Problem of mould caused due to surrounding humidity
Humidity is one of the factors with heat that causes trouble in the controlling machine. How does humidity affect the controlling machine is considered below.
There are plurality of joint parts in controlling machine. Humidity is the great enemy of joint parts. Graph shows “relationship between corrosion and humidity”. It is understood that corrosion progresses rapidly when humidity exceeds 60%. Humidity of about 70% is the common level in Japan and therefore, countermeasures for humidity are extremely important in controlling machine. Moreover, corrosion progresses as temperature increases and countermeasures for heat must also be simultaneously considered along with countermeasures for humidity.
Ion migration is the phenomenon wherein metal ions are eluted from its surface when voltage is applied to metal when water molecules contained in air adhere to metal surface.
When ion migration progresses, there is danger of short circuit due to adjacent conductor(metal). Moreover, in most of the cases, circuit gets burnt by large current that flows at the instant when it makes contact with the conductor flowing, causing trouble of non-regeneration.
Water molecules contained in air adhere to the solid surface and form a thin film of water on the surface.
Solid (metal) surface to which voltage is applied, starts eluting as metal ions in this (abovementioned) state.
Metal eluted as ions are pulled by neighbouring conductor.
Metal film acts as a bridge between the conductors, causing short circuit thereby becoming a cause for failure.
*In most cases, the metal film is formed in dendrite shape and evaporates and disappears at the time of short circuit as it is very brittle. Therefore, failure by ion migration is a cumbersome condition which is not reproduced after occurrence.