Suppose the strain gages in the bridge in Figure. 1. have the value 120 Ω ± 1%. The power...

Suppose the strain gages in the bridge in Figure. 1. have the value 120 Ω ± 1%. The power supplies to the op amp are ±15V, and the reference voltage, υrcf, is taken from the positive power supply.

a) Calculate the value of R¡ so that when the strain gage that is lengthening reaches its maximum length, the output voltage is 5 V.

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b) Suppose that we can accurately measure 50 mV changes in the output voltage. What change in strain gage resistance can be detected in milliohms?

Figure. 1