cee291_10_sp_hw7_sol

cee291_10_sp_hw7_sol - E0 100 Ei 60 -12 dB +32 filter...

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E i amplifier filter -12 dB +32 dB 100 Ω 60 Ω E 0 Spring 2010 CEE 291 - Homework 7 Problem 1 A strain gauge – force sensor, which changes its output resistance as it is loaded, forms one leg (R 1 ) of the Wheatstone bridge, page 18 of notes. The sensitivity coefficient of the sensor to loads is 0.5 Ω/N; at no load, the sensor resistance is 500 Ω. The fixed resistance of R 3 and R 4 is 500 Ω. a) For measurements as a balanced (null mode) bridge, how would R 2 vary with load, L, applied to the sensor? = = + . * R1 R2 R1 500Ω 0 5ΩN L b) For measurements as an out-of balance (deflection mode) bridge with R 2 = 500Ω = fixed resistance, determine the bridge output voltage for an input voltage of 10 V and load of 930 N applied to the force sensor. Assume the voltmeter has an input impedance of ∞ so that I g = 0 (no current flow through the meter). = , = , = L 930 N Ei 10V R2 500Ω = + . * = R1 500Ω 0 5ΩN 903N 965Ω = + - + = . Em EiR1R1 R2 R3R3 R4 1 587V c) For the conditions in part (b), what is the current flow through the sensor? = = I1 I2 since Ig 0
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cee291_10_sp_hw7_sol - E0 100 Ei 60 -12 dB +32 filter...

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