)||(\$R_G+R_G\$) = \$R_G\$. And, if you think about it, when sorting Vcc out it's just the same. \$\endgroup\$
    – Andy aka
    Apr 2, 2020 at 13:10
  • \$\begingroup\$ But to find Thevenin output impedance dont we short the independent voltage source Vcc in this case and look from the output terminals? \$\endgroup\$
    – ty_1917
    Apr 2, 2020 at 13:12
  • \$\begingroup\$ It's the same resistance whether Vcc is shorted or not when the bridge is balanced. \$\endgroup\$
    – Andy aka
    Apr 2, 2020 at 13:13

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