EE 5340 Name:___________________

April 9, 1997 Signature^* :___________________

Instructor: C. Davila

1. Assume the unbonded strain gauge wire has a gauge factor of 2.1 and each resistance has an equilibrium value of 1 W. Determine the length of wire needed for each resistance if the strain gauge is to have a sensitivity of 1 mv/mm. Assume the resistive bridge input voltage is 1 V and each resistance consists of a 5-turn coil of wire. (10 pts)
   
2. Consider the following differential temperature sensor:
   

   R_T1 and R_T2 are thermistors which measure temperatures T₁ and T₂, respectively. Assume that T₂ = 298 ^oK, T₀ = 273 ^oK, b = 3000 ^oK, and R₀ = 100 W. Plot V_o as a function of T₁ for T₁ = 270, 280, 290, 300, 310, 320 ^oK. Then determine the independent nonlinearity expressed as a percentage of full-scale (320 ^oK), based on the 6 values of V_o. Assume the difference amplifier has high input resistance. (10 pts)
   

3. Describe what reactions take place and determine the voltage V between the silver chloride electrode and the iron electrode. Use the half-cell potentials in the lecture notes. What would you expect to happen if the FeCl₂ solution is agitated? (10 pts)
   
   

4. Three evoked potential waveforms, x₁, x₂, and x₃, are to be averaged using two types of averages. The first is the conventional average discussed in lecture, the second is a weighted average. The signal components in x₁, x₂, and x₃ are denoted by s₁, s₂, and s₃, respectively and are related by s₂ = 3s₁ and s₃ = 2s₁. The signal power in s₁ equals 1. The weighted average is found by multiplying each waveform by the square root of its signal power prior to averaging the three waveforms. Assume the noise in each waveform has zero mean, a variance of 1, and is uncorrelated across the 3 trials. Find the signal to noise ratio of the conventional average and the weighted average. (10 pts)