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Observation periods

After most tests in GB 38031-2025, the standard requires a quiet observation period at the test environment temperature (22 °C ± 5 °C, RH 10 % – 90 %) before the pass/fail criterion is judged. The duration depends on the test category, and a few tests have category-specific rules. A handful of tests also require in-test monitoring of the smallest internal unit.

Observation period by test

Cell-level tests — 1 h

All cell-level tests use a 1-hour post-test observation period at the test environment temperature.

# Clause Test Observation
1 8.1.2 Over-discharge 1 h
2 8.1.3 Overcharge 1 h
3 8.1.4 External short circuit 1 h
4 8.1.5 Heating 1 h
5 8.1.6 Temperature cycling 1 h
6 8.1.7 Compression (extrusion) 1 h
7 8.1.8 Safety after fast-charge cycles 1 h (per the 8.1.4 step)

Source: GB 38031-2025 clauses 8.1.2.3, 8.1.3.4, 8.1.4.4, 8.1.5.x, 8.1.6.x, 8.1.7.x, 8.1.8.x (PDF pages 15–17).

Pack/system mechanical tests — 2 h

# Clause Test Observation
8 8.2.1 Vibration 2 h
9 8.2.2 Mechanical shock 2 h
10 8.2.3 Simulated collision 2 h
11 8.2.4 Compression (pack/system) 2 h
12 8.2.16 Bottom impact 2 h

Source: GB 38031-2025 clauses 8.2.1.6, 8.2.2.5, 8.2.3.x, 8.2.4.x, 8.2.16.x (PDF pages 18–22).

Pack/system environmental tests — 2 h

# Clause Test Observation
13 8.2.5 Damp heat cycling 2 h (insulation measured within 30 min)
14 8.2.6 Immersion 2 h
15 8.2.8 Temperature shock 2 h
16 8.2.9 Salt fog not specified separately ⚠
17 8.2.10 High altitude 2 h

The salt fog test (8.2.9) is the cycle itself; the standard does not state a distinct post-test observation period. Treat as per the cheatsheet's flagged note. See all tests at a glance for the verification flag.

Source: GB 38031-2025 clauses 8.2.5.x, 8.2.6.x, 8.2.8.x, 8.2.9.x, 8.2.10.x (PDF pages 19–21).

Pack/system electrical-protection tests — 1 h

All five electrical-protection tests use 1 h, not 2 h.

# Clause Test Observation
18 8.2.11 Over-temperature protection 1 h
19 8.2.12 Over-current protection 1 h
20 8.2.13 External short-circuit protection 1 h
21 8.2.14 Overcharge protection 1 h
22 8.2.15 Over-discharge protection 1 h

Source: GB 38031-2025 clauses 8.2.11.x – 8.2.15.x (PDF pages 21–22).

Thermal-stability tests — special rules

# Clause Test Observation
23 8.2.7.1 External fire 2 h or until external T < 45 °C, whichever occurs first ⚠ verify
24 8.2.7.2 / App C Thermal propagation Until all monitoring points ≤ 60 °C, minimum 2 h

For external fire the standard frames observation in terms of the test object cooling. For thermal propagation the criterion is set on the temperature monitoring points themselves.

Source: GB 38031-2025 clauses 8.2.7.1.x, 8.2.7.2 / Appendix C.5 (PDF pages 22–28).

In-test monitoring requirements

Some tests require monitoring during the test, not only afterward. The cheatsheet calls these out; the most prominent is vibration.

Vibration (8.2.1.5)

During the test, monitor the status of the smallest monitoring unit inside the test object, such as voltage, temperature, etc.

The "smallest monitoring unit" is the smallest unit the BMS exposes — typically a cell or cell-group sense channel. The test method does not prescribe a sample rate; clause 6.4 requires data recording intervals not exceeding 15 s unless otherwise specified.

Source: GB 38031-2025 clause 8.2.1.5 (PDF page 19); recording interval per 6.4 (PDF page 14).

Salt fog (8.2.9)

The salt fog test specifies low-voltage power-on monitoring during hours 4–5 of each spray cycle (per the cheatsheet entry at row 16). The 24-hour cycle is: 8 h spray at 35 °C followed by 16 h dwell, with low-voltage monitoring during hours 4–5 of the spray phase, repeated for 6 cycles.

Source: GB 38031-2025 clause 8.2.9 (PDF page 21); see all tests at a glance row 16.

Electrical-protection tests (8.2.11–8.2.15)

The electrical-protection tests have stop conditions that depend on in-test measurements: auto cutoff by the manufacturer's protection device, manufacturer signal, or a temperature-stability criterion (ΔT < 4 °C over 2 h). These are not observation periods in the post-test sense; they are termination conditions for the active phase. The 1-hour observation comes after termination.

Source: GB 38031-2025 clauses 8.2.11.x – 8.2.15.x (PDF pages 21–22).

Thermal propagation (8.2.7.2 / Appendix C.5)

Continuous monitoring of cell voltage, temperature at multiple points, smoke (in-cabin video for vehicle-level), and the warning signal timestamp is required throughout the test, not only after. The "until all monitoring points ≤ 60 °C, min 2 h" observation period is post-trigger.

Source: GB 38031-2025 Appendix C.5 (PDF pages 34–37).

Engineering note (non-normative): "Observation period" is a quiet wait at test temperature — not an active discharge or thermal cycle. The purpose is to give delayed events (latent vent, slow combustion onset) time to manifest. Plan instrumentation runtime to cover the full observation period plus a margin.

Cross-references