Iveco Daily. Manual - part 363
20
ELECTRIC/ELECTRONIC SYSTEM
D
AILY
Base - May 2004
The electric system is traditionally a single-pole system. The body, the frame, the metal container of electromechanical
components act as equipotential return conductor to the generator, as any point of their metal structure or any negative terminal
not isolated is at the same reference potential or EARTH. This is why the earth has been chosen as reference to the whole system,
conventionally giving it the value of zero.
Due to obvious reasons of construction, in the negative network of the system there are various earth points located on the
vehicle in relation to the location of the components on the frame, engine and body.
On the other hand, ideally, all the equipment should be connected to only one earth point in order to provide them, particularly
for electronic devices, a clearly defined earth reference.
For the above-mentioned reasons it is necessary to distinguish the supply earth or system earth, characterised by strong direct
current intensity (> 1 A for electromechanical components), from the analogue earth, characterised by wave shapes at
determinate frequencies and very low current intensity (mA, µA) of electronic systems.
The definition of signal earth or analogue earth depends on the sensitivity of the electronic systems to EMC (electromagnetic
compatibility), as parasite signals emitted by the systems on board or outside the vehicle, induce failures and/or deterioration of
the systems themselves. The best solution for a signal earth is connection with the battery negative terminal.
In order to minimise both continuous and transient disturbance or interference generated by parasite radiation, it is of the utmost
importance to always bear in mind that the satisfactory efficiency of the reference plane or system earth depends on the excellent
conductivity characteristics (contact resistance tending towards zero) in each of its connection points.
Briefly, we can say that the earth understood as equipotential electrical conductor, i.e. as potential reference for all the
electric/electronic components on board, is subdivided into system earth and analogue earth.
IDEAL EQUIPOTENTIAL EARTH NETWORK
Ba. Battery - R. Loads - Rz. Frame impedance - M
1
, M
2,
M
3.
Earth
Figure 18
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