Sensors & Signal Conditioning — Cheat Sheet
Bridges, gain, filters, ADC resolution, noise, 4–20 mA and thermocouples.
Bridges & strain
| Gauge factor | GF = (ΔR/R) / ε |
| Quarter bridge | V_o/V_ex = GF·ε / 4 |
| Half bridge | V_o/V_ex = GF·ε / 2 |
| Full bridge | V_o/V_ex = GF·ε |
| Load cell output | V_o = V_ex · (mV/V) · load/capacity |
Amplification & filters
| Non-inverting gain | G = 1 + R_f/R_g |
| Instrumentation amp | G = 1 + 2R_1/R_g |
| RC low-pass | f_c = 1 / (2πRC) |
| Time constant | τ = RC; 5τ ≈ settled |
| Anti-alias | f_c well below f_s/2 (Nyquist) |
ADC & resolution
| LSB | V_ref / 2ⁿ |
| Ideal SNR | SNR = 6.02n + 1.76 dB |
| ENOB | (SNR − 1.76) / 6.02 |
| Counts | 2ⁿ (12-bit = 4096) |
| Oversampling | +1 bit per 4× samples |
Current loop & temperature
| 4–20 mA span | I = 4 + 16·(x − min)/(max − min) |
| Sense resistor | 250 Ω → 1–5 V |
| Max loop R | (V_supply − V_tx,min) / 0.02 |
| NTC (Beta) | 1/T = 1/T₀ + (1/B)·ln(R/R₀), T in K |
| RTD (Pt100) | R = R₀(1 + α·T), α ≈ 0.00385 |
| Thermocouple | needs cold-junction compensation |
Formula reference — verify against the governing standard. Not a substitute for engineering judgment.