The ramp rate on the spec sheet was measured in an empty chamber at 23°C ambient. This calculator shows what your chamber achieves with your DUT loaded — and whether it can run the test profile you've written.
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Loaded Ramp Rate Calculator
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Selects typical cooling capacity and baseline load for this class of chamber.
From the manufacturer's capacity curve at your T-low — not the headline spec.
W
Power consumed maintaining workspace temperature with no DUT. Typically 25–35% of rated capacity.
W
kg
From your test profile or standard — IEC 60068-2-14, JEDEC JESD22-A104, ISO 16750-4.
°C/min
Used to estimate dwell time requirement.
Low
°C
High
°C
Thermal mass
1,800
J/K
DUT cooling power
150
W
Ramp profile — specified vs. achievable
Specified Achievable
Power demand vs. capacity
BaselineDUT loadCapacity
✓
Within capacity
Chamber can achieve the required ramp rate with this load.
Achievable ramp rate under load
24.0
°C/min
Minimum dwell time for thermal equilibrium
—
min @ 95%
—
min @ 99%
How this calculation works
Thermal mass = mass (kg) × specific heat capacity (J/kg·K). Required cooling power for the DUT: P = m × Cp × (dT/dt), where dT/dt is your ramp rate in K/s. Add the baseline load to get total power demand. Achievable ramp rate under load: (capacity − baseline) / thermal mass × 60.
Dwell time is estimated from the thermal time constant τ = m × Cp / (h × A), where h ≈ 25 W/m²·K (forced air) and A is estimated from mass and density. Minimum dwell for 95% equilibrium = 3τ; for 99% = 5τ. Verify with a thermocouple on the DUT during a trial run.
This is a first-order estimate. The manufacturer's cooling capacity curves give more accurate input than the headline figure. Capacity at -40°C is typically 40–60% of capacity at 0°C for single-stage chambers.