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So the analysis works in two directions:
1) The study of the
emission problems, the disturbances generated by the
device and the possible countermeasure to prevent the propagation of that
energy; we talk about “conduction” issues when guiding structures such as
wires and cables are involved, “radiated emissions” issues when it is studied
the propagation of electromagnetic energy through the open space. In our
case the origin of the disturbances can be found inside the controller with the
switching of the mosfets which are working at high frequency and generate
RF energy,
but wires and cables have the key role to propagate the
disturbs because they works as antennas , so a good layout of the cables
and their shielding can solve the majority of the emission problems.
2) The study of the
immunity can be divided in two main branches: protection
from electromagnetic fields and from electrostatic discharge.
The
electromagnetic immunity concern the susceptibility of the controller
with regard to electromagnetic fields and their influence on the correct work
made by the electronic device.
There are well defined tests which the machine has to be exposed to.
These tests are carried out at determined levels of electromagnetic fields, to
simulate external undesired disturbances and verify the electronic devices
response.
3) The second type of immunity,
ESD , concerns the prevention of the effects of
electric current due to excessive electric charge stored in an object. In fact,
when a charge is created on a material and it remains there, it becomes an
“electrostatic charge”; ESD happens when there is a rapid transfer from a
charged object to another. This rapid transfer has, in turn, two important
effects:
A) this rapid charge transfer can determine, by induction, disturbs on the
signal wiring and thus create malfunctions; this effect is particularly
critical in modern machines, with serial communications (canbus)
which are spread everywhere on the truck and which carry critical
information.
B) in the worst case and when the amount of charge is very high, the
discharge process can determine failures in the electronic devices; the
type of failure can vary from an intermittently malfunction to a completely
failure of the electronic device.
IMPORTANT NOTE : it is always much easier and cheaper to avoid ESD from
being generated, than to increase the level of immunity of the electronic devices.
There are different solutions for EMC issues, depending on level of emissions/
immunity required, the type of controller, materials and position of the wires and
electronic components.
1)
EMISSIONS . Three ways can be followed to reduce the emissions:
A) SOURCE OF EMISSIONS: finding the main source of disturb and work
on it.
B) SHIELDING: enclosing contactor and controller in a shielded box; using
shielded cables;
C) LAYOUT: a good layout of the cables can minimize the antenna effect;
cables running nearby the truck frame or in iron channels connected to
truck frames is generally a suggested not expensive solution to reduce