IEC 60721-3-9:20 24对在IEC 60721-3-3和IEC 60721-3-4中分类的气候条件下使用的产品内部组件（基本零件、组件、内置单元）可能受到的小气候条件组进行了分类。 这第二版取消并取代了1993年出版的第一版、修正案1:19 94和勘误1:19 95。本版构成技术修订版。 与上一版相比，此版本包括以下重大技术变更: a)第2条已更新； b)重新编辑和简化了第4条； c)对附件A进行了修订和更新； d)增加了新的附件B，给出了湿空气组成图的由来，这是绘制小气候气候图的基础。

IEC 60721-3-9:2024 classifies groups of microclimatic conditions, to which components (basic parts, assemblies, built-in units) can be subjected inside products, which are used under the climatic conditions as classified in IEC 60721-3-3 and IEC 60721-3-4.
This second edition cancels and replaces the first edition published in 1993, Amendment 1:1994 and Corrigendum 1:1995. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
a) Clause 2 has been updated;
b) Clause 4 has been re-edited and simplified;
c) Annex A has been revised and updated;
d) a new Annex B has been added and gives the origin of the constitutional diagram for humid air, which is the basis of drawing the climatogram for a microclimate.