Training Signal Conditioning Practice Test — Signal Conditioning
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Practice Test — Signal Conditioning

30 min Signal Conditioning

Practice Test — Signal Conditioning

This practice test covers bridges, instrumentation amplifiers, filters, noise, and ADCs — the full signal chain from a sensor to software. Work through the 15 problems consecutively, attempting each without notes, and then review the key. These problems mirror the combined conceptual and numerical questions typical of a sensors-and-instrumentation qualifying examination.

Practice Problems

1. Quarter bridge: $V_s = 5\,\text{V}$, $\Delta R/R = 5\times10^{-3}$. Find $V_o$.
2. Full bridge with the same inputs: $V_o$?
3. Quarter bridge exact formula for $\Delta R/R = 0.02$: $V_o/V_s$?
4. AD620-style in-amp, $R_1 = 24.7\,\text{k}\Omega$. $G$ with $R_G = 500\,\Omega$?
5. Same in-amp, what $R_G$ gives $G = 1000$?
6. CMRR = 90 dB. Rejection ratio?
7. $V_{\text{OS}} = 25\,\mu\text{V}$, $G = 200$. Output offset?
8. $R = 10\,\text{k}\Omega$ at 300 K, noise in 1 kHz bandwidth?
9. $f_c$ for RC with $R = 1\,\text{k}\Omega$, $C = 1\,\mu\text{F}$?
10. 12-bit ADC, 3.3 V range, LSB?
11. ENOB for 14-bit ADC with 400 µV RMS noise at 5 V range?
12. Why does increasing $V_s$ on a bridge eventually fail to improve SNR?
13. In a full bridge, what happens if all four arms see the same strain?
14. Why is a shielded twisted-pair preferred for bridge leads?
15. Nyquist rate for a 4 kHz bandlimited signal?
Show Answer Key

1. $V_o = (5/4)\cdot 5\times10^{-3} = 6.25\,\text{mV}$.

2. $V_o = 5\cdot 5\times10^{-3} = 25\,\text{mV}$.

3. $0.02/(4 + 0.04) = 0.00495$.

4. $G = 1 + 2\cdot 24700/500 = 1 + 98.8 = 99.8$.

5. $1000 = 1 + 49400/R_G \Rightarrow R_G = 49400/999 \approx 49.4\,\Omega$.

6. $10^{90/20} = 10^{4.5} \approx 31{,}600$.

7. $200\cdot 25\,\mu\text{V} = 5\,\text{mV}$.

8. $V_n = \sqrt{4\cdot 1.38\times10^{-23}\cdot 300\cdot 10^4\cdot 10^3} = 4.07\times10^{-7}\,\text{V} = 0.41\,\mu\text{V RMS}$.

9. $f_c = 1/(2\pi\cdot 10^3\cdot 10^{-6}) = 159\,\text{Hz}$.

10. $3.3/2^{12} = 0.806\,\text{mV} = 806\,\mu\text{V}$.

11. Full-scale RMS = $5/2.83 = 1.77\,\text{V}$. SNR = $20\log(1.77/400\mu) = 20\log(4419) = 72.9\,\text{dB}$. ENOB = $(72.9-1.76)/6.02 = 11.8\,\text{bits}$.

12. Self-heating in the bridge resistors introduces additional drift and noise.

13. Output is zero — uniform strain is rejected as common-mode geometric change.

14. Twisted pair cancels inductive pickup; shield cancels capacitive pickup. Together they deliver a clean differential signal to the in-amp.

15. $f_s \ge 2\cdot 4\,\text{kHz} = 8\,\text{kHz}$.

Filters, Noise, and the ADC Back to Module