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1. Scope:
All EN/IEC standards with this requirement
If the applicable standard specifies other methods use these.
2. Subject:
EUT subject to humidity test or conditioning at high humidity.
3. Testing:
Introduction:
The purpose of the test is most often to find if there are hygroscopic materials used as insulation materials.
It is important the there is no condensation of liquid water as a result of the test or during the test (some standards seems to allow that and required it wiped off). Condensation should not occur if the chamber is working correctly (circulation of air inside), at the right Relative Humidity and precautions are taken not to expose a cold EUT to the humidity at higher temperatures than the EUT. If the EUT has parts that are colder than the dew-point inside the chamber when starting the test water will condense. If the humid EUT is exposed to cold temperature when taking the EUT out of the chamber for testing, water may condense on the EUT.
Execution of the test:
Before placing the EUT in the chamber, the chamber shall be brought to the correct temperature and humidity (Exception see below) and some time after the chamber has reached the correct temperature shall have passed to insure that the temperature distribution inside the chamber is uniform. Consult the calibration record or check if a special investigation has been made regarding a suitable duration for the temperature equalization. The EUT shall have a temperature in the interval t to t+4C, where t is the temperature of the chamber, before it is placed in the chamber. (If possible adjust the air-conditioner).
If the EUT is removed for a High voltage (Dielectric or insulation resistance) or leakage current test or similar the location outside the chamber shall be in the interval of t to t+4 C.
Exception:
If the outside chamber or room does not have the right temperature, the EUT shall be prepared for the test inside the chamber. In that case the chamber is brought to a temperature of t to t+4C with no humidity and the EUT is placed in the oven. The temperature is adjusted to t and the sample is conditioned at this temperature for 24 h. Humidity is thereafter applied.
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