Power Input

DO-160 Power Input (avionics/do160/power-input)

Use when the task is DO-160 Section 16 power input characteristics of airborne equipment: checking steady-state AC and DC voltage limits (normal and emergency), quantifying voltage-sag depth and voltage-surge height as percentages of nominal, verifying frequency-variation tolerance on AC buses, and confirming transient-recovery time after a sag or surge event. The module is data-driven: you supply the applicable limit values and category envelopes from the current revision, and the functions validate inputs, compute derived quantities, and give pass-fail margins.

Domain quick reference

• DO-160G Section 16 (power input) covers the electrical input characteristics of equipment connected to aircraft power: steady-state normal and emergency voltage limits, voltage sag and surge transients (assessed against the equipment category), frequency variation for AC buses, and recovery behavior after transients.
• Sag depth as percent of nominal: (V_nom - V_sag) / V_nom x 100. Worked: nominal 28.0 V, sag trough 21.0 V -> 25.0 percent.
• Surge height as percent of nominal: (V_surge - V_nom) / V_nom x 100. Worked: nominal 28.0 V, surge peak 32.2 V -> 15.0 percent.
• Frequency deviation: dev_hz = f_meas - f_nom, and percent of nominal. Worked: 412.0 Hz against 400.0 Hz -> 12.0 Hz, 3.0 percent. A 5.0 percent tolerance band is 380.0 to 420.0 Hz: 412.0 Hz passes, 422.0 Hz fails.
• Steady-state limits check: 27.5 V inside [22.0, 29.0] passes with margins (5.5 V low, 1.5 V high); 21.0 V fails the lower edge.
• Transient envelope check (duration and depth): 80.0 ms at 20.0 percent depth against a 100.0 ms / 25.0 percent envelope passes with margins (20.0 ms, 5.0 percent). Recovery: 60.0 ms against 100.0 ms allowable passes.
• Ripple as percent of nominal: amplitude = (V_peak - V_min) / 2. Worked: 29.0 V peak, 27.0 V minimum, 28.0 V nominal -> 1.0 V amplitude -> 3.5714 percent.
• Emergency range classification: with normal [22.0, 29.0] and emergency [18.0, 32.2], a measured 20.5 V is 'emergency-only'; 27.0 V is 'normal'; 15.0 V is 'out-of-range'.
• Typical aircraft buses: 115 VAC 400 Hz three-phase, 26 VAC, 28 VDC, and 270 VDC. The exact limit tables and category envelopes are revision-specific standard data; confirm them against the current revision (e.g. DO-160G) before freezing a test plan.

Workflow

1. Identify the power bus (AC or DC, nominal voltage, nominal frequency for AC) and the equipment category; pull the applicable normal and emergency limit values from the current revision as data inputs.
2. Verify the measured steady-state voltage against the normal band with voltage_within_limits, and quantify headroom with limits_margins.
3. When the equipment is rated for emergency operation, classify the measured voltage across both bands with emergency_range_check.
4. For captured transients, compute sag depth and surge height with sag_depth_percent and surge_height_percent.
5. Check the transient against its category envelope with transient_check (duration and depth margins), then confirm recovery with transient_recovery_ok.
6. For AC buses, compute frequency_deviation and check frequency_within_tolerance against the applicable tolerance.
7. Quantify DC ripple with ripple_percent.
8. Report the pass-fail verdicts and margins; flag every limit value that still needs confirmation against the current revision.

Pitfalls

• Confusing section 16 (power input) with section 20 RF susceptibility (do160/radio-frequency-susceptibility): both are "susceptibility" tests, but 16 is power-bus voltage and frequency behavior, while 20 is radiated and conducted RF immunity (RS103, CS114).
• Confusing this leaf with do160/environmental-qualification: that leaf scopes the whole DO-160 test matrix per equipment category; this leaf only does section 16 power-input calculations.
• Confusing this leaf with do178c/verification: coverage percentages there are structural software coverage (MC/DC, statement, decision), not voltage margins; route coverage questions to do178c/verification.
• Applying steady-state normal limits to transient events, or category envelopes to steady state; the two assessments use different bands.
• Mixing AC and DC conventions: frequency tolerance applies only to AC buses; a 28 VDC bus has no 400 Hz component to check.
• Computing sag depth against the trough value instead of nominal; the percent-of-nominal convention keeps sag and surge comparable.
• Forgetting that emergency-power limits are a separate, wider band (lower minimum) that only applies when the equipment is rated for emergency operation.
• Treating typical category values as fixed; DO-160 limit tables are revision-specific, so confirm every value against the current revision before freezing the test plan.

Behavior contract (gate 3)

The logic is exercised by the gate 3 contract test: scripts/test_power_input.py against scripts/power_input_logic.py (stdlib unittest, offline). Run: python3 scripts/test_power_input.py

Compliance

• Standards referenced, not reproduced: DO-160 text is proprietary (RTCA); summary-only per standards-map.yaml and brief 06.
• The module is data-driven: limit values and category envelopes are inputs, so no standard table is embedded in the code.
• compliance: STANDARDS-REF, gated: false.