Damp heat, cyclic (Test Db) - condensation during daily temperature changes.
A method for testing the suitability of components, equipment and other products for use, transport and storage under high humidity combined with cyclic temperature changes. The daily cycle causes water-vapor condensation on the specimen surface and reproduces enclosure “breathing” during temperature changes.
For small, low-mass specimens on which condensation is difficult to produce, the standard points to IEC 60068-2-38 as an alternative.
The test demonstrates that the product withstands repeated condensation and moisture ingress during day/night temperature changes, including moisture penetration into the enclosure during cooling. A reference without the upper temperature and number of cycles does not define severity; the combination is prescribed by the product standard.
The method checks behavior under cyclic humidity; long-term steady humidity is tested by Test Cab.
The specimen is stabilized in the chamber at 25 °C ±3 K, then humidity is raised to at least 95% RH and 24-hour cycles begin. Each cycle consists of a temperature rise to the upper value within 3 h ±30 min (humidity ≥95% RH, ≥90% during the last 15 min), holding at the upper temperature for 12 h ±30 min at 93% ±3% RH, then cooling to 25 °C ±3 K within 3–6 h and holding at 25 °C until the end of the 24 h period.
Variant 1 maintains ≥95% RH during cooling with a defined initial temperature-fall rate; Variant 2 permits ≥80% RH during cooling without a specified fall rate. The chamber maintains temperature within ±3 K and a difference between points ≤1 K, with no thermal radiation on the specimen; condensate (water resistivity ≥500 Ω·m) is continuously removed so that it does not drip onto the specimen.
Visual inspection and functional measurements are performed before testing; after testing, recovery is performed (standard or controlled: humidity reduced to 75% ±2% RH within 1 h, then laboratory temperature reached within the next hour) followed by final measurements, with humidity-sensitive parameters measured first, within 30 min.
Severity is defined by the combination of upper temperature and number of cycles, selected by the product specification.
Look for the upper temperature (40 or 55 °C), number of cycles and variant (1/2); without all three, “IEC 60068-2-30” describes only the procedure. Distinguish it from Test Cab (IEC 60068-2-78, steady humidity) - both often appear together in datasheets but test different degradation mechanisms.
