Image Processing Reference
In-Depth Information
Infallible current
Limiting resistor
Wireless
Capacitor bank
for short radio
transmission
vibration
sensor
FIGURE .
Battery design.
Depending on the specified tolerance of the device components, a high or low temperature can
force the device to have a thermally insulating housing, or some kind of cooling mechanism to protect
its internal components. Thermal insulation housing consists of materials that do not transfer heat
quickly, in order to separate and insulate the sensitive internal components from the external tem-
perature. It is also possible to have a thermally insulating barrier, a non-heat conducting material
positioned between the hot/cold part and the critical part of the device.
There are different kinds of cooling mechanisms available: active, such as fans, and passive, such as
heat sinks and heat pipes. A problem with active cooling components is that they also wear out and
could pose problems if they fail, e.g., overheating. This would require maintenance of the cooling
mechanism on the device, possibly outside the normal maintenance schedule, which is too costly.
Thus, active cooling is not a desirable solution.
27.7.4 Form Factor
The form and shape of an embedded device is very important. It depends on various requirements,
such as
•
The environment where the device will be located, which usually is very close to the
process it will monitor
•
Possible reuse of legacy housing
•
Mounting requirements
•
Design guidelines of the device manufacturer
The housing material of the device is also a very important part of the form factor. As mentioned
in the previous subsection, there might be a requirement for the material to be thermally insulat-
ing or cooling, or just that it should be rugged, which also affects the physical dimensions of the
device, e.g., weight difference between a metal and a plastic housing. Casting or filling also affects
the weight of the device, and can also make component replacement or upgrading impossible, e.g.,
battery replacement.
The power source, e.g., a battery or capacitor, will affect both the weight and physical shape of the
device, and thus has a major influence on the design. Batteries (and capacitors) have a correlation
between stored power and physical dimensions, i.e., larger batteries can store more energy. If the
form factor forces a certain maximum physical size for the power source, the device's life length will
