Analog Front-End and Calibration Interface

Between raw sensor and digital sample sits the analog front end; its interface defines conditioning, ADC quantization, and the calibration chain.

Turning volts into trusted numbers

Every physical interface ultimately produces a voltage that must be conditioned, digitized, and calibrated before any layer trusts it. The analog front end (AFE) sets gain, filtering, and anti-alias limits; the ADC sets resolution and dynamic range; the calibration chain makes the number traceable. This is the interface that decides a reading's noise floor and its truth.

The chain

# raw voltage -> engineering unit (per channel)
v_cond = afe_gain[ch]*(v_raw - offset[ch])       # condition
v_filt = antialias_filter(v_cond, f_cut[ch])     # before sampling
code   = adc_sample(v_filt, bits[ch])            # quantize
value  = calib_poly[ch](code) * unit[ch]         # traceable EU
value  = drift_correct(value, cal_epoch[ch])     # apply latest cal

Two design choices dominate: the anti-alias filter must sit below the Nyquist limit for the channel's sample rate, and the ADC dynamic range must cover both quiescent noise and the largest transient without clipping. A channel that clips during a disruption is worse than useless because it corrupts the reconstruction.

Calibration and drift

• Per-channel calibration polynomial with an epoch and uncertainty.
• Drift tracking: readings tagged with the age of their last calibration.
• Health: dead-sensor and out-of-range detection before ingestion.
• Feeds the calibration provenance record.

Owner: L2 for the AFE/ADC and calibration store. Every downstream layer consumes engineering-unit values that carry their calibration provenance, so the twin and copilots never reason on an uncalibrated or stale number. Design-and-simulation specification, applied identically across both machines' 60+ port channels.