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33003405 07/2007
Internal
Convection
With internal heat convection, the heat is dissipated outside through the walls of the
housing. This is possible when the ambient temperature is lower than that inside the
housing.
The following table describes the variables used to calculate the internal convection:
* (1m
2
= 10.76ft
2
)
The maximum temperature increase of all electronic devices inside the housing is
calculated as follows:
The power dissipation P
v
can be calculated based on the values of the electrical
power of the controller, its inputs, and outputs.
Variable Description
P
v
[W] heat output (heat dissipation) of the electronic components
A [m
2
]*
effective surface area of the housing
k [W/m
2
K]*
the housing heat transfer coefficient
(e.g., Steel sheet: approximately 5.5 W/m
2
K)*
∆T()max
Pv
kA•
-------------=